The two staing materials of heme synthesis pathway are succinyl CoA and glycine. Pyridoxal phosphate is needed to activate glycine. ALA synthase catalyzes the conversion of succinyl CoA and glycine to delta aminolevulinate. This is the rate limiting enzyme in porphyrin biosynthesis in the mammalian liver. Synthesis of ALA occurs in mitochondria. Last 3 steps of heme synthesis occur in the cytoplasm. The 3 enzymes which catalyse the reactions in cytoplasm are ferrochelatase, protoporphyrinogen oxidase and coproporphyrinogen oxidase. Coproporphyrinogen oxidase catalyze conversion of coproporphyrinogen III to protoporphyrinogen III. Protoporphyrinogen oxidase catalyze conversion of protoporphyrinogen III to protoporphyrin III. Ferrochelatase catalyze conversion of protoporphyrin III to heme by incorporating heme into protoporphyrin. Ref: Murray R.K. (2011). Chapter 31. Porphyrins & Bile Pigments. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds),Harper's Illustrated Biochemistry, 29e.