To see the other types of publications on this topic, follow the link: Monomère activé.
Journal articles on the topic 'Monomère activé'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Monomère activé.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Mizutani, Masato, Kotaro Satoh, and Masami Kamigaito. "Construction of Vinyl Polymer and Polyester or Polyamide Units in a Single Polymer Chain via Metal-catalyzed Simultaneous Chain- and Step-growth Radical Polymerization of Various Monomers." Australian Journal of Chemistry 67, no. 4 (2014): 544. http://dx.doi.org/10.1071/ch13476.
Full textAbstract:
Metal-catalyzed simultaneous chain- and step-growth radical polymerization was examined to combine common conjugated vinyl monomers, such as various acrylates and styrene, as chain-growth monomers and various ester- or amide-linked monomers bearing both an unconjugated C=C bond and an active C–Cl bond as step-growth monomers. The CuCl/1,1,4,7,10,10-hexamethyltriethylenetetramine-catalyzed copolymerization of alkyl acrylates and various step-growth monomers at a 1 : 1-monomer feed ratio resulted in almost linear random copolymers that consisted of vinyl polymer and polyester units. Additional functional groups, such as oxyethylene and disulfide units, can be introduced into the main chain using a step-growth monomer that possesses the functional units between the unconjugated C=C bond and the active C–Cl bond. Copolymerization at a higher feed ratio of chain-growth monomers, such as alkyl acrylates and styrene, can provide multiblock vinyl polymers connected to the functionalized step-growth monomer units.
2
Kohut, Ananiy, Roman Fleychuk, Orest Hevus, and Stanislav Voronov. "Macroinitiators on the basis of new peroxide surface active monomers." Chemistry & Chemical Technology 1, no. 2 (June 15, 2007): 83–86. http://dx.doi.org/10.23939/chcht01.02.083.
Full textAbstract:
The surface active properties of new peroxide maleic monomers were investigated. The regularities of their copolymerization with styrene were studied. Peroxide polymers containing ditertiary alkyl peroxide groups in side substituents of backbone as the prospective high-temperature free radical macroinitiators were synthesized.
3
Si, Fuchun, and Wenbin Wang. "Effects of formula composed of active monomers of removing heat and phlegm prescription on malignant phenotypes and growth signaling in esophageal carcinoma cells." Journal of Clinical Oncology 39, no. 15_suppl (May 20, 2021): e16051-e16051. http://dx.doi.org/10.1200/jco.2021.39.15_suppl.e16051.
Full textAbstract:
e16051 Background: Esophageal carcinoma (EC) ranks seventh in the incidence of malignant tumors and the sixth mortality worldwide. Removing heat and phlegm prescription(RHPP, composed of Rhizoma Dioscoreae Nipponicae, Rhizoma Paridis, Saponin, Rhizoma Bolbostemmae) was an effective formula screened from 531 Chinese herbs for treating EC in our previous study. The purpose of this study is to further track, isolate, purify and identify the active monomers of RHPP, study the effect of each active monomer on Eca109, EC9706, EC-1, TE-1 four EC cells and the signaling mechanism, then optimize and compose new active monomers formula and study its mechanism on EC cells. Methods: The active monomer of RHPP was extracted, separated and identified by ethanol extractioncolumn, chromatography, recrystallization, HPLC, spectroscopic method,etc. The effects of four kinds of active monomers and their composed formula on the proliferation, migration, clone formation, cell cycle and signal pathway proteins expression of Eca109 cell, EC9706 cell and TE-1 cell were investigated by MTT assay, RTCA assay, soft agar assay, flow cytometry and western blot analysis. Results: Four active monomers were identified from Rhizoma Dioscoreae Nipponicae (CSL), Saponin (ZJ), Rhizoma Bolbostemmae (TBM), Rhizoma Paridis (CL) respectively with molecular weights of 868, 1003, 1365, 854.5, and corresponding molecular formulas of C45H72O16, C50H82O20, C64H100O31 and C44H70O16(China patient No. ZL202010136431.6). Four active monomers significantly affected the cell morphology, proliferation, migration, cloning ability, cell cycle of four EC cells. The IC50 values of the active monomer of CSL, ZJ, TBM and CL for Eca109 were 1.29±0.12, 2.42±0.09, 1.93±0.09, 3.04±0.28μg/ml respectively; for EC9706 were 1.41±0.02, 5.94±0.45, 1.97±0.09, 0.63±0.04μg/ml respectively; for TE-1 were 3.72±0.28, 35.58±0.58, 7.90±0.41, 1.85±0.09μg/ml respectively; for EC-1 were 1.11±0.14, 3.56±0.28, 1.23±0.02, 0.61±0.02μg/ml respectively. Four active monomers could downregulate EGFR, PLC-γ1, and PKCα protein expression. Using the baseline proportional increase and decrease design method to compose new removing heat prescription(RH), removing phlegm prescription(RP) and removing heat and phlegm prescription (RHPP), the ratio of each drug monomer in RH, RP and RHPP were mCSL: mCL = 6: 4, mZJ: mTBM = 3: 7, mCSL: mCL: mZJ: mTBM = 48: 32: 6: 14. RH, RP and RHPP all could inhibit the proliferation, migration, cloning ability, cell cycle of four EC cells. Conclusions: The four active monomers and new composed RHPP all can inhibit the proliferation of EC9706, Eca109, TE-1, EC-1 four EC cells, which have close relationship with EGFR, PLC-γ1, and PKCαproteins expression. This study provides new formula and basis for the development of anti-esophageal carcinoma drugs in traditional Chinese medicine.
4
Borzenkov, Mykola, and Orest Hevus. "Synhtesis of Novel Surface Active Methacrylate Monomers Based on ε-Caprolactone." Chemistry & Chemical Technology 8, no. 2 (June 25, 2014): 141–46. http://dx.doi.org/10.23939/chcht08.02.141.
Full text
5
Mortensen, E. R., J. G. Drachman, and G. Guidotti. "The αβ monomer of the insulin receptor has hormone-responsive tyrosine kinase activity." Biochemical Journal 273, no. 1 (January 1, 1991): 49–56. http://dx.doi.org/10.1042/bj2730049.
Full textAbstract:
Insulin receptors from turkey erythrocyte membranes exist as monomers and dimers when membranes are solubilized with detergent. We examined the ability of monomers and dimers to act as protein kinases to effect both autophosphorylation of the receptor and phosphorylation of an exogenous substrate. After separation by sucrose-density-gradient centrifugation, only receptor dimers show significant basal and insulin-stimulated kinase activity, whereas material at the position of receptor monomers is not active. Partial reduction of the membrane-bound receptors with dithiothreitol, however, produces a receptor monomer containing an alpha and a beta chain which has protein kinase activity similar to that of the original dimers. With rat adipocyte plasma membranes, which in the absence of reducing agents only contain receptor dimers, reduction with dithiothreitol also produces monomers with receptor kinase activity. Receptor monomer hormone-dependent kinase activity is insensitive to receptor concentration and shows stimulation after immobilization on an affinity support.
6
Borzenkov, Mykola, Larysa Dolynska, Viktoriia Kochubei, Zoriana Nadashkevich, and Orest Hevus. "Obtaining of Functional Surface Active Monomers Based on tert-Butylperoxy-6-hydroxyhexanoate." Chemistry & Chemical Technology 5, no. 4 (December 15, 2011): 363–66. http://dx.doi.org/10.23939/chcht05.04.363.
Full text
7
Estrin, Yakov. "Bimodality of molecular mass distribution of polydienes obtained under the action of dilithium initiators in hydrocarbon media: the reasons, mathematical simulations, and their experimental testing." Open Chemistry 2, no. 1 (March 1, 2004): 52–81. http://dx.doi.org/10.2478/bf02476184.
Full textAbstract:
AbstractBimodal molecular mass distribution (MWD) of polymers, obtained upon polymerization of hydrocarbon monomers in the nonpolar media under the action of dilithium initiators, is the consequence of separation of the reaction mixture into two phases. Bifunctional /living/ oligomers produce the insoluble sediment due to tetrameric association of the lithium active sites (the swollen gel-fraction). Part of the active site remains in the solution (the solfraction). Difference in the concentrations of the active sites into the phases leads to difference between the propagation rates of the /living/ chains and, as a result, to Bimodal MWD. The mathematical model of polymerization in the two-phase system is proposed. Satisfactory agreement between the calculations and the experiments is shown for butadiene polymerization in heptane under the action of 1,4-dilithiumpentane. Regulation of MWD up to the complete elimination of bimodality is possible via the programmed dosage of monomer and solvent into the reactor.
8
Blaby, I. K., and D. K. Summers. "The role of FIS in the Rcd checkpoint and stable maintenance of plasmid ColE1." Microbiology 155, no. 8 (August 1, 2009): 2676–82. http://dx.doi.org/10.1099/mic.0.029777-0.
