Purification and Characterization of a Reduced Nicotinamide Adenine Dinucleotide Phosphate-linked Aldehyde Reductase from Brain*

The presence of a nonspecific NADPH-linked aldehyde reductase (alcohol: NADP oxidoreductase, EC 1.1.1.2) was observed in various areas of bovine brain in vitro. In the midbrain, hypothalamus, and pons, the rate of NADPH oxidation, with p-nitrobenzaldehyde as substrate, was approximately 4.0 nmoles per min per mg of protein; but somewhat lower values were obtained when other regions of the brain were studied. It was found that the enzyme was localized primarily in the soluble supernatant fraction of rat brain homogenates. The enzyme from bovine brain was purified approximately 120-fold and was found to catalyze the reduction of a number of aldehydes, including substituted benzaldehydes, substituted phenylacetaldehydes, and some long chain aliphatic aldehydes. Short chain aliphatic aldehydes such as acetaldehyde or propionaldehyde were not reduced by the enzyme. With p-nitrobenzaldehyde as substrate, NADPH, but not NADH, was oxidized by bovine brain aldehyde reductase. The pH optimum for the enzyme was found to be 6.75 for aldehyde reduction, whereas the rate of oxidation of p-hydroxyphenylethanol, with NADP as cosubstrate, was optimal at pH 9.7. K, values for various substrates ranged from 3.7 X 1OV M to 1.4 X 1O-4 M. K, values for various substituted benzaldehydes were correlated with the electropositive nature of the carbonyl carbon atom by the Hammet a-p relationship. Oxidation of NADPH by the partially purified enzyme was inhibited approximately 50% by 0.1 mM concentrations of amytal, phenobarbital, or chlorpromazine. The enzyme activity was not altered, however, by 10 mM pyrazole.