KINETICS OF NATIVE AND CHEMICALLY ACTIVATED HUMAN LIVER ALCOHOL DEHYDROGENASES

Acetimidylation and methylation of alcohol dehydrogenase from human livers of the normal phenotype (B 1 B 1 ) increases activity and Michaelis and inhibition constants, suggesting that an amino group at the active site is modified, as was shown previously for the horse enzyme. The enzyme from atypical phenotype (B 1 B 2 ) was only activated 2-fold by acetimidylation, which may indicate that substitution of Pro for Ala-230 or modification of Lys-228 is sufficient to fully activate the enzyme. Product inhibition patterns for native and modified human enzymes are consistent with an Ordered Bi Bi mechanism. However, the major isoenzyme of native human liver alcohol dehydrogenase B 1 B 1 exhibits nonlinear kinetics over a wide range of ethanol concentrations, indicating the presence of subunits with different kinetic characteristics or negative cooperativity between subunits. Chemical modification makes the kinetics linear and alters the mechanism.