Full textAbstract:
Escherichia coli plasmid ColE1 lacks active partitioning, and copies are distributed randomly to daughter cells at division. The plasmid is maintained stably in the bacterial population as long as its copy number remains high. The accumulation of plasmid dimers and higher multimers depresses copy number, and is an important cause of multicopy plasmid instability. ColE1 dimers are restored to the monomeric state by site-specific recombination, which requires the host-encoded proteins XerCD, ArgR and PepA acting at the plasmid cer site. In addition, a 70 nt RNA expressed from the cer site of plasmid dimers delays the division of dimer-containing cells. Here, we report that the global regulator FIS binds to cer in a sequence-specific manner, close to the Rcd promoter (P cer ). FIS is not required for plasmid dimer resolution, but is essential for repression of P cer in plasmid monomers. Repression also requires the XerCD recombinase, but not ArgR or PepA. We propose a model for monomer–dimer control of P cer in which the promoter is repressed in plasmid monomers by the concerted action of FIS and XerCD. Rcd transcription is triggered in plasmid dimers by the lifting of XerCD-mediated repression in the synaptic complex.
9
Rodionova, Raisa V. "SYNTHESIS AND INVESTIGATION OF PROPERTIES OF NANODISPERSED SYSTEMS BASED ON VINYL ACETATE." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 63, no. 9 (August 5, 2020): 56–62. http://dx.doi.org/10.6060/ivkkt.20206309.6079.
Full textAbstract:
A method of producing nanodispersed systems, stabilized by the solvation mechanism, which consists of carrying out the emulsion polymerization with surface-active monomers – alkyletoksimaleinata, is developed. The influence of temperature, the ratio of monomers, the hydrocarbon radical length and number of ethoxy functional groups on the rate of the process of obtaining nanodispersions is analyzed. The study of the properties of synthesized nanodispersed systems and aggregate storage stability showed that all indicators are within certain State Standards. The spectrophotometric analysis of nanodispersions showed that emulsion polymerization occurred in all cases. Kinetics of decomposition of the initiator in aqueous solutions in the presence of surface-active monomer showed that alkyletoksimaleinata activates the stage of initiation of obtaining nanodispersed systems. Alkyletoksimaleinata proved to be more effective than widely used in emulsion polymerization the emulsifier OP-10. It is established that nanodispersed systems are stable during storage. The use of nanodispersed systems, modified by surface-active monomers, makes it possible to exclude the stage of plasticization by low-molecular compounds that degrade the electrical properties of the product. This leads to a reduction in the material and energy costs, to an increase in the life of the product, since in this case there is no exudation of the plasticizer, which worsens the quality of the product and causes environmental pollution. It is established that the main role in the stability of nanodispersed systems, modified by surface-active monomers, plays the hydration of particles. The technology of production of modified nanodispersed systems based on vinyl acetate and surface-active monomer is developed. The technological scheme of production of modified nanodispersed systems is arranged, the binding of the main apparatus is made. Rational use of raw materials will allow to obtain a higher yield of the product. The nanodispersed systems, modified by surface-active monomers, can be used in all areas where systems with conventional emulsifiers are used.
10
Whang, I., J. Lee, and M. Jayaram. "Active-site assembly and mode of DNA cleavage by Flp recombinase during full-site recombination." Molecular and Cellular Biology 14, no. 11 (November 1994): 7492–98. http://dx.doi.org/10.1128/mcb.14.11.7492.
Full textAbstract:
A combination of half-site substrates and step arrest mutants of Flp, a site-specific recombinase of the integrase family, had earlier revealed the following features of the half-site recombination reaction. (i) The Flp active site is assembled by sharing of catalytic residues from at least two monomers of the protein. (ii) A Flp monomer does not cleave the half site to which it is bound (DNA cleavage in cis); rather, it cleaves a half site bound by a second Flp monomer (DNA cleavage in trans). For the lambda integrase (Int protein), the prototype member of the Int family, catalytic complementation between two active-site mutants has been observed in reactions with a suicide attL substrate. By analogy with Flp, this observation is strongly suggestive of a shared active site and of trans DNA cleavage. However, reactions with linear suicide attB substrates and synthetic Holliday junctions are more compatible with cis than with trans DNA cleavage. These Int results either argue against a common mode of active-site assembly within the Int family or challenge the validity of Flp half sites as mimics of the normal full-site substrates. We devised a strategy to assay catalytic complementation between Flp monomers in full sites. We found that the full-site reaction follows the shared active-site paradigm and the trans mode of DNA cleavage. These results suggest that within the Int family, a unitary chemical mechanism of recombination is achieved by more than one mode of physical interaction among the recombinase monomers.
11
Whang, I., J. Lee, and M. Jayaram. "Active-site assembly and mode of DNA cleavage by Flp recombinase during full-site recombination." Molecular and Cellular Biology 14, no. 11 (November 1994): 7492–98. http://dx.doi.org/10.1128/mcb.14.11.7492-7498.1994.
Full textAbstract:
A combination of half-site substrates and step arrest mutants of Flp, a site-specific recombinase of the integrase family, had earlier revealed the following features of the half-site recombination reaction. (i) The Flp active site is assembled by sharing of catalytic residues from at least two monomers of the protein. (ii) A Flp monomer does not cleave the half site to which it is bound (DNA cleavage in cis); rather, it cleaves a half site bound by a second Flp monomer (DNA cleavage in trans). For the lambda integrase (Int protein), the prototype member of the Int family, catalytic complementation between two active-site mutants has been observed in reactions with a suicide attL substrate. By analogy with Flp, this observation is strongly suggestive of a shared active site and of trans DNA cleavage. However, reactions with linear suicide attB substrates and synthetic Holliday junctions are more compatible with cis than with trans DNA cleavage. These Int results either argue against a common mode of active-site assembly within the Int family or challenge the validity of Flp half sites as mimics of the normal full-site substrates. We devised a strategy to assay catalytic complementation between Flp monomers in full sites. We found that the full-site reaction follows the shared active-site paradigm and the trans mode of DNA cleavage. These results suggest that within the Int family, a unitary chemical mechanism of recombination is achieved by more than one mode of physical interaction among the recombinase monomers.
12
Shinzawa-Itoh, Kyoko, Takashi Sugimura, Tomonori Misaki, Yoshiki Tadehara, Shogo Yamamoto, Makoto Hanada, Naomine Yano, et al. "Monomeric structure of an active form of bovine cytochrome c oxidase." Proceedings of the National Academy of Sciences 116, no. 40 (September 18, 2019): 19945–51. http://dx.doi.org/10.1073/pnas.1907183116.
Full textAbstract:
Cytochrome c oxidase (CcO), a membrane enzyme in the respiratory chain, catalyzes oxygen reduction by coupling electron and proton transfer through the enzyme with a proton pump across the membrane. In all crystals reported to date, bovine CcO exists as a dimer with the same intermonomer contacts, whereas CcOs and related enzymes from prokaryotes exist as monomers. Recent structural analyses of the mitochondrial respiratory supercomplex revealed that CcO monomer associates with complex I and complex III, indicating that the monomeric state is functionally important. In this study, we prepared monomeric and dimeric bovine CcO, stabilized using amphipol, and showed that the monomer had high activity. In addition, using a newly synthesized detergent, we determined the oxidized and reduced structures of monomer with resolutions of 1.85 and 1.95 Å, respectively. Structural comparison of the monomer and dimer revealed that a hydrogen bond network of water molecules is formed at the entry surface of the proton transfer pathway, termed the K-pathway, in monomeric CcO, whereas this network is altered in dimeric CcO. Based on these results, we propose that the monomer is the activated form, whereas the dimer can be regarded as a physiological standby form in the mitochondrial membrane. We also determined phospholipid structures based on electron density together with the anomalous scattering effect of phosphorus atoms. Two cardiolipins are found at the interface region of the supercomplex. We discuss formation of the monomeric CcO, dimeric CcO, and supercomplex, as well as their role in regulation of CcO activity.
13
Zuo, Yuhong, and Murray P. Deutscher. "Mechanism of Action of RNase T." Journal of Biological Chemistry 277, no. 51 (October 2, 2002): 50160–64. http://dx.doi.org/10.1074/jbc.m207707200.
Full textAbstract:
A detailed structural and functional model ofE. coliRNase T was generated based on sequence analysis, homology modeling, and experimental observation. In the accompanying article, three short sequence segments (nucleic acid binding sequences (NBS)) important for RNase T substrate binding were identified. In the model, these segments cluster to form a positively charged surface patch. However, this patch is on the face of the RNase T monomer opposite the DEDD catalytic center. We propose that by dimerization, the NBS patch from one subunit is brought to the vicinity of the DEDD center of the second monomer to form a fully functional RNase T active site. In support of this model, mutagenetic studies show that one NBS1 residue, Arg13, sits at the catalytic center despite being on the opposite side of the monomer. Second, the complementarity of the RNase T subunits through the formation of homodimers was demonstrated by reconstitution of partial RNase T activity from monomers derived from two inactive mutant proteins, one defective in catalysis and one in substrate binding. These data explain why RNase T must dimerize to function. The model provides a detailed framework on which to explain the mechanism of action of RNase T.
14
Rozenberg, Boris A. "Vinyl monomers containing active hydrogen atoms are a new type of monomer for polycondensation." Macromolecular Symposia 199, no. 1 (October 2003): 443–54. http://dx.doi.org/10.1002/masy.200350937.
