Biologic Copper Sites and the Multicopper Oxidases

Copper proteins are classified on the basis of the type of copper site that they contain. There are three types of copper sites (Solomon and Lowery, 1993). They differ as to coordination number, type of ligand, and geometry these differences in turn are the basis for these sites electronic signatures and chemical (redox) activity. Type 1 Cu(II) exhibits a very strong absorbance at 600 nm(s = 5000 cm ). This absorbance 

Type 3 copper is the third type of Cu(ll) site in biology. A type 3 site has two distinguishing electronic properties. First is its relatively strong absorbance in the near-UV at 330 nm(s = 3—5000 cm ). This transi- 

What distinguishes multicopper oxidases from other copper proteins is that they contain one each of these three types of copper site (Solomon and Lowery, 1993 Solomon et al., 1996). Not only does this make them excellent models for all copper proteins, but because they have four redox-active metal ions, they also serve as paradigms for other enzymes that couple a one-electron reductant to a four-electron oxidant, most notably cytochrome c oxidase. Indeed, the three copper sites (and four copper atoms) in the multicopper oxidases play essentially equivalent roles in comparison to the two heme groups and two copper atoms in cytochrome c oxidase. 

Despite large differences in their overall sequence and resulting structure, the multicopper oxidases contain signature sequences for these 

Spectral data for the Fet3 protein illustrate the electronic properties of the three types of Cu(II) sites found in multicopper oxidases (Blackburn et al., 2000 Hassett et al., 1998). The cwEPR spectrum shown in Fig. 2 for 

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