A comparison of retinene reductase and alcohol dehydrogenase of rat liver.

Retinene reductase, an enzyme which catalyzes the diphosphopyridine nucleotide-dependent reduction of vitamin A aldehyde (retinene) to vitamin A alcohol, was first demonstrated with homogenates of frog and cattle retinas (1, 2). Because crude rabbit liver extracts (3) and crystalline horse liver alcohol dehydrogenase (4) catalyze the oxidation of vitamin A into retinene, the general involvement of alcohol dehydrogenase in this interconversion was suggested (3,4). However, little direct evidence supports this suggestion. Whereas horse liver alcohol dehydrogenase acts on many alcohols (5, B), yeast alcohol dehydrogenase does not oxidize vitamin A (4). In addition, neither retinene reductase nor alcohol dehydrogenase has been purified from tissues of the rat, the species most used for nutritional studies on vitamin A. In view of the oxidation of vitamin A to retinene in the retina, and of the possible role of retinene as a product of p-carotene cleavage in the intestine (7), a detailed study of retinene reduction in the rat was undertaken. The present paper deals with the uptake of intracardially administered radioactive retinene by tissues of the rat, the development of a reliable assay system for retinene reduction, the preparation of a stable retinene reductase from rat liver, and a comparison of acetaldehyde and retinene reduction by this enzyme preparation under a variety of conditions. The same enzyme of rat liver seemingly acts on both substrates, but its activity on retinene and acetaldehyde is affected differently by salts and detergents.