Heme (ferrous protoporphyrin IX) (None (commonly referred to as "heme" or "Fe(II)-heme" for the ferrous form))

Heme is a prosthetic group consisting of a protoporphyrin IX ring complexed with a central ferrous iron atom (Fe^2+^). It serves as a critical cofactor enabling oxygen transport in hemoglobin and myoglobin, electron transfer in cytochromes, and catalysis in a diverse range of enzymes (such as cytochrome P450s, peroxidases, and catalases). In its ferrous (Fe^2+^) state, heme can reversibly bind oxygen and other diatomic gases, enabling dynamic regulation of biological processes. The distinct redox and coordination chemistry of heme iron underlies its varied biological roles and makes it central to energy metabolism, oxidative defense, cellular signaling, and other processes. Defective heme synthesis or degradation contributes to diseases such as porphyrias, anemia, and certain toxicities. Free heme is highly reactive and potentially cytotoxic, emphasizing the need for tight physiological regulation. Note: "Heme/Ferrous Iron" is not a unique drug target but a foundational biochemical entity participating in the function of a vast array of biological proteins. Targeting heme or its metabolism affects a spectrum of pathways rather than a single molecular target.

Other names

Hemin (oxidized form, Fe^3+^)Ferroheme (heme with Fe^2+^, the biologically active form in oxygen binding)ProtohemeProtoporphyrin IX containing ferrous ironHeme b (the most common type in biology)

Drugs may provide hemin as a source to bypass heme synthetic blocks (e.g., in acute porphyria) Iron chelators reduce availability of ferrous iron for heme synthesis Induction or inhibition of heme-containing enzymes (e.g., cytochromes) alters drug metabolism