Dual function of the alcohol dehydrogenase of Drosophila melanogaster: ethanol and acetaldehyde oxidation by two allozymes ADH-71k and ADH-F.

Until recently the alcohol dehydrogenase of Drosophila melanogaster was thought to act only in the first step of primary alcohol oxidation, producing an aldehyde. Instead, acetic acid is the main product of a two-step process. A rapid procedure was developed for the isolation and purification of two allozymes. The thermostability of the purified enzymes was found to be very different, t 1/2 at 35 degrees C, being 45 min and 130 min for ADH-F and ADH-71k respectively. The kinetic parameters of ethanol oxidation by the two purified allozymes were determined within physiological substrate and coenzyme ranges. The use of artificial electron acceptors has a notable influence on the ethanol oxidation: the apparent Michaelis constants increase; the oxidation rate with ADH-71k increases, whereas it decreases with ADH-F. Purified ADH is shown to be able to catalyze the oxidation of acetaldehyde solely in the presence of NAD+, and PMS and MTT as artificial electron acceptors. From the kinetic data the relative in vivo oxidation rates of ethanol by both ADH allozymes were calculated. ADH-F turned out to be somewhat less effective (30%-40%) than ADH-71k. The physiological consequences of these differences are discussed.