The heme biosynthesis pathway involves eight enzymatic steps:
Condensation of glycine and succinyl-CoA to form δ-aminolevulinic acid (ALA). Formation of porphobilinogen from ALA. Condensation of four porphobilinogen molecules to form hydroxymethylbilane. Conversion of hydroxymethylbilane to uroporphyrinogen III. Decarboxylation of uroporphyrinogen III to coproporphyrinogen III. Oxidation of coproporphyrinogen III to protoporphyrinogen IX in the mitochondria. Oxidation of protoporphyrinogen IX to protoporphyrin IX. Insertion of ferrous iron into protoporphyrin IX to form heme.
