Abstract
The substrate specificity of the two alleloenzymes AdhS an AdhUF from Drosophila melanogaster has been studied and found to be similar. With most of the secondary alcohols, the Vm value is essentially the same, and indicative of a Theorell-Chance mechanism with rate-limiting enzyme-coenzyme dissociation. The experiments indicate that the enzyme-coenzyme complex formed with AdhUF dissociates at a faster rate than the corresponding complex with AdhS. For primary alcohols the Vm value is much lower than for secondary alcohols, varies with the type of alcohol and the dissociation of the enzyme-coenzyme complex is not rate limiting. For these alcohols a primary isotope effect with deuteroethanol indicates that it is the interconversion of the ternary complexes that is rate determining. Studies with the enantiomers of butan-2-ol and octan-2-ol show that both alkyl groups in the secondary alcohols interact hydrophobically with the alcohol-binding region of the active site. However, the two parts of the alcohol-binding region that interact with the two alkyl groups are of different size. The high activity observed with secondary alcohols and especially with (R)-(+)-cis-verbenol, indicates that these flies can metabolize terpenes. Such compounds may be part of the pheromone system in the flies with D. melanogaster alcohol dehydrogenase playing a role in pheromone metabolism.