Full text
15
Beigneux, Anne P., Christopher M. Allan, Norma P. Sandoval, Geoffrey W. Cho, Patrick J. Heizer, Rachel S. Jung, Kimber L. Stanhope, et al. "Lipoprotein lipase is active as a monomer." Proceedings of the National Academy of Sciences 116, no. 13 (March 8, 2019): 6319–28. http://dx.doi.org/10.1073/pnas.1900983116.
Full textAbstract:
Lipoprotein lipase (LPL), the enzyme that hydrolyzes triglycerides in plasma lipoproteins, is assumed to be active only as a homodimer. In support of this idea, several groups have reported that the size of LPL, as measured by density gradient ultracentrifugation, is ∼110 kDa, twice the size of LPL monomers (∼55 kDa). Of note, however, in those studies the LPL had been incubated with heparin, a polyanionic substance that binds and stabilizes LPL. Here we revisited the assumption that LPL is active only as a homodimer. When freshly secreted human LPL (or purified preparations of LPL) was subjected to density gradient ultracentrifugation (in the absence of heparin), LPL mass and activity peaks exhibited the size expected of monomers (near the 66-kDa albumin standard). GPIHBP1-bound LPL also exhibited the size expected for a monomer. In the presence of heparin, LPL size increased, overlapping with a 97.2-kDa standard. We also used density gradient ultracentrifugation to characterize the LPL within the high-salt and low-salt peaks from a heparin-Sepharose column. The catalytically active LPL within the high-salt peak exhibited the size of monomers, whereas most of the inactive LPL in the low-salt peak was at the bottom of the tube (in aggregates). Consistent with those findings, the LPL in the low-salt peak, but not that in the high-salt peak, was easily detectable with single mAb sandwich ELISAs, in which LPL is captured and detected with the same antibody. We conclude that catalytically active LPL can exist in a monomeric state.
16
LUQUE, J. J., V. MAESTRO, A. LÓZAR, and A. CÓRDOBA. "TRANSIENT ORDERED STATES IN A MODEL REACTION ON A SURFACE WITH ACTIVE SITES." International Journal of Modern Physics C 14, no. 02 (February 2003): 159–67. http://dx.doi.org/10.1142/s0129183103004358.
Full textAbstract:
A model for the monomer–monomer surface reaction of the type A + B → AB, with diffusion of A and B monomers on a surface and reaction only on active sites randomly distributed on the surface, has been proposed and studied. For a critical point where both adsorption probabilities are the same, a seemingly reactive steady state transforms itself into a poisoned state. In this transient state, the production of AB molecules, in relation to the density of active sites, is considered and an inert-reactive irreversible phase transition is observed. The critical values of the density of active sites, where the irreversible phase transition occurs, is obtained in the limit L → ∞ by means of a finite-size scaling analysis. The critical exponents that dominate the correlation length of clusters, as well as the production of AB molecules at criticality, are determined.
17
Lindås, Ann-Christin, Maksymilian Chruszcz, Rolf Bernander, and Karin Valegård. "Structure of crenactin, an archaeal actin homologue active at 90°C." Acta Crystallographica Section D Biological Crystallography 70, no. 2 (January 30, 2014): 492–500. http://dx.doi.org/10.1107/s1399004714000935.
Full textAbstract:
The crystal structure of the archaeal actin, crenactin, from the rod-shaped hyperthermophilic (optimal growth at 90°C) crenarchaeonPyrobaculum calidifontisis reported at 3.35 Å resolution. Despite low amino-acid sequence identity, the three-dimensional structure of the protein monomer is highly similar to those of eukaryotic actin and the bacterial MreB protein. Crenactin-specific features are also evident, as well as elements that are shared between crenactin and eukaryotic actin but are not found in MreB. In the crystal, crenactin monomers form right-handed helices, demonstrating that the protein is capable of forming filament-like structures. Monomer interactions in the helix, as well as interactions between crenactin and ADP in the nucleotide-binding pocket, are resolved at the atomic level and compared with those of actin and MreB. The results provide insights into the structural and functional properties of a heat-stable archaeal actin and contribute to the understanding of the evolution of actin-family proteins in the three domains of life.
18
Zenin, V. A., E. G. Sadykhov, and A. N. Fedorov. "Dimerization of the Antimicrobial Peptide Polyphemusin I into One Polypeptide Chain: Theoretical and Practical Consequences." Biotekhnologiya 35, no. 5 (2019): 36–41. http://dx.doi.org/10.21519/0234-2758-2019-35-5-36-41.
Full textAbstract:
A strategy of sequential dimerization of monomers of antimicrobial peptides (AMPs) into one polypeptide chain has been implemented on the example of a beta-structural AMP polyphemusin I which is one of the most effective candidate for use as an antibiotic. The possible polyphemusin I monomer and dimer structures in lipid membrane were studied in this work via molecular modeling. To this end, these molecules were chemically synthesized so that the dimer represented two monomers connected in series into one polypeptide chain with a flexible linker. The antimicrobial effects of monomer and dimer were then tested on various bacterial cultures, and their similarity was shown. Therefore, we can conclude that the pore formation is not a putative mechanism of the polyphemusin I action. antimicrobial peptides, peptide dimerization, mechanism of antimicrobial action, polyphemusin The work was supported by the Ministry of Science and Higher Education of the Russian Federation (Project Unique Identifier RFMEFI57517X0151).
19
Nagai, Katsutoshi, Hiroshi Satoh, and Noriyuki Kuramoto. "Polymerization of surface-active monomers: 7. Radical copolymerizations of anionic surface-active monomer, sodium di(10-undecenyl)sulfosuccinate, with electron-accepting monomers and vinyl monomers in micellar and isotropic solutions." Polymer 34, no. 23 (January 1993): 4969–73. http://dx.doi.org/10.1016/0032-3861(93)90028-9.
Full text
20
Deng, Xiaobo, Shunsheng Cao, Bailing Liu, and Songjun Li. "Thermodynamic and Kinetic Considerations - Effect of Organic Siloxane on MMA Polymerization." Polymers and Polymer Composites 13, no. 5 (July 2005): 505–12. http://dx.doi.org/10.1177/096739110501300507.
Full textAbstract:
The effects of 3-(methacryloxypropyl)-trimethoxysilane (MATS) and vinyl trimethoxysilane (VTMOS) on methyl methacrylate (MMA) polymerization have been investigated. The two co-monomers appear to show opposite effects. The polymerization shows a higher rate of polymerization and extent of conversion in the presence of MATS than in its absence. However, a lower rate of polymerization and extent of conversion are obtained in the presence of VTMOS. The difference can be related to the different roles of the co-monomers. The increase in the rate of polymerization and conversion with MATS can be attributed to the higher reactivity of monomers. The lower conversion with VTMOS may be due to the electronic effects associated with VTMOS, which can decrease the electric density of the active double bond in MMA and therefore deactivate the polymerization. Further investigation shows that the change of free energy in the polymerization with MATS is lower than without MATS. Also, monomer reactivity in the presence of MATS is higher than in the absence of MATS. The decrease in free energy may be a thermodynamic response to the increase in the conversion. The increase in monomer reactivity may be responsible for increasing the rate of polymerization.
21
Mills-Davies, N., D. Butler, E. Norton, D. Thompson, M. Sarwar, J. Guo, R. Gill, et al. "Structural studies of substrate and product complexes of 5-aminolaevulinic acid dehydratase from humans,Escherichia coliand the hyperthermophilePyrobaculum calidifontis." Acta Crystallographica Section D Structural Biology 73, no. 1 (January 1, 2017): 9–21. http://dx.doi.org/10.1107/s2059798316019525.
Full textAbstract:
A number of X-ray analyses of an enzyme involved in a key early stage of tetrapyrrole biosynthesis are reported. Two structures of human 5-aminolaevulinate dehydratase (ALAD), native and recombinant, have been determined at 2.8 Å resolution, showing that the enzyme adopts an octameric quaternary structure in accord with previously published analyses of the enzyme from a range of other species. However, this is in contrast to the finding that a disease-related F12L mutant of the human enzyme uniquely forms hexamers [Breiniget al.(2003),Nature Struct. Biol.10, 757–763]. Monomers of all ALADs adopt the TIM-barrel fold; the subunit conformation that assembles into the octamer includes the N-terminal tail of one monomer curled around the (α/β)8barrel of a neighbouring monomer. Both crystal forms of the human enzyme possess two monomers per asymmetric unit, termedAandB. In the native enzyme there are a number of distinct structural differences between theAandBmonomers, with the latter exhibiting greater disorder in a number of loop regions and in the active site. In contrast, the second monomer of the recombinant enzyme appears to be better defined and the active site of both monomers clearly possesses a zinc ion which is bound by three conserved cysteine residues. In native human ALAD, theAmonomer also has a ligand resembling the substrate ALA which is covalently bound by a Schiff base to one of the active-site lysines (Lys252) and is held in place by an ordered active-site loop. In contrast, these features of the active-site structure are disordered or absent in theBsubunit of the native human enzyme. The octameric structure of the zinc-dependent ALAD from the hyperthermophilePyrobaculum calidifontisis also reported at a somewhat lower resolution of 3.5 Å. Finally, the details are presented of a high-resolution structure of theEscherichia coliALAD enzyme co-crystallized with a noncovalently bound moiety of the product, porphobilinogen (PBG). This structure reveals that the pyrrole side-chain amino group is datively bound to the active-site zinc ion and that the PBG carboxylates interact with the enzymeviahydrogen bonds and salt bridges with invariant residues. A number of hydrogen-bond interactions that were previously observed in the structure of yeast ALAD with a cyclic intermediate resembling the product PBG appear to be weaker in the new structure, suggesting that these interactions are only optimal in the transition state.
