STUDIES ON THE PROPERTIES OF RETINAL ALCOHOL DEHYDROGENASE FROM THE RAT

Abstract— An NAD‐dependent alcohol dehydrogenase (alcohol:NAD oxidoreductase; EC 1.1.1.1) has been isolated and partially purified from the retinal cytosol of the rat. Its substrate specificity and sensitivity to inhibitors of hepatic alcohol dehydrogenase have been investigated. Ethanol, 1‐propanol and 1‐butanol served as substrates for this enzyme but the K m values were more than 100‐fold higher than those reported for hepatic alcohol dehydrogenase. Methanol and retinol were unreactive with this alcohol dehydrogenase. Inhibition by pyrazole was observed but the K t was about 100‐fold higher than the value observed for hepatic alcohol dehydrogenase. n ‐Butyraldoxime inhibited retinal alcohol dehydrogenase with a K t of 2 μM, a value which approximates its K t for hepatic alcohol dehydrogenase. 1, 10‐Phenanthroline was ineffective as an inhibitor. Oxidation of retinol was observed in retinal homogenates in the presence of NADP but no inhibition was observed with ethanol, methanol or pyrazole. We conclude that oxidation of retinol is not catalysed by soluble retinal alcohol dehydrogenase.