Kinetic interpretations of active site topologies and residue exchanges in Drosophila alcohol dehydrogenases

1. A comparison of full and partly sequenced Adhs from various Drosophila species reveal that 127 of their 253-255 positions are identical (50% identity). 2. Fifty-six of the 115 C-terminal amino acids building up the alcohol binding region differ. In spite of the large differences in primary structure of the alcohol binding region in the Adh enzyme in distantly related Drosophila species, the substrate specificity and stereospecificity have been retained. The topology of the alcohol binding region has been largely conserved during evolution. 3. The primary structures of the alcohol dehydrogenases (Adh) in the Sophophora subgenus is distinguished by few amino acid exchanges, and kinetic and activity parameters show that those at positions 14, 82, 192 and 214 are directly or indirectly involved in coenzyme binding. 4. In these non-metallo Adhs, a tyrosine has been tentatively identified as a nucleophilic catalyst of the hydride transfer step. The three tyrosines at positions 63, 152 and 178 are conserved among the Drosophila alcohol dehydrogenases.