22
Iadrat, Ploychanok, and Chularat Wattanakit. "Bioethanol Upgrading to Renewable Monomers Using Hierarchical Zeolites: Catalyst Preparation, Characterization, and Catalytic Studies." Catalysts 11, no. 10 (September 26, 2021): 1162. http://dx.doi.org/10.3390/catal11101162.
Full textAbstract:
Bioethanol is one of the most promising renewable resources for the production of important monomers. To date, there have been various processes proposed for bioethanol conversion to renewable monomers. In this review, the catalytic bioethanol upgrading to various types of monomers using hierarchical zeolites as catalysts is illustrated, including the recent design and preparation of hierarchical zeolites for these catalytic processes. The characterizations of catalysts including textural properties, pore architectures, acidic properties, and active species are also exemplified. Moreover, the catalytic studies with various processes of monomer production from bioethanol including bioethanol dehydration, bioethanol to hydrocarbons, and bioethanol to butadiene are revealed in terms of catalytic activities and mechanistic studies. In addition, the future perspectives of these catalytic circumstances are proposed in both economic and sustainable development contexts.
23
Karasawa, Akira, Keiji Mitsui, Masafumi Matsushita, and Hiroshi Kanazawa. "Intermolecular cross-linking of monomers in Helicobacter pylori Na+/H+ antiporter NhaA at the dimer interface inhibits antiporter activity." Biochemical Journal 426, no. 1 (January 27, 2010): 99–108. http://dx.doi.org/10.1042/bj20091339.
Full textAbstract:
We have previously shown that HPNhaA (Helicobacter pylori Na+/H+ antiporter) forms an oligomer in a native membrane of Escherichia coli, and conformational changes of oligomer occur between monomers of the oligomer during ion transport. In the present study, we use Blue-native PAGE to show that HPNhaA forms a dimer. Cysteine-scanning mutagenesis of residues 55–61 in a putative β-sheet region of loop1 and subsequent functional analyses revealed that the Q58C mutation resulted in an intermolecular disulfide bond. G56C, I59C and G60C were found to be cross-linked by bifunctional cross-linkers. Furthermore, the Q58E mutant did not form a dimer, possibly due to electrostatic repulsion between monomers. These results imply that Gln-58 and the flanking sequence in the putative β-sheet of the monomer are located close to the identical residues in the dimer. The Q58C mutant of NhaA was almost inactive under non-reducing conditions, and activity was restored under reducing conditions. This result showed that cross-linking at the dimer interface reduces transporter activity by interfering with the flexible association between the monomers. A mutant HPNhaA protein with three amino acid substitutions at residues 57–59 did not form a dimer, and yet was active, indicating that the monomer is functional.
24
Shaw, A., P. A. Fortes, C. D. Stout, and V. D. Vacquier. "Crystal structure and subunit dynamics of the abalone sperm lysin dimer: egg envelopes dissociate dimers, the monomer is the active species." Journal of Cell Biology 130, no. 5 (September 1, 1995): 1117–25. http://dx.doi.org/10.1083/jcb.130.5.1117.
Full textAbstract:
Lysin is a 16-kD acrosomal protein used by abalone spermatozoa to create a hole in the egg vitelline envelope (VE) by a nonenzymatic mechanism. The crystal structure of the lysin monomer is known at 1.9 A resolution. The surface of the molecule reveals two tracks of basic residues running the length of one surface of the molecule and a patch of solvent-exposed hydrophobic residues on the opposite surface. Here we report that lysin dimerizes via interaction of the hydrophobic patches of monomers. Triton X-100 dissociates the dimer. The crystal structure of the dimer is described at 2.75 A resolution. Fluorescence energy transfer experiments show that the dimer has an approximate KD of 1 microM and that monomers exchange rapidly between dimers. Addition of isolated egg VE dissociates dimers, implicating monomers as the active species in the dissolution reaction. This work represents the first step in the elucidation of the mechanism by which lysin enables abalone spermatozoa to create a hole in the egg envelope during fertilization.
25
Khan, Sarfaraz, Huaili Zheng, Qiang Sun, Yongzhi Liu, Hong Li, Wei Ding, and Andrea Navarro. "Analysis of Influencing Factors for Leaching of Acrylamide Monomer from Polyacrylamide-Based Flocculants Used in the Treatment of Sludge Dewatering." Sensor Letters 18, no. 2 (February 1, 2020): 128–32. http://dx.doi.org/10.1166/sl.2020.4194.
Full textAbstract:
Acrylamide (AM) monomer is one of the harmful type substance, are commonly using to produce polyacrylamide (PAMs) flocculants for water treatment. Because of incomplete polymerization, the molecules of AM monomers also in exit marketable polymers. Therefore, discharge of AM from the usage of PAM based polymers flocculants in to environment. Currently study focus on, the AM leaching behaviour (emulsion and powder) polymer produced by two different production processes was studied with WTP sludge dewatering as the research object. The flocculants type's effects, Concentration of sludge and dosage on the discharge of AM residual monomer in sludge dewatering effluent were studied. The powder form flocculants results show, the regardless of the flocculants concentration and sludge concentration, the leaching concentration is not significant, but in the emulsion flocculants, the leaching concentration changes significantly. The Monomers of residual acrylamide be absorbed on the surface of sludge. Sludge concentration plays an active role in improving dehydration efficiency. Considering the trade-off between emulsion and powder polymer, the results of this study are related to the water treatment process.
26
Yeh, C. H., D. A. Hanna, G. W. Everett, and R. H. Himes. "Nuclear magnetic resonance relaxation studies of the interaction of ligands with the monomer and tetramer forms of formyltetrahydrofolate synthetase." Biochemical Journal 251, no. 1 (April 1, 1988): 89–93. http://dx.doi.org/10.1042/bj2510089.
Full textAbstract:
Previous work using n.m.r. spectroscopy to investigate the binding between formyltetrahydrofolate synthetase and its ligands was done using the catalytically active tetrameric form of the enzyme. By removal of specific monovalent cations the tetramer dissociates to four identical, catalytically inactive monomers, which are capable of binding nucleotides with affinities similar to those obtained with the tetramer. In the studies reported here, we examined the interaction of metal-nucleotide, formate and monovalent cations with the monomer using n.m.r. relaxation measurements. We were able to demonstrate that formate binds to the monomer. The spin-lattice relaxation rate (1/T1) of the formate carbon in the monomer. M2+.ADP. formate complex is enhanced when Mg2+ is replaced by Mn2+. By assuming that the exchange of formate is not rate-limiting and that tau c of the monomer is the same as that of the tetramer, the distance between the Mn2+ and the formate carbon was calculated and found to be similar in the monomer and tetramer complexes. The spin-lattice relaxation rates of [13C]trimethylammonium ion (an inactive monovalent cation), [13C]methylammonium and [15N]ammonium ions (both active monovalent cations), were measured in the presence of tetramer, MnADP and formate. The relaxation rates of methylammonium and ammonium ions were enhanced under these conditions whereas the relaxation rate of trimethylammonium ion was not. The results indicate that the active monovalent cations bind near the MnADP binding site. A distance from the Mn2+ to the ammonium nitrogen of between 0.5 and 0.6 nm was calculated.
27
Guo, Wen Lu, Hong Chun Zhou, Han Qing Lu, and Wei Hu. "Preparation and Characterization of Fluorinated Epoxy Resin Emulsion for Waterborne Coatings." Advanced Materials Research 347-353 (October 2011): 4065–68. http://dx.doi.org/10.4028/www.scientific.net/amr.347-353.4065.
Full textAbstract:
Under the action of initiator(BPO), the α-methyl acrylic acid (α-MAA), butyl hexafluorobutyl methacrylate (HFMA) and other monomers are graft copolymerized into epoxy molecular. By adding N, N-dimethyl ethanolamine, fluorine-containing water-based epoxy resin emulsion can be prepared. By orthogonal experiments, the amount of acrylic monomer, BPO dosage, grafting temperature and other optimum conditions can be determined. Infrared spectroscopy (FT-IR) characterization confirms acrylic monomers successfully grafted to the epoxy resin molecules. The study focuses on the effect of different content of HFMA on modified emulsion particle size and contact angle of coating. The results shows that the introduction of HFMA monomer made the smallest average particle size of emulsion low to 165 nm, and the contact angle against water is increased by 20°. After determining the conventional and environmental performance of the emulsion, the results shows that this preparation of epoxy resin emulsion can fully meet the requirements of waterborne coatings.
