ビタミンB_<12>補酵素のコバルト : 炭素結合活性化の機構

概要

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Homolytic cleavage of the cobalt-carbon (Co-C) bond of adenosylcobalamin (AdoB_<12>) is an essential early event in the AdoB_<12>-dependent enzymatic reactions. We have investigated the mechanism of activation of the Co-C bond of the coenzyme upon binding to apoprotein of diol dehydrase. All the interactions of the coenzyme with the apoprotein at the adenosyl group, at the peripheral amide side chains of the corrin ring and at the nucleotide loop were found to be essential for activation of the Co-C bond and therefore for catalysis. The presence of the adenosyl group-binding site in the apoenzyme was demonstrated. The specific tight interaction of the adenine moiety of the coenzyme with this site seems to be one element of the force that weakens the Co-C bond. In addition, basal labilization of the Co-C bond through steric distortion of the corrin ring was strongly suggested which may be induced by specific interactions of the propionamide side chains with the apoprotein and by coordination of the bulky base, 5,6-dimethylbenzimidazole, to the cobalt atom. It was also shown that the two ribose moieties in the adenosyl group and in the nucleotide loop play quite different roles in manifestation of function of the coenzyme.
日本ビタミン学会の論文
1988-12-25