ALDEHYDE DEHYDROGENASE-ACTIVITY OF DROSOPHILA-MELANOGASTER ALCOHOL-DEHYDROGENASE - BURST KINETICS AT HIGH PH AND ALDEHYDE DISMUTASE ACTIVITY AT PHYSIOLOGICAL PH

The ability of Drosophila alcohol dehydrogenase (D-ADH) to catalyze th e oxidation of aldehydes to carboxylic acids has been re-examined. Pri or studies are shown to have been compromised by a nonenzymic reaction between the aldehydic substrates and amine-containing buffers, e.g., glycine or Tris, and an amine-catalyzed addition of aldehyde to NAD(+) . These reactions interfere with spectrophotometric assays for monitor ing aldehyde oxidation and obscure the nature and scope of D-ADH-catal yzed aldehyde oxidation, particularly at physiological pH. Use of nonr eactive buffers, such as pyrophosphate or phosphate, and H-1 NMR spect roscopy to monitor all the components of the reaction mixture reveals the facile dismutation of aldehydes into equimolar quantities of the c orresponding acids and alcohols at both neutral and high pH. At high p H, dismutation is accompanied by a small burst of NADH production to a steady-state concentration (<10 mu M) that represents a partitioning between NADH dissociation and aldehyde reduction. The increase in A(34 0) is therefore not a direct measure of the aldehyde oxidation reactio n, and the resulting kinetic values cannot be compared to those for al cohol dehydrogenation. The present results for D-ADH, combined with da ta from the literature, establish that aldehyde oxidation, manifest as dismutation, is a widespread property of alcohol dehydrogenases with potential physiological importance in alcohol metabolism and aldehyde detoxification.