MECHANISTICALLY CRYPTIC ENZYME REACTIONS

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The study of two mechanistically cryptic enzyme-catalyzed processes is proposed as are syntheses of a variety of useful, chirally-labeled compounds. An enzyme system from Clostridium aminobutyricum dehydrates 4-hydroxybutanoyl-CoA to E-2-butenoyl-CoA. This process appears to involve the removal of a relatively nonacidic proton and is therefore mechanistically unusual. Proposed studies include determining the overall reaction stereochemistry, evaluating characteristics of an enzyme-catalyzed allylic rearrangement that may be involved, and observing the fates of fluorine-substituted substrates. Substrates and substrate analogs, substituted with deuterium and/or fluorine will be synthesized. 2H and 19F NMR spectroscopy will be used for analyses. Elucidation of the mechanism 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. Enzyme-level characterization of the oxidation of cyclohexanone to adipic acid by the anaerobe Paracoccus sp. NCIB 11086 is also proposed. Reasonable but unprecedented mechanisms will be evaluated, using substrates labeled with 13C and 2H; analyses will be by mass spectrometry. Elucidation of a unique mechanism may facilitate targeting of drugs to anaerobic pathogens. Applications of chirally-labeled oxirane to the synthesis of a variety of useful, labeled biomolecules are proposed.