Order of assembly of the four pyrrole rings during biosynthesis of the natural porphyrins

Abstract

13 C-Labelling experiments involving relatively large quantities of deaminase-cosynthetase show that the four pyrrole rings of uro'gen-III (5), and thus also of the natural porphyrins, are assembled starting from ring A with sequential addition of rings B, C, and finally ring D; ring D is that which undergoes rearrangement.