Kinetic study on the acylation step of alpha-chymotrypsin-catalyzed hydrolysis of acylimidazole. A model reaction of specific peptide substrate activated by binding to the enzyme.

摘要: As a model reaction of the enzyme-bound activated peptide substrates in proteinase-catalyzed hydrolysis, alpha-chymotrypsin-catalyzed hydrolysis three acylimidazoles (trans-cinnamoylimidazole, indoleacryloylimidazole, and furylacryloylimidazole) was studied, especially as regards acylation process. The complicated pH-dependences reactions, due mainly to existence protonated forms these acylimidazoles, were analyzed based on scheme considering so-called inactive monomeric enzyme dimeric enzyme. intrinsic parameters for individual species evaluated. through mono-protonated enzyme-substrate complex (ESH) reflects rate attach by Ser-195 O gamma carbonyl carbon acylimidazolium, where formation possible tetrahedral intermediate is rate-determining. via non-protonated (ES) between those esters (as single bond character cleaved linkage) amides (with respect proton transfer key process acylation). This confirmed observation acceleration upon addition external donors. Based results, mechanism substrate discussed.