what is heme

Heme, also spelled haem, is a coordination complex consisting of an iron ion coordinated to a porphyrin acting as a tetradentate ligand, and to one or two axial ligands. It is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. Heme is a porphyrin compound, with a central iron atom chelated by four nitrogen atoms. It is found in every living plant and animal, most abundantly in animals. Heme is what makes meat taste like meat, and it is an essential molecule that contains iron. It is naturally found in fairly high concentrations in the blood of humans and other animals, and in much lower concentrations in plants. Heme is also what makes blood red, makes meat pink, and gives blood a subtle metallic flavor.