aXeto Aldehyde Dehydrogenase, An Enzyme That Catalyzes the Enzymic Oxidation of Methylglyoxal to Pyruvate*

An enzyme which catalyzes the oxidation of methylglyoxal to pyruvic acid was partially purified from aqueous extracts of sheep liver acetone powders. NAD+ or NADP+ was necessary for the oxidation. Changes in methylglyoxal, pyruvate, and pyridine nucleotide were stoichiometrically equivalent. Of various carbonyl-containing compounds tested, only oc-keto aldehydes were substrates. Enzyme activity was found only in the supernatant fraction of liver cells. Evidence is presented that the conversion of methylglyoxal to pyruvate was direct and did not involve its preliminary conversion to lactate. Activity increased up to pH 10.4 with no indication of a pH optimum. K, values for methylglyoxal with respect to NADP’ were smaller than with respect to NADf. The ratio of rates of NAD+ to NADP+ reduction varied with the nature of the substrate and type of inhibitor. The name Lu-keto aldehyde dehydrogenase is suggested. The possible function of this new enzyme activity is discussed in relation to the suggested origins and physiological functions of methylglyoxal.