Alcohol dehydrogenase from the fruitfly Drosophila melanogaster Substrate specificity of the alleloenzymes Adh S and Adh UF

Abstract

The substrate specificity of the two alleloenzymes Adh S and Adh UF from Drosophila melanogaster has been studied and found to be similar. With most of the secondary alcohols, the V m 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 Adh UF dissociates at a faster rate than the corresponding complex with Adhs s. For primary alcohols the V m 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.