期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 128, 期 4, 页码 1287-1292出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja056333j
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资金
- FIC NIH HHS [5R03TW001212] Funding Source: Medline
- NIDDK NIH HHS [DK45776] Funding Source: Medline
ONIOM calculations have provided novel insights into the mechanism of homolytic Co-C5' bond cleavage in the 5'-deoxyadenosylcobalamin cofactor catalyzed by methylmalonyl-CoA mutase. We have shown that it is a stepwise process in which conformational changes in the 5'-deoxyadenosine moiety precede the actual homolysis step. In the transition state structure for homolysis, the Co-C5'bond elongates by similar to 0.5 angstrom from the value found in the substrate-bound reactant complex. The overall barrier to homolysis is similar to 10 kcal/mol, and the radical products are similar to 2.5 kcal/mol less stable than the initial ternary complex of enzyme, substrate, and cofactor. The movement of the deoxyadenosine moiety during the homolysis step positions the resulting 5'-deoxyadenosyl radical for the subsequent hydrogen atom transfer from the substrate, m ethylmalonyl-CoA.
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