ENZYME CATALYSIS OF ELECTRON AND GROUP TRANSFER

本基金资助研究的长远目标是

The long term objectives of the research supported by this grant are to determine the chemical mechanisms by which the co-enzyme forms of vitamin B6 (pyridoxal-5'-phosphate, PLP), vitamin B12 (adenosylcobalamin) S-adenosylmethionine (SAM), and [FE-S] clusters function in reactions that cannot be explained by the convention mechanisms established for them. The standard mechanism for the action of PLP entails stabilization of carbanionic intermediates. A major focus of the research supported by this grant is the elucidation of the role of PLP in facilitating isomerizations of substrate radical intermediates, a newly discovered mechanistic role for vitamin B6. PLP- facilitated radical rearrangements appear to take place in aminomutase reactions catalyzed by lysine 2,3-aminomutase, arginine 2,3-aminomutase, D-lysine 5,6-aminomutase and ornithine aminomutase. In the reactions of L-lysine 2,3-aminomutase and D-lysine 5,6-aminomutase, radical intermediates derived from the substrates will be characterized spectroscopically. The roles of SAM and [Fe-S] clusters in the initiation of radical formation will be unmasked and characterized chemically, spectroscopically, and kinetically. 5'-Deoxyadenosyl radical formation from either SAM or adenosylcobalamin appear to initiate the radical rearrangements in the two aminomutases, and this process will be characterized. The relationship between the actin of adenosylcobalamin in vitamin B12-dependent aminomutases on one hand and SAM/[Fe-S] cluster dependent 2,3-aminomutase on the other hand will be elucidated. An important aspect of this research is the elucidation of novel chemistry in the actions of vitamins B6 and B12, SAM, and iron- sulfur centers. Aminomutases play important roles in the biosynthesis of antibiotics. Catalyze steps in amino acid metabolism and the biosynthesis of antibiotics such as Streptothricin F, Mycomycin, Blasticidin S, and Taxol. The contributions of beta-amino acids to the functions of antibiotics are not known. Beta-amino acids appear as O-beta aminoacyl substituents, and as such they contribute positive charges to antibiotic molecules. It is possible that the positive charges ensure solubility and facilitate the delivery of antibiotic to their sites of action, while the O-beta-aminoacyl groups may be biologically stable. If the beta-aminoacyl substituents function in this way, they could become significant in drug delivery strategies, especially for candidate drugs that are minimally soluble.