The Hydrolysis of Esters Related to O-Hippuryl-2-hydroxybutanoic Acid by Carboxypeptidase A

Abstract

The hydrolysis of each of the following esters by bovine carboxypeptidase A has been studied at pH 7.5, 25°, ionic strength 0.5: O-hippuryl-, O-phenaceturyl-, O-aceturyl-, O-(N-methylhippuryl)-, and O-(N-hippurylglycyl)-2-hydroxybutanoic acids, and 2-(3-benzoylpropanoxy)-, 2-benzoxyacetoxy-, and 2-(4-phenylbutanoxy)butanoic acids. Substrate inhibition occurs with only the hippuric and phenaceturic acid esters and in the six other cases simple Michaelis–Menten kinetics are observed. The relatively minor variations in the structures of the acid moieties of these esters lead to quite large variations in Km, although kcat seems to be relatively independent of the nature of the acid moiety. Binding modes of substrate molecules at both the catalytic and inhibitory sites are discussed in the light of these observations.