Heme (protoporphyrin IX iron complex)

Heme cofactor refers to a planar organic compound, protoporphyrin IX complexed with an iron ion, acting as an essential non-protein prosthetic group in diverse proteins. It enables oxygen binding and electron transfer, is indispensable in hemoglobin (blood oxygen transport), myoglobin (muscle oxygen storage), cytochromes (mitochondrial electron transport), catalases/peroxidases (ROS breakdown), and cytochrome P450s (drug metabolism). As a cofactor, heme itself is not a therapeutic target; however, proteins containing heme (hemoproteins) are common pharmacological targets. Free heme released during hemolysis or excessive synthesis can lead to oxidative and inflammatory injury. Heme functions as both a catalytic center and a regulatory ligand, influencing a wide array of biological and pathological processes[1][4][5][7][8][9]. In summary: "Heme cofactor" is not a protein, receptor, or classical drug target, but a chemical entity found in many druggable protein targets (hemoproteins); thus, it is incorrect to list heme cofactor as a therapeutic molecular target.

Other names

HemeFe-protoporphyrin IXIron-porphyrin complexProsthetic group hemeHemin (oxidized form used therapeutically)

Direct binding to heme iron atom, altering protein function (e.g., inhibition of cytochrome P450s by azoles) Modulation of redox state (many drugs/agents can oxidize or reduce heme iron in hemoproteins) Competitive binding (carbon monoxide, NO, cyanide compete with oxygen at heme iron)