Chemical and enzymic studies on biosynthesis of the natural porphyrin macrocycle: Formation and role of unrearranged hydroxymethylbilane and order of assembly of the pyrrole rings

Abstract

Following a review of the background to current research, it is shown that the action of deaminase alone on porphobilinogen leads to release into the medium of the unrearranged hydroxymethylbilane ( 20), which ( a) ring closes chemically to uro'gen-I and ( b) is very rapidly converted by deaminase-cosynthetase into uro'gen-III. The biosynthetic role of this HOCH 2-bilane is studied, and the results show that deaminase is a builder of the unrearranged bilane system but is not a cyclizing enzyme. The work also shows that deaminase and cosynthetase have independent active sites but that they may work in close physical association. Finally, it is established that the tetrapyrrole macrocycle is assembled starting at ring A and building around to ring D.