28
Ponce-Coria, José, Kenneth B. Gagnon, and Eric Delpire. "Calcium-binding protein 39 facilitates molecular interaction between Ste20p proline alanine-rich kinase and oxidative stress response 1 monomers." American Journal of Physiology-Cell Physiology 303, no. 11 (December 1, 2012): C1198—C1205. http://dx.doi.org/10.1152/ajpcell.00284.2012.
Full textAbstract:
X-ray crystallography of the catalytic domain of oxidative stress response 1 (OSR1) has provided evidence for dimerization and domain swapping. However, the functional significance of dimer formation or domain swapping has yet to be addressed. In this study, we used nine glutamine residues to link the carboxyl end of one SPAK (related Ste20 kinase) monomer to the amino end of another SPAK monomer to assess the role of kinase monomers versus dimers in Na-K-2Cl cotransporter 1 (NKCC1) activation. Transport studies in Xenopus laevis oocytes show that forcing dimerization of two wild-type SPAK molecules results in cotransporter activation when calcium-binding protein 39 (Cab39) is coexpressed, indicating that the presence of Cab39 can bypass the upstream phosphorylation requirement of SPAK normally associated with kinase activation. We determined that monomers are the functional units of the kinase as concatamers consisting of an active and various inactive monomers were still functional. Furthermore, we found that two different nonfunctional SPAK mutants could be linked together in a concatamer and activated, presumably by domain swapping, indicating that dimerization and domain swapping are both important components of kinase activation. Finally, we demonstrate rescue of a nonfunctional SPAK mutant by domain swapping with wild-type OSR1, indicating that heterodimers of the two Ste20-related kinases are possible and therefore potentially relevant to the regulation of NKCC1 activity.
29
Opri, Mirela, Emilia Amzoiu, Horia Octavian Manolea, and Radu Rîcă. "Computational Study of Physicochemical Properties of the Monomers Used in Stomatology." Key Engineering Materials 695 (May 2016): 59–64. http://dx.doi.org/10.4028/www.scientific.net/kem.695.59.
Full textAbstract:
Monomers used in dentistry allow tackling shrinkage problem during polymerization of dental composites.These monomers may cross biomembranes, a phenomenon that can lead to various toxic responses. An important factor that express the lipophilicity of these compounds is the partition coefficient. This parameter allows assessment of the solubility of a monomer to another and, generally, of a material to another.Computational partition coefficients study of water / octanol for a series of monomeric compounds analyzed showed the contribution of chemical structures dependent descriptors of substances on this parameter. The purpose of the assessment of these molecular descriptors is to show their importance in the partition of the substances studied in two phases aqueous and lipid (n-octanol).This allows optimization of the action of compounds activity very useful in finding new monomers used in dental reconstruction.
30
Sawant, Kirti V., Renling Xu, Robert Cox, Hal Hawkins, Elena Sbrana, Deepthi Kolli, Roberto P. Garofalo, and Krishna Rajarathnam. "Chemokine CXCL1-Mediated Neutrophil Trafficking in the Lung: Role of CXCR2 Activation." Journal of Innate Immunity 7, no. 6 (2015): 647–58. http://dx.doi.org/10.1159/000430914.
Full textAbstract:
The chemokine CXCL1 and its receptor CXCR2 play a crucial role in host immune response by recruiting and activating neutrophils for microbial killing at the tissue site. Dysregulation in this process has been implicated in collateral tissue damage causing disease. CXCL1 reversibly exists as monomers and dimers, and it has been proposed that distinct monomer and dimer activities and the monomer-dimer equilibrium regulate the neutrophil function. However, the molecular mechanisms linking the CXCL1/CXCR2 axis and the neutrophil ‘beneficial' and ‘destructive' phenotypes are not known. In this study, we characterized neutrophil trafficking and its consequence in the mouse lung by the CXCL1 wild type (WT), which exists as monomers and dimers, and by a nondissociating dimer. Whereas the WT, compared to the dimer, was more active at low doses, both the WT and the dimer elicited a large neutrophil efflux at high doses. Importantly, robust neutrophil recruitment elicited by the WT or dimer was not detrimental to lung tissue integrity and, further, could not be correlated to surface CXCR2 levels. We conclude that the CXCL1 monomer-dimer distribution and receptor interactions are highly coupled and regulate neutrophil trafficking and that injury in the context of disease is a consequence of inappropriate CXCR2 activation at the target tissue and not due to mechanical forces exerted by neutrophils during recruitment.
31
Landree, Mark A., Sam B. Kale, and David B. Roth. "Functional Organization of Single and Paired V(D)J Cleavage Complexes." Molecular and Cellular Biology 21, no. 13 (July 1, 2001): 4256–64. http://dx.doi.org/10.1128/mcb.21.13.4256-4264.2001.
Full textAbstract:
ABSTRACT RAG-1 and RAG-2 initiate V(D)J recombination by binding to specific recognition sequences (RSS) and then cleave the DNA in two steps: nicking and hairpin formation. Recent work has established that a dimer of RAG-1 and either one or two monomers of RAG-2 bind to a single RSS, but the enzymatic contributions of the RAG molecules within this nucleoprotein complex and its functional organization have not been elucidated. Using heterodimeric protein preparations containing both wild-type and catalytically deficient RAG-1 molecules, we found that one active monomer is sufficient for both nicking and hairpin formation at a single RSS, demonstrating that a single active site can carry out both cleavage steps. Furthermore, the mutant heterodimers efficiently cleaved both RSS in a synaptic complex. These results strongly suggest that two RAG-1 dimers are responsible for RSS cleavage in a synaptic complex, with one monomer of each dimer catalyzing both nicking and hairpin formation at each RSS.
32
Kuang, Jia, Nan Zheng, Chenglin Liu, and Yubin Zheng. "Manipulating the thermal and dynamic mechanical properties of polydicyclopentadiene via tuning the stiffness of the incorporated monomers." e-Polymers 19, no. 1 (May 29, 2019): 355–64. http://dx.doi.org/10.1515/epoly-2019-0037.
Full textAbstract:
AbstractThe application of polydicyclopentadiene (polyDCPD) as a high-performance thermosetting resin is often hindered by the simplicity and limitation of the polymer structure, making it unlikely to improve their thermal and dynamic mechanical properties by further optimizing the polymerization conditions. In this study, we developed a copolymer system which consisted of dicyclo-pentadienes and various designed monomers as excellent curing agents. The incorporated monomers bearing different stiffness and rigidity contain two active functional groups at the end of the structures and are capable of reinforcing original polyDCPD. The incorporated monomers notably enhanced the thermal and dynamic mechanical properties of polyDCPD. Besides that, the relationship between the stiffness of the monomer and the thermal and dynamic mechanical properties of polyDCPD was evaluated in detailed. Because of the simplicity and adjustability of copolymerization approach, optimal conditions of the copolymers with best property-reinforcing capability were systemically identified. The optimal materials displayed desired thermal and dynamic mechanical property and markedly outperformed the original polyDCPD.
33
Jitonnom, Jitrayut, and Wijitra Meelua. "Cationic ring-opening polymerization of cyclic carbonates and lactones by group 4 metallocenes: A theoretical study on mechanism and ring-strain effects." Journal of Theoretical and Computational Chemistry 16, no. 01 (February 2017): 1750003. http://dx.doi.org/10.1142/s0219633617500031.
Full textAbstract:
Group 4 metallocene-mediated cationic ring-opening polymerizations of a series of lactones and cyclic carbonates, with different ring sizes ([Formula: see text]–8) have been theoretically studied. Using the “naked cation” approach in combination with density functional theory, the activated chain-end mechanism and the influence of transition metals, solvent and monomer ring size on the polymerizability were explored in detail. The results showed that the cationic metallocene–monomer complex, [catalyst][monomer][Formula: see text], is formed, generating cationic (carbocation ion) species responsible for polymer chain growth. We found that poor polymerizability of five-membered lactone and six-membered ring carbonate depends not only on the nature of the monomer ring size but also the relative stability of the complex, which was found to correlate well with the ring strain. Subsequently, several propagation steps take place through an SN2 reaction which involves ring opening of an active monomer, via alkyl–oxygen bond cleavage. Based on the computed activation energies of all metallocene systems, the first propagation was found to be the rate-determining step of the overall propagation and the hafnocene was found to be most active with the energy barrier of 17.6[Formula: see text]kcal/mol, followed by zirconocene (18.6[Formula: see text]kcal/mol) and titanocene (19.5[Formula: see text]kcal/mol), respectively. The mechanistic study may be applicable to the cationic ROP of lactides and other related monomers.
34
Ferreira, J. P. M., R. Sasisekharan, O. Louie, and R. Langer. "A study on the functional subunits of phospholipases A2 by enzyme immobilization." Biochemical Journal 303, no. 2 (October 15, 1994): 527–30. http://dx.doi.org/10.1042/bj3030527.
