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.

Biosynthesis of riboflavin in Bacillus subtilis: origin of the four-carbon moiety

“…2 and 3). This result is comparable to the incorporation of [1-'3C]ribose into positions 6 and 8ot of riboflavin, which had been observed in earlier experiments with the fungus A. gossypii (3,4). It follows that symmetrical compounds such as diacetyl can be ruled out as precursors.…”

Precursor of carbon atom five and hydroxymethyl carbon atom of the pyrimidine moiety of thiamin in Escherichia coli.

“…The ribose moiety of GTP has been found to participate in the constitution of vitamins such as folic acid (11) and riboflavin (12). It has been considered that the pyrimidine is synthesized from AIR, but the ribose phosphate is liberated from the imidazole ring and does not participate in the formation of the pyrimidine from AIR (1, 2).…”

Biosynthesis of Riboflavin, Folic Acid, Thiamine, and Pantothenic Acid

“…26 for a critical discussion). The recent comparison by Alworth et al (27) of the incorporation into riboflavin of various labeled substances by Propionibacterium shemanii has supported the view that a pentose is the precursor, and this proposal is further supported by the observation of Bresler et al (28) that a riboflavinrequiring mutant o f B. subtilis accumulates and excretes a compound that they isolated and identified as 6-methyl-7-( 1 ',2'-dihydroxyethyl)-8-ribityllumazine (MERL, shown in Fig. 1 as VI).…”