Fig. 1

Heme synthesis pathway in animal cells. ALA is synthesized by the condensation of glycine and succinyl CoA via mitochondrial ALA synthase. The polymerization of 8 molecules of ALA in several subsequent steps produces protoporphyrin IX (PpIX). Heme is synthesized by the insertion of a ferrous ion into PpIX, and incorporated into proteins to produce heme-proteins such as hemoglobin, cytochrome, and P450