Metalloprotein

In biochemistry, a metalloprotein is a generic term for a protein that contains a metal cofactor. The metal may be an isolated ion or may be coordinated with a 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.

An important class of metalloproteins are metalloenzymes, these are enzymes that contain one or more metal atoms as functional parts of their structures. These metals are often involved in enzyme catalysis, such as in carbonic anhydrase and cytochrome c oxidase. Metal ions usually form part of the active site as they can be multicoordinated and thus held in a protein while having a high affinity for the substrate through a lone pair.