Biosynthesis of cobalamin in Salmonella typhimurium: transformation of riboflavin into the 5,6-dimethylbenzimidazole moiety

In order to elucidate the biosynthesis of the base moiety of cobalamin in S almonella typhimurium LT2, this organism was grown in the presence of [1'-C -14]riboflavin. The vitamin B-12 isolated was C-14-labeled. It was shown by chemical degradation that the C-14-label was exclusively localized in carb on atom 2 of the 5,6-dimethylbenzimidazole moiety. This demonstrated the pr ecursor function of riboflavin in the biosynthesis of 5,6-dimethylbenzimida zole in S. typhimurium.