Structural Analyses of Mutant and Wild-Type Alcohol Dehydrogenases from Drosophila melanogaster

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Abstract
Four genetic variants of alcohol dehydrogenase from Drosophila melanogaster have been examined: wild-type F-enzyme (from the AdhF strain), the D-type mutant form (from the AdhD strain), which is catalytically active, and two proteins lacking enzymic activity (from the Adhn11 and Adhn5 strains). The proteins were compared by mapping of tryptic peptides. One pair of difference peptides was seen in the comparisons of the D and F-type enzymes. These peptides were purified and their sequences determined. The difference between the two proteins was shown to be an exchange at a single position of glycine in the F for glutamic acid in the D-type protein. This exchange is consistent with the greater acidity of alcohol dehydrogenase from the AdhD strain and can be produced by a single base mutation. The difference between the n11 and F-type proteins was not detected and is suggested to be in a large tryptic peptide. In addition to the difference peptides, other fragments from Drosophila alcohol dehydrogenase were isolated and analyzed. The sequences determined account for approximately 50% of the amino acids in the protein and include regions around the two cysteine residues as well as possible terminal structures. All peptides analyzed were examined for structural identities with horse and yeast alcohol dehydrogenases. No clearly significant similarities were seen between the Drosophila enzyme and the other two proteins but low degrees of homology are possible. From the variations in cysteine-containing regions large differences appear to exist between the active sites of the insect enzyme and the other alcohol dehydrogenases.

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