Kinetic analysis of the catalytic properties of peptides in ester hydrolysis

The catalytic properties of peptides containing histidine, cysteine and aspartic acid in ester hydrolysis were studied. Saturation kinetics were found for the reaction of p-nitrophenyl acetate (NPA) with Z-His-Ala-Asp-Gly-Cys-NH2 and Z-His-Ala-Gly-Cly-Cys-NH2. The Brönsted equation for the hydrolysis of tert-butyloxcarbonyl-L-alanine-p-nitrophenylester (Bos-Ala-ONp) catalyzed by simple imidazole and SH-compounds was determined. The catalytic behaviour of the peptides in ester hydrolysis could not be described by the Brönsted equations for imidazole o thiole catalyzed hydrolysis of NPA and Boc-Ala-ONp. The pH dependence of the rate constants of the catalyzed ester hydrolysis gave no linear plots in 1/k versus H+ diagrrams.