Methylglyoxal as substrate and inhibitor of human aldehyde dehydrogenase: Comparison of kinetic properties among the three isozymes

Abstract

Methylglyoxal was demonstrated to be a substrate for the isozymes E1, E2 and E3 of human aldehyde dehydrogenase. Pyruvate was the product from the oxidation of methylglyoxal by the three isozymes. At pH 7.4 and 25 oC, the major and minor components of the E3 isozyme catalyzed the reaction with V max of 1.1 and 0.8 μmol NADH min −1 mg −1 protein, respectively, compared to 0.067 and 0.060 μmol NADH min −1 mg −1 protein for the E1 and E2 isozymes, respectively. The E2 isozyme had a K m for methylglyoxal of 8.6 μM, the lowest compared to 46 μM for E1 and 586 and 552 μM for the major and minor components of the E3 isozyme, respectively. Both components of the E3 isozyme showed substrate inhibition by methylglyoxal, with K i values of 2.0 mM for the major component and 12 mM for the minor component at pH 9.0. Substrate inhibition by methylglyoxal was not observed with the E1 and E2 isozymes. Methylglyoxal strongly inhibited the glycolaldehyde activity of the E1 and E2 isozymes. Mixed-type models of inhibition were employed as an approach to calculate the inhibition constants, 44 and 10.6 μM for E1 and E2 isozymes, respectively.