Copper proteins and copper enzymes

The copper proteins that function in homeostasis, electron transport, dioxygen transport and oxidation are discussed. Particular emphasis is placed on the role of the ligands, their type and disposition which, in conjunction with other residues in the active site, determine the role of the copper ion. It is proposed that copper proteins can be considered in four groups. Those in Group I contain a single copper ion in an approximately tetrahedral environment with nitrogen and sulphur-containing ligands. Group II proteins have a single copper ion in a square-planar-like arrangement. Group III proteins have two copper ions in close proximity. Group IV consists of multi-copper proteins, composed of sites representative of the other three groups.