title: Biosynthesis of the dimethylbenzene moiety of riboflavin and dimethylbenzimidazole: evidence for the involvement of C-1 of a pentose as a precursor.
abstract: 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.
mesh_terms: D001562:Benzimidazoles / Q000378:metabolism*; D001665:Binding Sites; D004896:Erythritol / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D011424:Propionibacterium / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D012256:Riboflavin / Q000096:biosynthesis*; D012266:Ribose / Q000378:metabolism; D013780:Tetroses / Q000378:metabolism
chemical_list: D001562:Benzimidazoles; D007773:Lactates; D011773:Pyruvates; D013780:Tetroses; D012266:Ribose; D005947:Glucose; D004896:Erythritol; D012256:Riboflavin