Hemoproteins have diverse biological functions including the transportation of diatomic gases, chemical catalysis, diatomic gas detection, and electron transfer. The large semi-transparent sphere indicates the location of the iron ion. Color scheme: grey=iron, blue=nitrogen, black=carbon, white=hydrogen, red=oxygen Function The heme group of succinate dehydrogenase bound to histidine, an electron carrier in the mitochondrial electron transfer chain. Space-filling model of the Fe- protoporphyrin IX subunit of heme B. The word haem is derived from Greek αἷμα haima meaning "blood". Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase. Among the metalloporphyrins deployed by metalloproteins as prosthetic groups, heme is one of the most widely used and defines a family of proteins known as hemoproteins. In biochemical terms, heme 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." The definition is loose, and many depictions omit the axial ligands. Heme is biosynthesized in both the bone marrow and the liver. Heme ( American English), or haem ( Commonwealth English, both pronounced / hi:m/ HEEM), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Chemical coordination complex of an iron ion chelated to a porphyrin Binding of oxygen to a heme prosthetic group.
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