Blue copper proteins optical absorption

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

Type 2 Cu2+. This form of Cu is present in all the blue multi-copper oxidases. It is characterized by lacking sufficient optical absorption to be observed above that of the other Cu-chromophores in these molecules. Consequently it is sometimes referred to as the colorless Cu. Further, its EPR spectrum is similar to those exhibited by most small Cu2+ complexes. However, its presence is essential to the functioning of the multi-copper oxidases, and it has very unique chemical properties which distinguish it from Cu + bound to the non-blue Cu proteins. The T5q)e 2 designation should therefore be reserved for classification of the types of Cu2+ sites observed in the blue multi-copper oxidases, and it should not be used to classify the binding sites of non-blue copper proteins which have distinctly different chemical behavior. Thus, for example, any purported analogies between... 

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