Drosophila melanogaster alcohol dehydrogenase: An electrophoretic study of the AdhS,AdhF, and AdhUF alleloenzymes

The nature and the interconversion of the three multiple forms Adh-5, Adh-4, and Adh-3 of the purified alleloenzymes Adh^S, Adh^F, and Adh^UF from the fruitflyDrosophila melanogaster have been examined. The experiments show that these multiple forms differ from those in crude extracts of flies homozygous at the Adh locus. On electrophoresis in a starch gel containing NAD or NADH, of purified Adh^S which consists of the three Adh forms S-5, S-4, and S-3, five enzymatically active zones appear. This contrasts with the single active zone that arises with crude extracts. Of the five zones that appear with purified enzyme, S-5 gives rise to one, while the other four zones come from the two minor forms S-4 and S-3. The occurrence of the three multiple forms Adh-5, Adh-4, and Adh-3 for each of the purified alleloenzymes is considered due to Adh-5 and, in the case of Adh-4 and Adh-3, deamidation of Adh-5, with the Adh-3 fraction also containing some reversible modified Adh-5. Of the labile amides, at least one must be located in the coenzyme binding region with deamidation preventing coenzyme binding. Pure NAD does not convert Adh-5 to Adh-3 and Adh-1. To produce conversion, the presence of either acetone or butanone along with NAD is necessary. Increased amounts of either acetone or butanone result in increased conversion. In contrast to this, none of the carbonyl compounds cyclohexanone, (+)- and (−)-verbenone, acetaldehyde, acrolein, or crotonaldehyde produces conversion. The ketone group binds to the alcohol binding site in the enzyme-NAD complex. Conversion is considered due to the ketone group binding to a nucleophilic amino acid residue and forming a bridge to the C-4 of the nicotinamide moiety of NAD.