Incorporation of iron into protoporphyrin (PPIX) catalyzed by ferrochelatase to form heme
A word about subcellular localization:
Heme synthesis occurs partly in the mitochondria and partly in the cytoplasm. The process begins in the mitochondrial matrix with the synthesis of 5-aminolevulinic acid (ALA) from succinyl-CoA and glycine catalyzed by the enzyme 5-aminolevulinate synthase (ALAS). ALA molecules then enter the cytoplasm where they are combined to form the monopyrrole porphobilinogen (PBG). A series of linked reactions leads to generation of tetrapyrrole coproporphyrinogen III, which is then transported back into the mitochondria for further modification by coproporphyrinogen oxidase (CPOC) and protoporphyrinogen oxidase (PPOX), and finally iron is inserted by ferrochelatase (FECH). Learn more here.
