Binuclear Cu site

Figure 4.91 presents the catalytic cycle of tyrosinase, an enzyme presently of commercial and industrial interest since it is involved in the browning of fruits in the presence of oxygen, due to the oxidation of the phenols catalyzed by this enzyme. The most important feature to note is that the enz5nne uses a binuclear Cu site able to bind a molecule of oxygen in a bridging mode. In contrast to the other monooxygenases, the two electrons required to split the molecule of... 

Chen P, Solomon EL 2004. O2 activation by binuclear Cu sites noncoupled versus exchange coupled reaction mechanisms. Proc Nat Acad Sci USA 101 13105-13110. 

The second class of dioxygen carriers is that of haemocyanins. These proteins, which contain a binuclear Cu(I) site (thus in the oxidized Cu(II) met form they belong to the so-called Type 3 copper proteins , which contain an EPR-silent dicopper active site), regulate dioxygen transport in the respiration of arthropods and molluscs. Figures 7 and 8 show... 

Each methylenediphosphonate chelates not only to the Cu(II) site but also to one molybdenum center to produce a MoCu(03PCH2P03) subunit. The remaining two oxygen atoms link the diphosphonate to two molybdenum sites. Consequently, each diphosphonate ligand bonds to three binuclear Mo sites. In contrast to the structure of 9, all of the oxygen atoms of the methylenediphosphonate ligand of 12 are involved in bonding. 

A series of hemocyanin and tyrosinase active site derivatives (Fig. 23) can be prepared61"66), allowing systematic variation of the binuclear copper active site and chemical perturbation for spectral studies. In the simplest derivative, met-apo, one copper has been removed and the remaining copper oxidized to the spectroscopically accessible Cu(II). Next in complexity is a mixed-valent binuclear copper site. The Cu(II), in this half-met derivative, exhibits open-shell d9 spectroscopic features and the Cu(I), though spectroscopically inaccessible, can still be studied by comparison to the met-apo derivative. Two derivatives have formally binuclear cupric sites met, which is EPR-non-detect-able, and dimer, which exhibits an intense broad EPR signal. Spectroscopic study of these derivatives has led to the present picture of the coupled binuclear copper protein active site shown at the bottom of Fig. 23. 

The type 3 binuclear Cu(II) pair in an MCO is characteristic of this type of copper site in biology. First, both copper atoms are ligated by three protein side chains each all six are His residues. Five of the imidazoles coordinate the Cu(II) atoms via the Ne2 nitrogens while the sixth His does so via N51. This coordination pattern is a conserved feature of the MCO structure.Second, the two Cu(n)... 

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