found in cytochrome c oxidase and nitrous-oxide reductase (). The two copper atoms are coordinated by two histidines, one methionine, a protein backbone carbonyl oxygen, and two bridging cysteine residues. Copper B centres (CuB) are found in cytochrome c oxidase. The copper atom is coordinated by three histidines in trigonal pyramidal geometry. A tetranuclear Copper Z centre (CuZ) is found in nitrous-oxide reductase. The four copper atoms are coordinated by seven histidine residues and bridged by a sulfur atom. Blue copper proteins The blue copper proteins owe their name to their intense blue coloration (Cu(II)). The blue copper protein often called as “moonlighting protein”, which means a protein can perform more than one function. They serve as electron transfer agents, with the active site shuttling between Cu(I) and Cu(II). The Cu2+ in the oxidized state can accept one electron to form Cu1+ in the reduced protein. The geometry of the Cu center has a major impact on its redox properties. The Jahn-Teller distortion does not apply to the blue copper proteins because the copper site has low symmetry that does not support degeneracy in the d-orbital manifold. The absence of large reorganizational changes enhances the rate of their electron transfer. The active site of a type-I blue copper protein. Two 2-histidines, 1 methionine and 1 cysteine present in the coordination sphere. Example for Type-I blue copper protein are plastocyanine , azurin, and nitrite reductase, haemocyanin and tyrosinase . Structure of the Blue Copper Proteins Type I Copper Centers The Blue Copper Proteins, a class of Type 1 copper proteins, are small proteins containing a cupredoxin fold and a single Type I copper ion coordinated by two histidine N-donors, a cysteine thiolate S-donor and a methionine thioether S-donor. In the oxidized state, the Cu+2 ion will form either a trigonal bipyramidal or tetrahedral coordination. The Type 1 copper proteins are identified as blue copper proteins due to the ligand to metal charge transfer an intense band at 600 nm that gives the characteristic of a deep blue colour present in the electron absorption spectrum. The protein structure of a Type 1 blue copper protein, amicyanin, is built from polypeptide folds that are commonly found in blue copper proteins β sandwich structure. The structure is very similar to plastocyanin and azurin as they also identify as Type 1 copper proteins. They are also similar to one another due to the geometry of