Biosynthesis of the dimethylbenzene moiety of riboflavin and dimethylbenzimidazole: evidence for the involvement of C-1 of a pentose as a precursor.
The relative incorporations of specially labeled pyruvate, lactate, erythritol, D-erythrose, D-ribose, and D-glucose precursors into the dimethylbenzene carbon atoms of the 5,6-dimethylbenzimidazole unit of vitamin B12 by Propionibacterium shermanii have been determined. The incorporation data provide information regarding the putative four-carbon biosynthetic unit which is involved in the formation of 6,7-dimethyl-8-ribityllumazine and which is the source of the eight dimethylbenzene carbon atoms of both 5,6-dimethylbenzimidazole and riboflavin. The relative incorporations of the labeled lactate and pyruvate precursors are not consistent with either acetoin or 2,3-butanedione functioning as the four-carbon biosynthetic unit. The relative incorporations of the labeled hexose, pentose, and tetrose precursors indicate that the observed incorporation of C-1 of the pentose into the dimethylbenzene carbon atoms does not involve metabolism to a tetrose intermediate, but occurs more directly. It is concluded that the C-1 position of a pentose precursor is involved in the formation of the putative four-carbon biosynthetic unit.[1]References
- Biosynthesis of the dimethylbenzene moiety of riboflavin and dimethylbenzimidazole: evidence for the involvement of C-1 of a pentose as a precursor. Alworth, W.L., Dove, M.F., Baker, H.N. Biochemistry (1977) [Pubmed]
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