ビタミンB_<12>および関連化合物の化学的研究 : (XXIX) ビタミンB_<12>補酵素カルボン酸のPropanediol dehydratase系における補酵素活性

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Analogs of 5'-deoxyadenosylcobalamin (DBCC) having one to three carboxyl groups at position(s) b, d and/or e on the corrin ring (DBCC-(COOH)_<1〜3>) have been prepared by reacting the corresponding cob(I)alamin carboxylic acids with 5'-iodoadenoisine. In propanediol dehydratase system (EC. 4. 2. 1. 28) the analogs with two or three propionic acid side-chains (DBCC-(COOH)_2 or DBCC-(COOH)_3) did not serve as the coenzyme, whereas all of the three isomers of DBCC-(COOH)_1 were effective. Although K_m values for the three isomers were almost identical (9-16 X 10^<-6> M, i.e. 10 to 20 times that for DBCC), significant differences were observed among the V_<max> values of the reactions dependent on these isomers. The V_<max> values were as follows : DBCC-b-(COOH)_1 (analog having propionic acid side-chain at position b), 96%; DBCC-d-(COOH)_1,57%; DBCC-e-(COOH)_1,17%, as compared with that of DBCC. Three isomers of OH-B_<12>-(COOH)_1 acted as the competitive inhibitors for the enzyme used, and their K_i values were almost similar. The cobalt-carbon bonds of the complexes of the three isomers with apoprotein were irreversibly cleaved under aerobic conditions in the absence of the sustrate as is the case of the normal holoenzyme, and the order of their inactivation rates was in accord with the order of the V_<max> values mentioned above. These results would suggest that the three propionamide side-chains have similar influences on the affinity between B_<12> coenzyme and apoprotein of propanediol dehydratase, and, nevertheless, the modification of the position e causes the most significant decrease in the catalytic activity of the resulting holoenzyme species.
日本ビタミン学会の論文
1970-01-31

ビタミンB_<12>および関連化合物の化学的研究 : (XXIX) ビタミンB_<12>補酵素カルボン酸のPropanediol dehydratase系における補酵素活性

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