α-Chymotrypsin-catalyzed Hydrolysis of Phenyl Acetate

Publisher Website
Google Scholar
Abstract
A detailed examination of the mechanism of the hydrolysis of phenyl acetates by α-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 acetyliniidazole were observed when the acetyl-enzyme was denaturated with sodium dodecyl sulfate. These results indicate the participation of histidine-acylated enzyme, which would account for the anomalous phenomena previously found in this system, including a large value of Hammett's ρ. The relation between the substrate activation and the two intermediates is discussed.