The deep red, oxygen-carrying, nonprotein, ferrous component of hemoglobin. Also called reduced hematin.
The deep red, nonprotein, iron-containing component of hemoglobin that carries oxygen. Heme is a porphyrin with an iron atom at its center. One of the free valence electrons of the iron atom of heme is bound to the hemoglobin molecule, while the other is available for binding to an oxygen atom. A hemoglobin molecule contains four hemes. Chemical formula: C34H32FeN4O4.