<P> Heme or 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 ." The definition is loose, and many depictions omit the axial ligands . Many porphyrin - containing metalloproteins have heme as their prosthetic group; these are known as hemoproteins . 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 . </P> <P> The word heme is derived from Greek αἷμα haima meaning blood . </P>

To what group of organic compounds does hemoglobin belong