alpha-chymotrypsin-catalyzed hydrolysis of phenyl acetate. Large Hammett's rho constant and participation of histidine-acylated intermediate.
A detailed examination of the mechanism of the hydrolysis of phenyl acetates by alpha-chymotrypsin [EC 3.4.21.1] was carried out. The effective deacylation rate constants of some phenyl acetates obtained by titration of the acetyl-enzyme decreased at low substrate concentrations and showed anomalous pH dependences and solvent isotope effects. The transient kinetics of deacylation of the acetyl-enzyme were biphasic. A spectrum and a breakdown rate similar to those of acetylimidazole were observed when the acetyl-enzyme was denaturated with sodium dodecyl sulfate. These results indicate the participation of histidine-acylated enzyme, which woud account for the anomalous phenomena previously found in this system, including a large value of Hammett's rho. The relation between the substrate activation and the two intermediates is discussed.
D000215:Acylation; D002722:Chlorobenzenes / Q000494:pharmacology; D002733:Chlorophenols / Q000494:pharmacology; D002918:Chymotrypsin / Q000378:metabolism*; D003903:Deuterium; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration; D010648:Phenylacetates / Q000378:metabolism*; D011489:Protein Denaturation; D012967:Sodium Dodecyl Sulfate
D002722:Chlorobenzenes; D002733:Chlorophenols; D010648:Phenylacetates; D012967:Sodium Dodecyl Sulfate; D006639:Histidine; D003903:Deuterium; D002918:Chymotrypsin