title: Kinetics and thermodynamics of ethanol oxidation catalyzed by genetic variants of the alcohol dehydrogenase from Drosophila melanogaster and D. simulans.
abstract: Four naturally occurring variants of the alcohol dehydrogenase enzyme (ADH; EC 1.1.1.1) from Drosophila melanogaster and D. simulans, with different primary structures, have been subjected to kinetic studies of ethanol oxidation at five temperatures. Two amino acid replacements in the N-terminal region which distinguish the ADH of D. simulans from the three ADH allozymes of D. melanogaster generate a significantly different activation enthalpy and entropy, and Gibbs free energy change. The one or two amino acid replacements in the C-terminal region between the ADH allozymes of D. melanogaster do not have such clear-cut effects. All four ADH variants show highly negative activation entropies. Sarcosine oxidation by the ADH-71k variant of D. melanogaster has an activation energy barrier similar to that of ethanol oxidation. Three amino acid differences between the ADH of D. simulans and the ADH-F variant of D. melanogaster influence the kappa cat and kappa cat/Kethm constant by a maximum factor of about 2 and 2.5, respectively, over the whole temperature range. Product inhibition patterns suggest a 'rapid equilibrium random' mechanism of ethanol oxidation by the ADH-71k, and the ADH of D. simulans.
mesh_terms: D000426:Alcohol Dehydrogenase / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D004330:Drosophila / Q000201:enzymology* / Q000235:genetics; D004331:Drosophila melanogaster / Q000201:enzymology / Q000235:genetics; D000431:Ethanol / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D013816:Thermodynamics
chemical_list: D007527:Isoenzymes; D000431:Ethanol; D000426:Alcohol Dehydrogenase