Biosynthesis of vitamin B12: mode of incorporation of factor III into cobyrinic acid

Abstract

Extensive chemical degradation of cobyrinic acid biosynthesized from a sample of factor III radiochemically labeled in its three methyl groups demonstrates that label is retained exclusively in the two methyl groups at positions C-2 and C-7 and confirms that the C-20 methyl group of the precursor is lost during formation of the corrin ring system.