Mouse alcohol dehydrogenase 4: kinetic mechanism, substrate specificity and simulation of effects of ethanol on retinoid metabolism

Mouse ADH4 (purified, recombinant) has a low catalytic efficiency for ethan ol and acetaldehyde, but very high activity with longer chain alcohols and aldehydes, at pH 7.3 and temperature 37 degreesC. The observed turnover num bers and catalytic efficiencies for the oxidation of all-trans-retinol and the reduction of all-trans-retinal and 9-cis-retinal are low relative to ot her substrates; 9-cis-retinal is more reactive than all-trans-retinal. The reduction of all-trans- or 9-cis-retinals coupled to the oxidation of ethan ol by NAD(+) is as efficient as the reduction with NADH. However, the Micha elis constant for ethanol is about 100 mM, which indicates that the activit y would be lower at physiologically relevant concentrations of ethanol, Sim ulations of the oxidation of retinol to retinoic acid with mouse ADH4 and h uman aldehyde dehydrogenase (ALDH1), using rate constants estimated for all steps in the mechanism, suggest that ethanol (50 mM) would modestly decrea se production of retinoic acid. However, if the K-m for ethanol were smalle r, as for human ADH4, the rate of retinol oxidation and formation of retino ic acid would be significantly decreased during metabolism of 50 mM ethanol . These studies begin to describe quantitatively the roles of enzymes invol ved in the metabolism of alcohols and carbonyl compounds. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.