Heme (iron(II)-protoporphyrin IX) (Heme b)

Heme (iron(II)-protoporphyrin IX) is a planar tetrapyrrole macrocyclic structure, central to the function of hemoproteins including hemoglobin, myoglobin, and cytochromes. Heme functions as an essential prosthetic group, allowing proteins to bind and transport oxygen, participate in electron transfer for cellular respiration, and catalyze metabolic reactions through its redox-active iron ion. It is synthesized from protoporphyrin IX by insertion of ferrous iron by ferrochelatase. Biological roles for heme extend beyond enzymatic support to signaling, regulation of circadian rhythms, and gene expression. Imbalances in heme or protoporphyrin IX metabolism result in a spectrum of diseases from anemia to the porphyrias and photosensitive conditions defined by toxic protoporphyrin IX buildup. Though not a classic pharmacological target like a receptor or enzyme, heme and its precursor are vital in many therapeutic, diagnostic, and disease mechanisms.

Other names

HemeHaemiron-protoporphyrin IXprotoheme IXferrohemeheme bFe(II)-protoporphyrin IXhemin (when oxidized)protoporphyrin IX (without iron)

As a photosensitizer in photodynamic therapy (PDT), protoporphyrin IX accumulates in cells and produces reactive oxygen species upon illumination. Enzymatic cofactor enabling electron transfer, redox reactions, oxygen binding/release, and catalysis. Iron chelation and sequestration.