BIOSYNTHESIS OF VITAMIN-B12 IN ANAEROBIC-BACTERIA TRANSFORMATION OF 5-HYDROXYBENZIMIDAZOLE AND 5-HYDROXY-6-METHYLBENZIMIDAZOLE INTO 5,6-DIMETHYLBENZIMIDAZOLE IN EUBACTERIUM-LIMOSUM
P. Renz et al., BIOSYNTHESIS OF VITAMIN-B12 IN ANAEROBIC-BACTERIA TRANSFORMATION OF 5-HYDROXYBENZIMIDAZOLE AND 5-HYDROXY-6-METHYLBENZIMIDAZOLE INTO 5,6-DIMETHYLBENZIMIDAZOLE IN EUBACTERIUM-LIMOSUM, European journal of biochemistry, 217(3), 1993, pp. 1117-1121
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.