Multifunctionality of liver alcohol dehydrogenase: Kinetic and mechanistic studies of esterase reaction

Alcohol dehydrogenase from horse liver is shown to catalyze ester hydrolysis. Nicotinamide coenzymes do not affect the rate of esterolysis. A kinetic approach to study esterase reaction at low substrate to enzyme ratio is described. Kinetic effects of ester structure, temperature, pH, solvent polarity, and ionic strength were investigated. The liver enzyme enhances the rate of esterolysis by lowering activation energy of reaction according to the Uni-Bi kinetic sequence. Two ionizable groups, cysteine and lysine, are tentatively assigned at the esterolytic site of liver alcohol dehydrogenase from pH-rate profiles and chemical modification studies. A plausible mechanism for the esterase reaction proceeds via the acid-assisted nucleophilic catalysis involving the ammonium ion of lysine and the thiolate of cysteine in the acyl-oxygen cleavage.