When these hemoproteins turn over, the heme is not salvaged, but is degraded. New heme is synthesized for their replacements.
Heme is a member of a family of compounds called porphyrins .
Heme synthesis occurs partly in the mitochondria and partly in the cytoplasm. The process begins in the mitochondria because one of the precursors is found only there. Most of the intermediate steps are cytoplasmic. Summary of regulation of heme synthesis. Porphyrias are defects in porphyrin metabolism.