Heterogeneity of alcohol dehydrogenase enzymes in various tissues

Abstract

The total aldehyde reducing capacity of various tissues, including liver, lung, brain, heart and testes, was determined with propionaldehyde or m-nitrobenzaldehyde as substrate. With each of these substrates, measurements of aldehyde reducing capacity were conducted with NADPH as well as NADH as the cofactors in the absence or presence of pyrazole. The capacity of heart, lung, brain and testes tissues to reduce m-nitrobenzaldehyde was 2- to 10-fold greater than the capacity to reduce propionaldehyde with either NADH or NADPH. However, aldehyde reductase activity in liver tissue was greater with propionaldehyde than with m-nitrobenzaldehyde as substrate. Propionaldehyde reducing capacity of various tissues was inhibited by pyrazole 98–100 per cent with NADH as cofactor, and 25–60 per cent with NADPH as cofactor, depending upon the tissue examined. On the other hand, pyrazole inhibited m-nitrobenzaldehyde reduction only 12–70 per cent with NADH as cofactor, and little inhibition was observed with NADPH as co-substrate. Separation and isolation of two aldehyde reductase fractions from rat liver, which were distinct from alcohol: NAD oxidoreductase (EC 1.1.1.1), was achieved. These fractions differed in substrate and cofactor specificities and in their sensitivity to inhibition by pyrazole and pentobarbital. Similar separations of aldehyde reducing activities were performed with bovine brain tissues, and two distinct enzyme fractions were isolated and compared with the fractions isolated from liver.