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One-step Mechanism (one-step + mechanism)
Selected AbstractsPotency and selectivity of inhibition of cathepsin K, L and S by their respective propeptidesFEBS JOURNAL, Issue 20 2000Jocelyne Guay The prodomains of several cysteine proteases of the papain family have been shown to be potent inhibitors of their parent enzymes. An increased interest in cysteine proteases inhibitors has been generated with potential therapeutic targets such as cathepsin K for osteoporosis and cathepsin S for immune modulation. The propeptides of cathepsin S, L and K were expressed as glutathione S -transferase-fusion proteins in Escherichia coli. The proteins were purified on glutathione affinity columns and the glutathione S -transferase was removed by thrombin cleavage. All three propeptides were tested for inhibitor potency and found to be selective within the cathepsin L subfamily (cathepsins K, L and S) compared with cathepsin B or papain. Inhibition of cathepsin K by either procathepsin K, L or S was time-dependent and occurred by an apparent one-step mechanism. The cathepsin K propeptide had a Ki of 3.6,6.3 nm for each of the three cathepsins K, L and S. The cathepsin L propeptide was at least a 240-fold selective inhibitor of cathepsin K (Ki = 0.27 nm) and cathepsin L (Ki = 0.12 nm) compared with cathepsin S (Ki = 65 nm). Interestingly, the cathepsin S propeptide was more selective for inhibition of cathepsin L (Ki = 0.46 nm) than cathepsin S (Ki = 7.6 nm) itself or cathepsin K (Ki = 7.0 nm). This is in sharp contrast to previously published data demonstrating that the cathepsin S propeptide is equipotent for inhibition of human cathepsin S and rat and paramecium cathepsin L [Maubach, G., Schilling, K., Rommerskirch, W., Wenz, I., Schultz, J.E., Weber, E. & Wiederanders, B. (1997), Eur J. Biochem. 250, 745,750]. These results demonstrate that limited selectivity of inhibition can be measured for the procathepsins K, L and S vs. the parent enzymes, but selective inhibition vs. cathepsin B and papain was obtained. [source] Thermal properties of extruded/injection-molded poly(lactic acid) and biobased composites,,JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Abdellatif A. Mohamed Abstract To determine the degree of compatibility between poly(lactic acid) and different biomaterials (fibers), poly(lactic acid) was compounded with sugar beet pulp and apple fibers. The fibers were added in 85 : 15 and 70 : 30 poly(lactic acid)/fiber ratios. The composites were blended by extrusion followed by injection molding. Differential scanning calorimetry and thermogravimetric analysis were used to analyze the extruded and extruded/injection-molded composites. After melting in sealed differential scanning calorimetry pans, the composites were cooled through immersion in liquid nitrogen and aged (stored) at room temperature for 0, 7, 15, and 30 days. After storage, the samples were heated from 25 to 180°C at 10°C/min. The neat poly(lactic acid) showed a glass-transition transition at 59°C with a change in heat capacity (,Cp) value of 0.464. The glass transition was followed by crystallization and melting transitions. The enthalpic relaxation of the poly(lactic acid) and composites steadily increased as a function of the storage time. Although the presence of fibers had little effect on the enthalpic relaxation, injection molding reduced the enthalpic relaxation. The crystallinity percentage of the unprocessed neat poly(lactic acid) dropped by 95% after extrusion and by 80% for the extruded/injection-molded composites. The degradation was performed in air and nitrogen environments. The degradation activation energy of neat poly(lactic acid) exhibited a significant drop in the nitrogen environment, although it increased in air. This meant that the poly(lactic acid) was more resistant to degradation in the presence of oxygen. Overall, injection molding appeared to reduce the activation energy for all the composites. Sugar beet pulp significantly reduced the activation energy in a nitrogen environment. In an air environment, both sugar beet pulp and apple fibers increased the activation energy. The enzymatic degradation of the composites showed a higher degradation rate for the extruded samples versus the extruded/injection-molded composites, whereas the apple composites exhibited higher weight loss. The thermogravimetric analysis data showed that the degradation of unprocessed and extruded neat poly(lactic acid) followed a one-step mechanism, whereas extruded/injection-molded composites showed two-step degradation. A higher fiber content resulted in up to three-step degradation mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Kinetic study of the decomposition of 2-butanol on carbon-based acid catalystAICHE JOURNAL, Issue 6 2010J. Bedia Abstract The catalytic conversion of 2-butanol on a carbon-based acid catalyst prepared by chemical activation of olive stone with phosphoric acid was investigated. The carbon catalyst showed a considerable amount of surface phosphorus, presumably in form of phosphate groups, as revealed by XPS, despite a washing step carried out after the activation process. Conversion of 2-butanol yields mainly dehydration products, mostly cis-2-butene and trans-2-butene with lower amounts of 1-butene, and a very small amount of mek as dehydrogenation product. Kinetic interpretation of the experimental data was performed using two elimination mechanisms for the dehydration reaction; an E1-mechanism (two-step mechanism) and an E2-mechanism (one-step mechanism). The rate expressions derived from both models fit properly the experimental results, suggesting that probably the two mechanisms occur simultaneously. This is supported by the similar rate constant obtained for the formation of the carbocation and the olefins in the E1 and E2 mechanisms, respectively. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Reactivities of acridine compounds in hydride transfer reactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2007In-Sook Han Lee Abstract Reactivities of acridine derivatives (10-benzylacridinium ion, 1a+, 10-methylacridinium ion, 1b+, and 10-methyl-9-phenylacridinium ion, 1c+) have been compared quantitatively for hydride transfer reactions with 1,3-dimethyl-2-substituted phenylbenzimidazoline compounds, 2Ha,h. Reactions were monitored spectrophotometrically in a solvent consisting of four parts of 2-propanol to one part of water by volume at 25,±,0.1,°C. Reduction potentials have been estimated for acridine derivatives by assuming that the equilibrium constants for the reductions of 1a+,c+ by 2Hb would be the same in aqueous solution and accepting ,361,mV as the reduction potential of the 1-benzyl-3-carbamoylpyridinium ion. The resulting reduction potentials, E, are ,47,mV for 1a+, ,79,mV for 1b+, and ,86,mV for 1c+. Each of acridine derivatives gives a linear Brønsted plot for hydride transfer reactions. The experimental slopes were compared with those obtained by Marcus theory. This comparison shows that the kinetic data are consistent with a one-step mechanism involving no high-energy intermediates. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||