Type 4 Copper Sites

2 Type 2 Copper Sites. - Mononuclear proteins with Cu(II) in a nearly 

Galactose oxidase (pdb 1GOF) Amine oxidase (pdb ID6Z) 

There are numerous reports on the chemical synthesis of models for the active site of galactose oxidase both in the reduced Cu(l) and the oxidized Cu(II) form. We mention only a selection in which EPR is at least used to characterize the complex either on the phenoxy radical or on the copper part, typically in conjunction with X-ray data.48,49 50 A review on structural, spectroscopic and redox aspects of galactose oxidase models is available.51 More important with respect to EPR is the report on the 3-tensor calculation of the thioether substituted tyrosyl radical by ab initio methods but this is borderline to the aspects treated in this review since the copper ion is not involved.52 

Copper-zinc SOD can also act as a peroxidase at high pH. At physiological pH-values, this process involves bicarbonate. The precise role of the latter ions is 

A similar connection between copper coordination to peptides and medical consequences exists for the Alzheimer disease.79 The amyloid-p peptide in senile plaque is the site of copper binding and as before there is interest to study details of the coordination and the stability. The neurotoxicity seems to be related to free radical damage and Cu2+ chelators are probed as therapy. So far, there seems to be no investigation at a resolution possible to pinpoint copper ligands as derived from ENDOR or related pulse techniques. We mention some relevant EPR studies as introductory sources into the topic.80 81,82 

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Evidence from pulse radiolysis experiments for electron transfer from the type 1 to the type 2 copper site in A. cycloclastes NiR has been... 

Addition of reducing equivalents causes complete loss of the EPR signal (Figure 2), which reappears rapidly and completely upon reoxidation with dioxygen or ferricyanide. Structural changes of the type 1 and type 2 copper sites can be conveniently monitored by the EPR technique. Thus, after lyophilization of the pure enzyme in phosphate... 

Figure 4 Type-2 copper site in gaiactose oxidase from Dactylium dendroides (PDB-code 1GOG) prepared with PyMOL (W. L. Delano, Paio Aito, 2003).

The physiological electron donors for NIR are either the cupredoxins pseudoazurin or azurin depending on the organism. Pseudoazurin, for example, reduces the type-1 copper and subsequently the electron is transferred to the type-2 copper site, which is also the binding site for nitrite. Nitrite is bound to the type-2 copper site as demonstrated by electron nucleus double resonance studies on NIR from Achromohacter xylosoxidans and in a crystal structure of the complex between nitrite and NIR from A. cycloclastes The crystal structure of the complex shows that nitrite binds asymmetrically with the oxygens toward the copper. 

Kataoka K, Furusawa H et al (2000) Functional analysis of conserved aspartate and histidine residues located around the type 2 copper site of copper-containing nitri reductase. J Biochem 127 345-350... 

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