PURIFICATION AND CHARACTERIZATION OF DIMERIC DIHYDRODIOL DEHYDROGENASE FROM DOG LIVER

High NADP(+)-linked dihydrodiol dehydrogenase activity was detected in dog liver cytosol, from which a dimeric enzyme composed of M(r) 39,00 0 subunits was purified to homogeneity. The enzyme oxidized trans-cycl ohexanediol, and trans-dihydrodiols of benzene and naphthalene, the [1 R,2R]-isomers of which were selectively oxidized. In the reverse react ion in the presence of NADPH as a coenzyme, the enzyme reduced alpha-d icarbonyl compounds, such as methylglyoxal, 3-deoxyglucosone, and diac etyl, and some compounds with a carbonyl group, such as glyceraldehyde , lactaldehyde, and acetoin. 4-Hydroxyphenylketones and ascorbates inh ibited the enzyme. The results of steady-state kinetic analyses indica ted that the reaction proceeds through an ordered bi bi mechanism with the coenzyme binding to the free enzyme, and suggested that the inhib itors bind to the enzyme-NADP(+) binary complex. The dimeric enzyme wa s detected in liver and kidney of dog, and was immunochemically simila r to the dimeric enzymes from monkey kidney, rabbit lens, and pig live r. The sequences (total 127 amino acid residues) of eight peptides der ived on enzymatic digestion of the dog liver enzyme did not show signi ficant similarity with the primary structures of members of the aldo-k eto reductase and short chain dehydrogenase superfamilies, which inclu de monomeric dihydrodiol dehydrogenases and carbonyl reductase, respec tively.