Full textAbstract:
Pancreatic and venom phospholipases A2 have complex and distinct oligomerization behaviour. Pancreatic enzymes are monomeric in solution, but their quaternary structure at interfaces is unknown. On the other hand, certain crotalid venom phospholipases A2 are dimeric in solution, and different reports have proposed either the monomer or the dimer as the catalytically functional subunit. In this study, enzyme immobilization was used as a tool for determining the functional subunits of these enzymes. The dimeric Crotalus atrox phospholipase A2 was covalently attached to agarose beads, via either the amine or the carboxylic groups of the protein. In the first case immobilization led to an 80% loss of activity as compared with the soluble form, and measured by using micellar diheptanoylphosphocholine. Inclusion of micellar protectants in the coupling media did not improve the activity. Enzyme immobilized via carboxylic groups was 2-3-fold more active than the amine-coupled form. In a second approach, Crotalus atrox enzyme was immobilized with single-subunit attachment. The removal, with denaturating washes, of the non-covalently bound units involved in monomer-monomer interactions, caused a large decrease in specific activity of the support-bound enzyme. This suggests the dimeric form as the fully active one. Similar procedures were also carried out with pig pancreatic and Naja naja phospholipases A2. The results indicated that these enzymes are active as monomers.
35
Xin, Xiu Lan, Xue Han, and Qiong Hua Jin. "Synthesis of Spiropyran Photochromic Polymer." Advanced Materials Research 380 (November 2011): 64–68. http://dx.doi.org/10.4028/www.scientific.net/amr.380.64.
Full textAbstract:
Photochromic spiropyran material is of the most extensive and in-depth category. Small molecule spiropyran ring by UV irradiation, the color is less stable body, which restricts the widespread use of these compounds. In this paper, the introduction of spiropyran compounds with substituents on the group method of open-loop stability, which will contain active groups spiropyran monomers in the polymer side chain connected to a rigid polymer to limit the use of spiropyran ring merocyanine body rotation, so that the body color is more stable. This selection and design of the process is simple with R = CH2OCOC (CH3) =CH2 groups spiropyran monomer compounds, and then with methyl methacrylate polymer formed by radical means. By IR, NMR spectroscopy, mass spectrometry and gel permeation chromatography of the target compounds were characterized. UV spectrometer using the compounds of new photochromic properties were tested and the results shows spiropyran monomers and polymers have good photochromic properties. Discoloration kinetic of the spiropyran monomers and polymers in polar solvents proved to the spiropyran side connected to the polymer chain can significantly improve the stability of the color body.
36
Zhao, Hong Kai, Li Guang Xiao, and Jing Wu Gao. "Research of Interface of Carbon Fiber Reinforced PA6 by In-Situ Anionic Polymerization." Advanced Materials Research 634-638 (January 2013): 2028–31. http://dx.doi.org/10.4028/www.scientific.net/amr.634-638.2028.
Full textAbstract:
High polymer active functional groups can be grafted on the surface of carbon fibers so as to adjust the interface effect between fibers in the composite material and resin and improve the performance of composite material, by controlling the structure of grafted high polymer, the interface layer with intended performance can be well designed. Heat treatment does not affect the fiber strength, the content of functional groups on the surface of the fibers reaches the max. value around 1h. There are no macromolecules polymerized and grafted on the surface of carbon fibers not subjected to isocyanate grafting treatment. Through isocyanate treatment after heat treatment, it can be obviously seen that the nylon molecules are grafted on the fiber surface. When no activating agent is added in the polymerized monomers, the resin grafting percent of fiber surface can reach 18.8%; when 0.003 activating agent (mole ratio of it to monomers) is added in the monomers, the grafting percent of PA6 on surface of carbon fibers is only 7.65%, this is the result of reactive competition on the interface between monomer matrix and fibers.
37
MARTZ, Françoise, Malgorzata WILCZYNSKA, and Leszek A. KLECZKOWSKI. "Oligomerization status, with the monomer as active species, defines catalytic efficiency of UDP-glucose pyrophosphorylase." Biochemical Journal 367, no. 1 (October 1, 2002): 295–300. http://dx.doi.org/10.1042/bj20020772.
Full textAbstract:
Barley UDP-glucose pyrophosphorylase (UGPase), a key enzyme for the synthesis of sucrose, cellulose and other saccharides, was expressed in Escherichia coli and purified. Using both native electrophoresis and gel filtration, the recombinant and crude leaf UGPase proteins were found to exist as a mixture of monomers, dimers and higher-order polymers. In order to understand the molecular basis for the oligomerization of UGPase, a conserved Cys residue was replaced (C99S mutant) and several amino acids were substituted (LIV to NIN, KK to LL and LLL to NNN) in a conserved hydrophobic domain (amino acids 117—138). The C99S mutant had about half the Vmax of the wild-type and a 12-fold higher Km for PPi, whereas NIN and LL mutations lowered the Vmax by 12- and 2-fold, respectively, with relatively small effects on substrate Km values (the NNN mutant was insoluble/inactive). The NIN mutation resulted in a low-activity oligomerized enzyme form, with very little monomer formation. Activity staining on native PAGE gels as well as gel-filtration studies demonstrated that the monomer was the sole enzymically active form. Possible implications of the oligomerization status of UGPase for post-translational regulation of the enzyme are discussed.
38
Chiu, Hsiu-Ju, Joanna C. Grant, Carol L. Farr, Lukasz Jaroszewski, Mark W. Knuth, Mitchell D. Miller, Marc-André Elsliger, et al. "Structural analysis of arabinose-5-phosphate isomerase fromBacteroides fragilisand functional implications." Acta Crystallographica Section D Biological Crystallography 70, no. 10 (September 27, 2014): 2640–51. http://dx.doi.org/10.1107/s1399004714017052.
Full textAbstract:
The crystal structure of arabinose-5-phosphate isomerase (API) fromBacteroides fragilis(bfAPI) was determined at 1.7 Å resolution and was found to be a tetramer of a single-domain sugar isomerase (SIS) with an endogenous ligand, CMP-Kdo (cytidine 5′-monophosphate-3-deoxy-D-manno-oct-2-ulosonate), bound at the active site. API catalyzes the reversible isomerization of D-ribulose 5-phosphate to D-arabinose 5-phosphate in the first step of the Kdo biosynthetic pathway. Interestingly, the bound CMP-Kdo is neither the substrate nor the product of the reaction catalyzed by API, but corresponds to the end product in the Kdo biosynthetic pathway and presumably acts as a feedback inhibitor for bfAPI. The active site of each monomer is located in a surface cleft at the tetramer interface between three monomers and consists of His79 and His186 from two different adjacent monomers and a Ser/Thr-rich region, all of which are highly conserved across APIs. Structure and sequence analyses indicate that His79 and His186 may play important catalytic roles in the isomerization reaction. CMP-Kdo mimetics could therefore serve as potent and specific inhibitors of API and provide broad protection against many different bacterial infections.
39
Glazkov, S. S., D. S. Glazkov, V. A. Kozlov, and Y. F. Shutilin. "A model for producing polymer stabilizers of composites with a given macromolecule composition." Proceedings of the Voronezh State University of Engineering Technologies 82, no. 1 (May 15, 2020): 262–66. http://dx.doi.org/10.20914/2310-1202-2020-1-262-266.
Full textAbstract:
An attempt has been made to obtain a working technological formula that regulates the addition of comonomer over time, which ensures the synthesis of a copolymer macromolecule with a constant composition and, accordingly, with predicted properties of both the copolymer and its modified porous composite materials. Mathematical modeling is based on the theory of the kinetics of copolymerization, which takes into account the reactivity of monomers by means of copolymerization constants of reacting comonomers. The starting base was the kinetics of the copolymerization of two comonomers, significantly differing in their reactivity, which required a sequential, stepwise supply of a less reactive monomer to the reaction medium with a more active monomer. This technological technique contributes to maintaining the constancy of the initial ratio of comonomers and, accordingly, the synthesis of a copolymer with a constant composition, structure and properties. The dependence of the sequence of supply of comonomer to the reaction medium required the introduction of a generalized effective binary copolymerization rate coefficient. To find the generalized coefficient of the copolymerization rate, the operation of logarithm was performed and the current expression of the dependence of the concentration change of the more active monomer in time in a linear form was translated. This mathematical technique made it possible to use software to process reference information to obtain the necessary coefficients for the working formula. As a result of mathematical modeling using the basic principles of binary copolymerization, the law of effective masses, and the least squares method, a working formula is obtained that allows one to regulate the given introduction of a less active monomer into the reaction medium in time. The model is analyzed using background information, the basic concepts of binary copolymerization and can be used in technological calculations when producing copolymers with specified characteristics in composition and structure.
40
Bouchemal, K., S. Briançon, F. Couenne, H. Fessi, and M. Tayakout. "Stability Studies on Colloidal Suspensions of Polyurethane Nanocapsules." Journal of Nanoscience and Nanotechnology 6, no. 9 (September 1, 2006): 3187–92. http://dx.doi.org/10.1166/jnn.2006.468.
