Coupled binuclear copper active site

A coupled binuclear copper active site is found in a variety of different metalloprotelns Involved in dloxygen reactions. These Include hemocyanln (reversible O- binding), tyrosinase (O2 activation and... 

SOLOMON Coupled Binuclear Copper Active Sites... 

Table 1. Proteins Containing Coupled Binuclear Copper Active Sites and Their Functions...

Our earlier research on the coupled binuclear copper proteins generated a series of protein derivatives in which the active site was systematically varied and subjected to a variety of spectroscopic probes. These studies developed a Spectroscopically Effective Model for the oxyhemocyanin active slte.(l) The coupled binuclear copper active site in tyrosinase was farther shown to be extremely similar to that of the hemocyanlns with differences in reactivity correlating to active site accessibility, and to the monophenol coordinating directly to the copper(II) of the oxytyroslnase site.(2) These studies have been presented in a number of reviews.(3) In the first part of this chapter, we summarize some of our more recent results related to the unique spectral features of oxyhemocyanin, and use... 

Some enzymes capable of oxidizing C-H bonds contain copper ions [52]. For example, tyrosinase [53a] contains a coupled, binuclear copper active site which reversibly binds dioxygen as a peroxide that bridges between the two copper ions. This enzyme catalyzes the orthohydroxylation of phenols with further oxidation of catechol to an ortho-quimne [53b-d], The mechanism proposed for phenolase activity of tyrosinase is shown in Scheme XI. 13 [521]. 

Tyrosinase is a copper-containing glycoprotein that carries a coupled binuclear copper active site capable of catalyzing two distinct reactions (i) hydroxylation of tyrosine to dihydroxyphenylalanin, i.e. dopa (cresolase activity), and (ii) subsequent two-electron oxidation to dopaquinone (catecholase activity) (227). Both reactions require oxygen and the enzyme, i.e. tyrosinase, in reduced cuprous form. Because of these two catalytic functions, tyrosinase is in modern terminology referred to as a mixed function oxidase (757). A mechanism (Fig. 3) for hydroxylation... 

Most of the synthetic models we found in our literature survey are concerned with hemocyanine, the oxygen transport protein in arthropods and molluscs, and tyrosinase, which catalyzes the two-electron oxidation of phenolic compounds. Both proteins contain a coupled binuclear copper active site, a Type III copper centre,"which reversibly binds dioxygen as peroxide bridging between the two copper ions" [153]. The Cu-Cu distance is of the order of 300-400 pm, and a tetragonal coordination is achieved with donor nitrogen atoms of imidazole ligands from histidine [142]. 

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