BIOSYNTHESIS OF VITAMIN-B12 IN ANAEROBIC-BACTERIA TRANSFORMATION OF 5-HYDROXYBENZIMIDAZOLE AND 5-HYDROXY-6-METHYLBENZIMIDAZOLE INTO 5,6-DIMETHYLBENZIMIDAZOLE IN EUBACTERIUM-LIMOSUM

Eubacterium limosum transformed [2-C-13]5-hydroxybenzimidazole not onl y into [2-C-13]5-hydroxybenzimidazolylcobamide, but also into [2-C-13] 5-methoxy-6-methylbenzimidazolylcobamide and into [2-C-13]5,6-dimethyl benzimidazolylcobamide (vitamin B12). [2-C-13]5-Hydroxy-6-methylbenzim idazole was used by this bacterium to form [2-C-13]5-hydroxy-6-methylb enzimidazolylcobamide, [2-C-13]5-methoxy-6-methylbenzimidazolylcobamid e and [2-C-13]5,6-dimethylbenzimidazolylcobamide. The H-1-NMR spectrum of the 5,6-dimethylbenzimidazole isolated from the C-13-labeled vitam in B12 preparations revealed that the externally added bases had been transformed into the vitamin B12 base almost without dilution of the l abel. This suggests that 5-hydroxybenzimidazole and 5-hydroxy-6-methyl benzimidazole are precursors of 5,6-dimethylbenzimidazole. On the basi s of these results, a hypothetical scheme for the biosynthesis of 5,6- dimethylbenzimidazole via 5-hydroxybenzimidazole and 5-hydroxy-6-methy lbenzimidazole is discussed. This scheme can also explain the formatio n of the other benzimidazole bases found in natural vitamin B12 analog s.