BIOSYNTHESIS OF PORPHYRINS AND RELATED MACROCYCLES .42. PULSE LABELING EXPERIMENTS CONCERNING THE TIMING OF COBALT INSERTION DURING VITAMIN-B-12 BIOSYNTHESIS

Pulse labelling experiments using Co-60(2+) and [methyl-C-13,C-14]-S-a denosyl-L-methionine have established that in the anaerobic organism P ropionibacterium shermanii cobalt is inserted into the macrocycle afte r the second and before the fourth C-methylation step.