Carboxylesterases (EC 3.1.1). Kinetic studies on carboxylesterases

Abstract

Kinetic evidence has been obtained which is consistent with the formation of an acyl-enzyme intermediate in the hydrolysis of butyrate esters catalyzed by pig liver carboxylesterase. A study of the pig liver carboxylesterase- catalyzed hydrolysis of phenyl butyrate revealed activation by substrate and by modifiers such as benzene. This activation has been interpreted in terms of a classical kinetic scheme involving sites for substrate and modifier on a single enzyme molecule. For a series of activated esters, the catalytic rate constants for the carboxylesterase-catalyzed hydrolyses were found to be relatively insensitive to changes in the acyl group, indicating that binding is not responsible for the high reactivity of these systems. Kinetic and other data suggest that there are possibly some different elements of essential chemistry between the esterases and the proteinases.