Full textAbstract:
Generally nanocapsules suspensions are a colloidal system in a metastable state, there is aggregation due to attraction and repulsion forces between particles. The objective of this work was to bring the role of the polymeric membrane in the protection of the active drug against damaging caused by external agents and to select the monomer which leads to obtain stable formulation with the highest possible payload of the active drug. The stability testing involving visual aspect, particle size measurement, transmission electron microscopy (TEM) examination, and drug loss was conduced after 6 months of storage at different temperatures (4, 25, and 45 °C). The colloidal suspensions of nanocapsules were obtained using the combined interfacial polycondensation and spontaneous emulsification, the technique was used to encapsulate α-tocopherol using polyurethanes polymers. It is a one step procedure: An organic phase composed of a water miscible solvent (acetone), lipophilic monomer (Isophorone diisocyanate IPDI), oil, and a lipophilic surfactant, is injected in an aqueous phase containing hydrophilic monomer (diol with various molecular weight: 1,2-ethanediol (ED), 1,4-butanediol (BD), and 1,6-hexanediol (HD)) and hydrophilic emulsifying agent. The water miscible solvent diffuses to the aqueous phase, the oil precipitates as nano-droplets, and the two monomers react at the interface, forming a membrane around the nanoemulsion leading to nanocapsules. A good physical stability of suspensions corresponds to absence of symptoms such as sedimentation or agglomeration, significant size change and α-tocopherol degradation due to external agents such as oxygen, temperature, and ultraviolet (UV) irradiation. The size of nanocapsules before storage was about 232±3, 258±29, and 312±4 nm for ED, BD, and HD, respectively. After 6 months of storage, polyurethanes nanocapsules possess good stability against aggregation at 4 and 25 °C. Comparing results obtained using different monomers, it reveals that the polyurethane based on HD offers good protection of α-tocopherol against damaging caused by the temperature and UV irradiation.
41
Phang, Juanita M., Stephen J. Harrop, Anthony P. Duff, Anna V. Sokolova, Ben Crossett, James C. Walsh, Simone A. Beckham, et al. "Structural characterization suggests models for monomeric and dimeric forms of full-length ezrin." Biochemical Journal 473, no. 18 (September 12, 2016): 2763–82. http://dx.doi.org/10.1042/bcj20160541.
Full textAbstract:
Ezrin is a member of the ERM (ezrin–radixin–moesin) family of proteins that have been conserved through metazoan evolution. These proteins have dormant and active forms, where the latter links the actin cytoskeleton to membranes. ERM proteins have three domains: an N-terminal FERM [band Four-point-one (4.1) ERM] domain comprising three subdomains (F1, F2, and F3); a helical domain; and a C-terminal actin-binding domain. In the dormant form, FERM and C-terminal domains form a stable complex. We have determined crystal structures of the active FERM domain and the dormant FERM:C-terminal domain complex of human ezrin. We observe a bistable array of phenylalanine residues in the core of subdomain F3 that is mobile in the active form and locked in the dormant form. As subdomain F3 is pivotal in binding membrane proteins and phospholipids, these transitions may facilitate activation and signaling. Full-length ezrin forms stable monomers and dimers. We used small-angle X-ray scattering to determine the solution structures of these species. As expected, the monomer shows a globular domain with a protruding helical coiled coil. The dimer shows an elongated dumbbell structure that is twice as long as the monomer. By aligning ERM sequences spanning metazoan evolution, we show that the central helical region is conserved, preserving the heptad repeat. Using this, we have built a dimer model where each monomer forms half of an elongated antiparallel coiled coil with domain-swapped FERM:C-terminal domain complexes at each end. The model suggests that ERM dimers may bind to actin in a parallel fashion.
42
Torres-Moya, Iván, Rebeca Vázquez-Guilló, Sara Fernández-Palacios, José Ramón Carrillo, Ángel Díaz-Ortiz, Juan Teodomiro López Navarrete, Rocío Ponce Ortiz, Mari Carmen Ruiz Delgado, Ricardo Mallavia, and Pilar Prieto. "Fluorene-Based Donor-Acceptor Copolymers Containing Functionalized Benzotriazole Units: Tunable Emission and their Electrical Properties." Polymers 12, no. 2 (January 22, 2020): 256. http://dx.doi.org/10.3390/polym12020256.
Full textAbstract:
Monomers 4,7-dibromo-2H-benzo[d]1,2,3-triazole (m1) and 4,7-(bis(4-bromophenyl)ethynyl)-2H-benzo[d]1,2,3-triazole (m2) have been synthesized in good yields using different procedures. Monomers m1 and m2 have been employed for building new copolymers of fluorene derivatives by a Suzuki reaction under microwave irradiation using the same conditions. In each case different chain lengths have been achieved, while m1 gives rise to polymers for m2 oligomers have been obtained (with a number of monomer units lower than 7). Special interest has been paid to their photophysical properties due to excited state properties of these D-A units alternates, which have been investigated by density functional theory (DFT) calculations using two methods: (i) An oligomer approach and (ii) by periodic boundary conditions (PBC). It is highly remarkable the tunability of the photophysical properties as a function of the different monomer functionalization derived from 2H-benzo[d]1,2,3-triazole units. In fact, a strong modulation of the absorption and emission properties have been found by functionalizing the nitrogen N-2 of the benzotriazole units or by elongation of the π-conjugated core with the introduction of alkynylphenyl groups. Furthermore, the charge transport properties of these newly synthesized macromolecules have been approached by their implementation in organic field-effect transistors (OFETs) in order to assess their potential as active materials in organic optoelectronics.
43
Banerjee, Puja, and Biman Bagchi. "Dynamical control by water at a molecular level in protein dimer association and dissociation." Proceedings of the National Academy of Sciences 117, no. 5 (January 22, 2020): 2302–8. http://dx.doi.org/10.1073/pnas.1908379117.
Full textAbstract:
Water, often termed as the “lubricant of life,” is expected to play an active role in navigating protein dissociation–association reactions. In order to unearth the molecular details, we first compute the free-energy surface (FES) of insulin dimer dissociation employing metadynamics simulation, and then carry out analyses of insulin dimerization and dissociation using atomistic molecular-dynamics simulation in explicit water. We select two sets of initial configurations from 1) the dissociated state and 2) the transition state, and follow time evolution using several long trajectories (∼1–2 μs). During the process we not only monitor configuration of protein monomers, but also the properties of water. Although the equilibrium structural properties of water between the two monomers approach bulklike characteristics at a separation distance of ∼5 nm, the dynamics differ considerably. The complex association process is observed to be accompanied by several structural and dynamical changes of the system, such as large-scale correlated water density fluctuations, coupled conformational fluctuation of protein monomers, a dewettinglike transition with the change of intermonomeric distance RMM from ∼4 to ∼2 nm, orientation of monomers and hydrophobic hydration in the monomers. A quasistable, solvent-shared, protein monomer pair (SSPMP) forms at around 2 nm during association process which is a local free-energy minimum having ∼50–60% of native contacts. Simulations starting with arrangements sampled from the transition state (TS) of the dimer dissociation reveal that the final outcome depends on relative orientation of the backbone in the “hotspot” region.
44
BLONG, M. Renee, Elliott BEDOWS, and Oksana LOCKRIDGE. "Tetramerization domain of human butyrylcholinesterase is at the C-terminus." Biochemical Journal 327, no. 3 (November 1, 1997): 747–57. http://dx.doi.org/10.1042/bj3270747.
Full textAbstract:
Butyrylcholinesterase (BChE) in human serum consists predominantly of tetramers. Recombinant BChE, however, expressed in Chinese hamster ovary (CHO) cells, consists of approx. 55% dimers, 10-30% tetramers and 15-40% monomers. To determine the origin of the monomer species we added the FLAG epitope (epitope tag, amino acid sequence DYKDDDDK) to the C-terminus of the enzyme, and expressed BChE-FLAG in CHO cells. We found that secreted, active monomers had lost their FLAG epitope, suggesting that the monomers were made by proteolysis of dimers or tetramers at the C-terminus. To estimate the number of amino acids that could be deleted from the C-terminus without losing BChE activity, we expressed deletion mutants. We found that deletion of up to 50 amino acids from the C-terminus yielded active monomers, but that deletion of 51 amino acids destroyed BChE activity and caused the inactive protein to remain within the cell. Deletion of eight or more amino acids from the N-terminus also resulted in inactive protein that remained inside the cell. Monomeric BChE had wild-type Km and kcat values (8 μM and 24000 min-1 for butyrylthiocholine) and showed substrate activation. The Cys-571→Ala mutant, though incapable of forming the interchain disulphide bond, had nearly the same amount of tetrameric BChE as recombinant wild-type BChE. These results support the conclusion that the tetramerization domain of BChE is at the C-terminus, within the terminal 50 amino acids, and that the interchain disulphide bond is not essential for tetramerization. Molecular modelling suggested that the tetramerization domain was a four-helix bundle, stabilized by interactions of seven conserved aromatic amino acids.
45
Solomon, Hodaya V., Orly Tabachnikov, Shifra Lansky, Rachel Salama, Hadar Feinberg, Yuval Shoham, and Gil Shoham. "Structure–function relationships in Gan42B, an intracellular GH42 β-galactosidase fromGeobacillus stearothermophilus." Acta Crystallographica Section D Biological Crystallography 71, no. 12 (November 26, 2015): 2433–48. http://dx.doi.org/10.1107/s1399004715018672.
