MULTIFUNCTIONAL ACTIVITIES OF PICKEREL LIVER ALCOHOL-DEHYDROGENASE

A major isozyme of pickerel liver alcohol dehydrogenase has been purif ied to homogeneity. The enzyme, in addition to catalyze NAD(P)(+)-link ed dehydrogenation of alcohols, also mediates dismutation of aldehydes and hydrolysis of esters. Steady-state kinetic studies and chemical m odifications of the pickerel liver enzyme with respect to its esteroly tic and dismutative activities were carried out. Pickerel liver alcoho l dehydrogenase catalyzes hydrolyses of p-nitrophenyl esters via a Uni -Bi mechanism, with alkanoic acids as the last product released. Modif ications of Cys and Lys suppress the esterolytic activity. A random me chansim with the formation of dead-end complexes is implicated for the dismutation of octanal catalyzed by pickerel liver alcohol dehydrogen ase. Two amino acid residues, Cys and His, are involved in the dehydro genation as well as dismutation reactions. The present study identifie s a regulatory function of Lys for the multifunctional activities of l iver alcohol dehydrogenase. When the Lys residue is specifically gluco sylated, the dehydrogenase activity increases. Its esterase activity d ecreases, while the dismutase activity remains unchanged.