Biosynthesis of type-III porphyrins: nature of the rearrangement process

Abstract
During the biosynthesis of the macrocycle of natural porphyrins (type-III isomer), the porphobilinogen (PBG) unit forming ring D, and no other PBG unit, is found to undergo intramolecular rearrangement; 13C-n.m.r. measurements using double labelled [2,11-13C2] PBG were used.