ビタミンB_<12>および関連化合物の化学的研究 : (XXX) 10-Halogeno-dimethylbenzimidazolylcobamide coenzymeのPropanediol dehydratase系における補酵素活性

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Two analogs of 5'-deoxyadenosylcobalamin (DBCC), 10-Cl-DBCC and 10-Br-DBCC, in which the hydrogen atom at 10C position on the corrin ring is replaced by the halogen atom, were prepared by the chemical method using 5'-iodoadenosine or enzymatic method using crude enzyme from Propionibacterium shermanii from their corresponding aquo-forms. In propanediol dehydratase system (EC. 4. 2. 1. 28), the K_m values of the analogs were almost identical with that of DBCC but the V_<max> values of the reactions catalyzed by the analog-apoprotein complex were significantly smaller than that of the normal reaction : DBCC 100,10-Cl-DBCC 40,10-Br-DBCC 20. The decomposition rates of the cobalt-carbon bonds by oxygen in the absence of the substrate were in good agreement with the order of the V_<max> values mentioned above. These facts would indicate that the incorporation of the halogen atoms into the corrin ring influences the nature of the cobalt-carbon bond in such a way that the dissociation of the bond for the exhibition of the coenzyme action is rendered unfavorable.
日本ビタミン学会の論文
1970-01-31

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