1. Homogenates of Propionibacterium freudenreichii transform riboflavin into 5,6-dimethylbenzimidazole. This process is stimulated by nicotinamide. Homogenates of Propionibacterium shermanii form only small amounts of 5,6-dimethylbenzimidazole from riboflavin in the absence of nicotinamide, but also form appreciable amounts in the presence of nicotinamide.2. The stimulation of the 5,6-dimethylbenzimidazole-forming system by nicotinamide shows a lag phase which is abolished by preincubation of the homogenate with nicotinamide. Since no lag phase is observed when nicotinamide is replaced by nicotinate, nicotinate seems to be the true stimulating agent. These observations are in agreement with the fact that nicotinamide is rapidly split to nicotinate in homogenates of P. jreudenreichii.3. The 5,6-dimethylbenzimidazole-forming homogenate system is only active at a high buffer concentration (0.3-0.5 M) and in the presence of oxygen. The system has a pronounced oxygen optimum .4. Flavin mononucleotide and flavin-adenine dinucleotide are better substrates for the 5,6-dimethylbenzimidazole-forming homogenate system than riboflavin. But with [l '-14C]riboflavin as substrate the specific radioactivity of 5,6-dimethylbenzimidazole is higher than the specific radioactivity of flavin -adenine dinucleotide and lower than the specific radioactivity of flavin mononucleotide. Therefore flavin mononucleotide is the immediate substrate for the formation of 5,6-dimethylbenzimidazole.5. A tentative reaction sequence for the transformation of flavin mononucleotide into 5,6-dimethylbenzimidazole is discussed.
In order to elucidate the biosynthesis of the base moiety of cobalamin in Salmonella typhimurium LT2, this organism was grown in the presence of [1'-14C]riboflavin. The vitamin B12 isolated was 14C-labeled. It was shown by chemical degradation that the 14C-label was exclusively localized in carbon atom 2 of the 5,6-dimethylbenzimidazole moiety. This demonstrated the precursor function of riboflavin in the biosynthesis of 5,6-dimethylbenzimidazole in S. typhimurium.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.