Brain Aldehyde Dehydrogenase: LOCALIZATION, PURIFICATION, AND PROPERTIES

Abstract

Abstract Aldehyde-oxidizing capacity has been measured in rat, monkey, and bovine brain with the use of indole-3-acetaldehyde and nicotinamide adenine dinucleotide as substrates. The enzyme activity was found to be uniformly distributed in various areas of bovine brain. Mitochondria, prepared by differential and density gradient centrifugation of rat brain homogenates, contained a major portion of the total aldehyde-oxidizing activity while smaller amounts were present in the supernatant fraction. The enzyme was purified from fresh bovine brain and also from frozen and thawed bovine and monkey brains. It has been separated from succinic semialdehyde dehydrogenase. The apparent pH optimum is 10, above which irreversible denaturation occurs. A number of aliphatic aldehydes ranging from formaldehyde to palmitic aldehyde and aldehydes derived from serotonin, epinephrine, and dopamine (3,4-dihydroxyphenylethylamine) were substrates for the enzyme. The rates of oxidation could be correlated with the electropositive nature of the carbonyl carbon atom. The Km values were exceptionally low and ranged from 2 x 10-7 M to 7 x 10-5 M. The enzyme was specific for NAD and NAD analogues. No activity was observed with NADP. The effect of several sulfhydryl-characterizing reagents on the monkey brain enzyme was determined. Tetraethylthiuram disulfide and p-chloromercuribenzoate produced 50% inhibition at approximately 5 x 10-5 M while the enzyme was much less sensitive to γ-(p-arsenosophenyl)-n-butyrate. This study provides direct evidence for the oxidation of aldehydes arising from biologically active amines in the brain. Brain aldehyde dehydrogenase may also be important in oxidizing toxic aldehydes derived from exogenous sources, e.g. acetaldehyde from ethanol.