Parallels and Decisive Differences in Vitamin B12 Biosyntheses

Single reactions that are, in principle, similar to those in the cobalt-free biosynthesis of hydrogenbyrinic acid (1) in the aerobe P. denitrificans, but with cobalt-coordinated substrates, occur in the biosynthesis of cobyrinic acid (2) in the anaerobe P. shermanii. This information was obtained from incorporation experiments with 3H/14C doubly labeled precursors from the biosynthetic pathway of P. denitrificans. Previously it had been established that in P. shermanii and the biosynthesis of 2, the cobalt ion is incorporated much earlier than in P. denitrificans.