Heme iron in cytochromes and other heme-containing proteins (Heme iron)

Heme iron is a critical prosthetic group consisting of an iron ion coordinated within a protoporphyrin IX ring, found in a wide variety of hemoproteins including hemoglobin, myoglobin, and cytochromes (UniProt). It serves as a versatile redox center and gas-binding site, facilitating essential biological processes such as oxygen transport, electron transfer in the mitochondrial respiratory chain, and the metabolism of xenobiotics by cytochrome P450 enzymes (Wikipedia: Heme). In the context of pharmacology, heme iron is a primary target for antimalarial drugs like chloroquine, which interfere with the parasite's ability to detoxify free heme into inert hemozoin crystals (StatPearls: Antimalarial Medications). Additionally, heme iron is the site of action for potent toxins such as carbon monoxide and cyanide, which bind with high affinity to prevent oxygen transport or cellular respiration (NIH: Cyanide Poisoning). Understanding the coordination chemistry of heme iron is vital for developing therapies for blood disorders, infectious diseases, and poisoning (PubChem: Heme).

Other names

Iron protoporphyrin IXFerriprotoporphyrin IXHaem ironHeme groupHeme bHeme aHeme c

Heme iron acts as a coordination site for various ligands. Antimalarial drugs like chloroquine bind to ferriprotoporphyrin IX (heme) to prevent its biocrystallization into non-toxic hemozoin, leading to the accumulation of toxic free heme that causes parasite death (StatPearls). Toxicants like carbon monoxide and cyanide act as competitive or irreversible inhibitors; CO binds to heme iron in hemoglobin with higher affinity than oxygen, while cyanide binds to the heme a3 site in cytochrome c oxidase, halting the mitochondrial electron transport chain (NIH, PubMed).