Copper binuclear sites

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... 

We first consider proteins containing a single type of a copper site starting with mononuclear ones. Subsequently, binuclear sites and multi-centered copper proteins will be discussed. 

The type-3 copper of hemocyanins and tyrosinases is usually EPR silent with the exception e.g. of Helixpomatia methemocyanin. Dopamine P-monooxygenase has been described to contain only type-2 copper according to EPR data but there seems kinetic evidence for a transient binuclear site... 

The several functions of ceruloplasmin cannot be explained at present. It seems reasonable that this diversity is related to the activity of the copper centres. The general pattern of oxidase activity is probably similar to that of the other blue oxidases, with a type 3 binuclear site serving to bind and reduce dioxygen, with electrons transferred from the type 1 site. The type 2 copper may represent a substrate-binding site. 

Kitagawa, Teizo and Ogura, Takashi, Oxygen Activation Mechanism at the Binuclear Site of Heme-Copper Oxidase Superfamily as Revealed by... 

The copper coordination geometry is also variable in this structural set. While mononuclear square-pyramidal sites are most common, mononuclear six-coordinate and even binuclear sites are also incorporated into the overall architectures. Water coordination is also evident, often giving rise to more than one coordination geometry in a material, as illustrated by 1, 4, 5 and 8. 

One of the major goals of studying active sites in copper proteins has therefore been to understand the spectroscopic features associated with the active site. This has led to a classification of three general types of copper protein active sites based on their unique spectral features Blue copper, normal copper and coupled binuclear copper. An additional class of copper proteins, the multi-copper oxidases, contains a combination of these three types of copper active sites. A reasonably firm understanding of the optical and EPR spectra of a number of copper proteins has now been achieved1,2K This article presents an overview of these electronic spectral features and their relationship to geometric and electronic structure. 

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. 

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