Substrate Specificity and Kinetic Properties of NADP+—Dependent Alcohol Dehydrogenase of Phycomyces Blakesleeanus

NADP+-dependent alcohol dehydrogenase (alcohol: NADP+: oxidoreductase, EC 1.1.1.2) was isolated from cell-free extracts of Phycomyces blakesleeanus, and the substrate specificity and kinetic properties of the enzyme were studied. Only primary alcohols were oxidized and of the aldehydes tested, only methanal (formaldehyde) was utilized as a substrate. The enzyme was inactive with NAD+ and was inhibited by pyrazole and by p-chloromercuribenzoate. The apparent Km values at pH 8.3 decreased with increasing chain length of the alcohol substrate. Ethanol had the highest value (1.98x 10M) while the value for 1-heptanol was 2.46 X 10-6M. The maximum velocities (Vmax) decreased as the chain length of the alcohols was increased. The Km value for NADP+ was 1.3 X 10-AIM.