Full textAbstract:
Geobacillus stearothermophilusT-6 is a Gram-positive thermophilic soil bacterium that contains a battery of degrading enzymes for the utilization of plant cell-wall polysaccharides, including xylan, arabinan and galactan. A 9.4 kb gene cluster has recently been characterized inG. stearothermophilusthat encodes a number of galactan-utilization elements. A key enzyme of this degradation system is Gan42B, an intracellular GH42 β-galactosidase capable of hydrolyzing short β-1,4-galactosaccharides into galactose units, making it of high potential for various biotechnological applications. The Gan42B monomer is made up of 686 amino acids, and based on sequence homology it was suggested that Glu323 is the catalytic nucleophile and Glu159 is the catalytic acid/base. In the current study, the detailed three-dimensional structure of wild-type Gan42B (at 2.45 Å resolution) and its catalytic mutant E323A (at 2.50 Å resolution), as determined by X-ray crystallography, are reported. These structures demonstrate that the three-dimensional structure of the Gan42B monomer generally correlates with the overall fold observed for GH42 proteins, consisting of three main domains: an N-terminal TIM-barrel domain, a smaller mixed α/β domain, and the smallest all-β domain at the C-terminus. The two catalytic residues are located in the TIM-barrel domain in a pocket-like active site such that their carboxylic functional groups are about 5.3 Å from each other, consistent with a retaining mechanism. The crystal structure demonstrates that Gan42B is a homotrimer, resembling a flowerpot in general shape, in which each monomer interacts with the other two to form a cone-shaped tunnel cavity in the centre. The cavity is ∼35 Å at the wide opening and ∼5 Å at the small opening and ∼40 Å in length. The active sites are situated at the interfaces between the monomers, so that every two neighbouring monomers participate in the formation of each of the three active sites of the trimer. They are located near the small opening of the cone tunnel, all facing the centre of the cavity. The biological relevance of this trimeric structure is supported by independent results obtained from gel-permeation chromatography. These data and their comparison to the structural data of related GH42 enzymes are used for a more general discussion concerning structure–activity aspects in this GH family.
46
Camacho, Inês S., Alina Theisen, Linus O. Johannissen, L. Aranzazú Díaz-Ramos, John M. Christie, Gareth I. Jenkins, Bruno Bellina, Perdita Barran, and Alex R. Jones. "Native mass spectrometry reveals the conformational diversity of the UVR8 photoreceptor." Proceedings of the National Academy of Sciences 116, no. 4 (January 4, 2019): 1116–25. http://dx.doi.org/10.1073/pnas.1813254116.
Full textAbstract:
UVR8 is a plant photoreceptor protein that regulates photomorphogenic and protective responses to UV light. The inactive, homodimeric state absorbs UV-B light, resulting in dissociation into monomers, which are considered to be the active state and comprise a β-propeller core domain and intrinsically disordered N- and C-terminal tails. The C terminus is required for functional binding to signaling partner COP1. To date, however, structural studies have only been conducted with the core domain where the terminal tails have been truncated. Here, we report structural investigations of full-length UVR8 using native ion mobility mass spectrometry adapted for photoactivation. We show that, while truncated UVR8 photoconverts from a single conformation of dimers to a single monomer conformation, the full-length protein exists in numerous conformational families. The full-length dimer adopts both a compact state and an extended state where the C terminus is primed for activation. In the monomer the extended C terminus destabilizes the core domain to produce highly extended yet stable conformations, which we propose are the fully active states that bind COP1. Our results reveal the conformational diversity of full-length UVR8. We also demonstrate the potential power of native mass spectrometry to probe functionally important structural dynamics of photoreceptor proteins throughout nature.
47
He, Xiao Zhi, Mei Tian, Yang Chen, Jing Zhao, and Bao Yan Zhang. "Chiral Liquid Crystal Polymers Containing Electron Donor- Acceptor Action-Synthesis and Characterization." Advanced Materials Research 284-286 (July 2011): 2284–87. http://dx.doi.org/10.4028/www.scientific.net/amr.284-286.2284.
Full textAbstract:
A series of new chiral side-chain liquid crystalline polymers with electron donor-acceptor action were prepared containing chiral monomer with donor group and nematic LC monomer with acceptor group. All polymers were synthesized by graft polymerization using polymethylhydro- siloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry(DSC), polarizing optical microscopy(POM)，thermogravimetric analyses（TGA） and X-ray diffraction measurements(XRD). The chemical structures of monomers and polymers were confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance spectra(1H NMR and 13CNMR). M1 showed nematic phase and M2 turned out cholesteric phase on heating and cooling cycle. Polymers P3~P8 were cholesteric phase. Experimental results demonstrated that the glass transition temperatures and isotropization temperatures and the ranges of the mesophase temperature increased with increasing the content of chiral agent. All of the obtained polymers showed high thermal stability.
48
Caiolfa, Valeria R., Moreno Zamai, Gabriele Malengo, Annapaola Andolfo, Chris D. Madsen, Jason Sutin, Michelle A. Digman, Enrico Gratton, Francesco Blasi, and Nicolai Sidenius. "Monomer–dimer dynamics and distribution of GPI-anchored uPAR are determined by cell surface protein assemblies." Journal of Cell Biology 179, no. 5 (December 3, 2007): 1067–82. http://dx.doi.org/10.1083/jcb.200702151.
Full textAbstract:
To search for functional links between glycosylphosphatidylinositol (GPI) protein monomer–oligomer exchange and membrane dynamics and confinement, we studied urokinase plasminogen activator (uPA) receptor (uPAR), a GPI receptor involved in the regulation of cell adhesion, migration, and proliferation. Using a functionally active fluorescent protein–uPAR in live cells, we analyzed the effect that extracellular matrix proteins and uPAR ligands have on uPAR dynamics and dimerization at the cell membrane. Vitronectin directs the recruitment of dimers and slows down the diffusion of the receptors at the basal membrane. The commitment to uPA–plasminogen activator inhibitor type 1–mediated endocytosis and recycling modifies uPAR diffusion and induces an exchange between uPAR monomers and dimers. This exchange is fully reversible. The data demonstrate that cell surface protein assemblies are important in regulating the dynamics and localization of uPAR at the cell membrane and the exchange of monomers and dimers. These results also provide a strong rationale for dynamic studies of GPI-anchored molecules in live cells at steady state and in the absence of cross-linker/clustering agents.
49
Bryan, Tracy M., Karen J. Goodrich, and Thomas R. Cech. "TetrahymenaTelomerase Is Active as a Monomer." Molecular Biology of the Cell 14, no. 12 (December 2003): 4794–804. http://dx.doi.org/10.1091/mbc.e03-07-0474.
Full textAbstract:
Telomerase is an enzyme that utilizes an internal RNA molecule as a template for the extension of chromosomal DNA ends. The catalytic core of telomerase consists of the RNA subunit and a protein reverse transcriptase subunit, known as telomerase reverse transcriptase (TERT). It has previously been shown that both yeast and human telomerase can form dimers or multimers in which one RNA in the complex can influence the activity of another. To test the proposal that dimerization might be essential for telomerase activity, we sought to determine whether Tetrahymena thermophila telomerase is active as a dimer or a monomer. Recombinant Tetrahymena telomerase eluted from a gel filtration column at the size of a monomeric complex (one RNA plus one TERT), and those fractions showed processive telomerase activity. We were unable to detect dimerization of Tetrahymena telomerase by coprecipitation experiments, by using tags on either the TERT protein or telomerase RNA. Therefore, a majority, if not all, of the recombinant Tetrahymena telomerase in our reconstitution system is present as a monomeric complex. We were also unable to detect dimerization of native telomerase from mating and vegetative Tetrahymena cell extracts. These results demonstrate that Tetrahymena telomerase does not need to dimerize to be active and processive.
50
Alhussain Alzuhairi, Mohammed A. "Nano MgO catalyst for chemical depolymerization of polyethylene terephthalate (PET)." Iraqi Journal of Physics (IJP) 16, no. 36 (October 1, 2018): 85–93. http://dx.doi.org/10.30723/ijp.v16i36.33.
Full textAbstract:
This paper focuses firstly on the production of monomers bis (2-hydroxyethyl) terephthalate (BHET) and oligomers by using two different form of MgO light active and Nano Magnesium oxide with different weight ratio (0.15, 0.25 and 0.5) by using chemical recycling glass condenser at 190 ˚C. The second purpose is to study the effect of catalyst ratio, time of reaction and yield of products of the product. Elemental analysis for Carbon –Hydrogen and Nitrogen (CHN), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) have been investigated. Results indicated the catalytic activity was found to correlate with surface area; however, LA MgO has shown an exceptional activity, still it is higher than Nano MgO in order to reduce the reaction time till 30 minutes instead of 7 hours without catalyst. The analysis of the thermograms has indicated the presence of various kinds of monomer, dimer and oligomers that are formed during the recycling; this is particularly evident due to new peaks indicating the formation of BHET monomer and oligomer of lower molecular masses.