Multifunctionality of liver alcohol dehydrogenase.

Liver alcohol dehydrogenase is shown to catalyze dehydrogenation, dismutation and esterolysis. These multifunctional activities were found to associate with all isozymes. The reversible dehydrogenation of alcohols takes place via a random mechanism with a pathway for the formation of enzyme-NADH-alcohol complex which is simplified to an ordered BiBi mechanism at low alcohol concentrations. The same mechanism was followed by the irreversible dismutation of aldehydes except that the contribution of the dead-end enzyme-NADH-aldehyde complex becomes important at low temperatures. The esterolysis does not require nicotinamide coenzyme and proceeds via a Uni Bi mechanism. Both Zn2+ and sulfhydryl group are required for the multifunctional activities. However, their binding/catalytic domains may be nonequivalent albeit overlapping. This is deduced from the following observations: (a) chain length specificities for homologous substrates, (b) cross effects of analogous substrates or products and (c) different responses to various chemical modifications.