Dioxygen binding copper enzymes

Evidence tom a variety of sources indicates that the active site of tyrosinase is very similar to that of hemocyanin, a dioxygen-binding protein found in molluscs and arthropods (15,16). This type of active site contains two copper ions, which are cuprous in the deoxy state, and which reversibly bind dioxygen, forming the oxy form of the enzyme or protein in which a peroxy ligand bridges between two cupric ions. 

The enzyme requires two copper ions per subunit for full expression of activity (18), but, unlike tyrosinase and hemocyanin, there is an absence of magnetic coupling between the two Cu(II) sites and both appear to be separate, isolated mononuclear copper sites (17). The process of dioxygen binding and activation appears to involve interaction of the doxygen molecule with only one copper ion, and it is also found that a proton is requir for the hydroxylation of substrate (19). 

Figure 1 Schematic representation of the dioxygen binding dinuclear copper enzymes Hemocyanin (He), Tyrosinase (Tyr), and Catechol oxidase (Co)...

Both enzymes contain two Cu atoms and in the case of PMH (Figure 14.5) it has been established that dioxygen binds to one of the two type 2 copper atoms in an end-on mode . A copper—dioxygen complex has been... 

Prigge ST, Eipper BA, Mains RE, Amzel LM. 2004. Dioxygen binds end-on to mononuclear copper in a precatalytic enzyme complex. Science 304 864-867. 

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