ALDEHYDE DISMUTASE ACTIVITY OF HUMAN LIVER ALCOHOL-DEHYDROGENASE

Human alcohol dehydrogenases of class I and class II but not class III catalyse NAD(+)-dependent aldehyde oxidation in addition to the NADH- dependent aldehyde reduction, The two reactions are coupled, i,e, the enzymes display dismutase activity, Dismutase activity of recombinantl y expressed human class T isozymes beta(1) beta(1) and gamma(2) gamma( 2), class II and class III alcohol dehydrogenases was assayed with but anal as substrate by gas chromatographic-mass spectrometric quantitati ons of butanol and butyric acid, The class I gamma(2) gamma(2) isozyme showed a pronounced dismutase activity with a high k(cat), 1300 min(- 1), and a moderate K-m, 1.2 mM, The class I beta(1) beta(1) isozyme an d the class LT alcohol dehydrogenase showed moderate catalytic efficie ncies for dismutase activity with lower k(cat) values, 60-75 min(-1). 4-Methylpyrazole, a potent class I ADH inhibitor, inhibited the class I dismutation completely, but cyanamide, an inhibitor of mitochondrial aldehyde dehydrogenase, did not affect the dismutation, The dismutase reaction might be important for metabolism of aldehydes during inhibi tion or lack of mitochondrial aldehyde dehydrogenase activity.