to the histidine being ligated and it is not bound to copper iodide. In azurin, the Cysteine112 thiolate accepts the hydrogen bonds from the amide backbone of Asparagine47, and Phenylalanine114, and Histidine46 donates a hydrogen bond to the carbonyl backbone of Asparagine10. The Cysteine84 thiolate of plastocyanin accepts a hydrogen bond from a amide backbone, Asparagine38, and Histidine37 interacts strongly with the carbonyl backbone of Alanine33 and more weakly with the carbonyl backbone of Leucine5, Glycine34, and the amide backbone of Phenylalanine35. Blue Copper Protein "Entatic State" Cu2+ complexes normally have slow transfer rates. An example is the Cu2+/+ aquo, which is 5 x 10−7 M−1.sec−1 compared to the blue copper protein which is 1ms-01μs. Upon electron transfer the oxidized Cu2+ state at the blue copper protein active site will be minimized because the Jahn-Teller effect is minimized. The distorted geometry prevents Jahn-Teller distortion. The orbital degeneracy is removed due to the asymmetric ligand field. The asymmetric ligand field is influenced by the strong equatorial cysteine ligand and the weak axial methionine ligand. In Figure 2, an energy level diagram shows three different relevant geometries and their d-orbital splitting and the Jahn-Teller effect is shown in blue. (i) shows the tetrahedral geometry energy level diagram with a that is degenerate. The tetrahedral structure can undergo Jahn-Teller distortion because of the degenerate orbitals. (ii) shows the C3v symmetric geometry energy level splitting diagram with an 2E ground state that is degenerate. The C3v geometry was formed by the elongated methionine thioether bond at the reduced site. The unpaired electrons leads to the Jahn-Teller effect. (iii) shows the ground state energy level splitting diagram of the Cs geometry with a longer thioester bond and a subsequently shorter thiolate bond. This is the proper geometry of the blue copper protein. This shows that there is no presence of the Jahn-Teller effect. The energy diagram shows that the asymmetry of the short Cu-S(Cys) bond and the highly distorted Cu-L bond angles causes the degeneracy of the orbitals to be removed and thereby removing the Jahn-Teller effect, which is due to the weak donor at an Cu-S(Met) and strong donor at Cu-S(Met). See also Copper in health Stellacyanin References Peripheral membrane proteins