In biochemistry, a metalloprotein is a generic term for a protein that also contains a metalcofactor. The metal may be an isolated ion or may be coordinated with an nonprotein organic compound, such as the porphyrin found in hemoproteins. In some cases, the metal is co-coordinated with a side chain of the protein and an inorganic nonmetallic ion. This kind of protein-metal-nonmetal structure is seen in iron-sulfur clusters.