STEREOCHEMISTRY AND MECHANISMS OF ENZYME REACTION

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The study of two mechanistically cryptic enzyme-catalyzed dehydration reactions is proposed. An enzyme system from Clostridium aminobutyricum dehydrates 4-hydroxy butyryl CoA to E-2-butenoyl CoA, and another enzyme system, from Megasphera elsdenii, converts L-lactyl CoA to acrylyl CoA. These processes appear to involve the removal of relatively nonacidic protons, in contrast to the vast majority of enzyme-catalyzed dehydration reactions, in which the hydroxyl group and the proton which are eliminated are situated alpha- and beta-, respectively, to a carbanion-stabilizing functional group (esp. a carbonyl). These reactions will be studied by determining overall reaction stereochemistry, by observing the fates of fluorine-substituted substrates, by determining isotope effects, and by looking for partial exchanges involving protons and hydroxyl groups. These studies will require the synthesis of chirally labeled ethylene oxide, a potentially useful and hitherto unknown synthon. Elucidation of the mechanisms of these two dehydrations will help to define the structural and mechanistic requirements of enzyme-catalyzed dehydrations in general. Such information can be of great utility in predicting pathways of secondary metabolism as well as metabolism of foreign substances, including toxins and drugs.