Blue copper proteins azurin

This discussion of copper-containing enzymes has focused on structure and function information for Type I blue copper proteins azurin and plastocyanin, Type III hemocyanin, and Type II superoxide dismutase s structure and mechanism of activity. Information on spectral properties for some metalloproteins and their model compounds has been included in Tables 5.2, 5.3, and 5.7. One model system for Type I copper proteins39 and one for Type II centers40 have been discussed. Many others can be found in the literature. A more complete discussion, including mechanistic detail, about hemocyanin and tyrosinase model systems has been included. Models for the blue copper oxidases laccase and ascorbate oxidases have not been discussed. Students are referred to the references listed in the reference section for discussion of some other model systems. Many more are to be found in literature searches.50... 

The blue copper proteins azurin, plastocyanin, stellacyanin, and umecyanin incorporate Cu bound to a combination of N/thiolate/thioether ligands. An important feature of these metalloenzymes is the facile copper(II)/(I) couple that these species exhibit, which is linked to the highly strained, asymmetric coordination geometry at the metal center. The synthesis of model complexes for these so-called Type 1 copper proteins has been reviewed. ... 

Metalloproteins that have been overexpressed may need to be reconstituted with their native metal(s). For example, overexpression of the blue copper protein azurin results in a mixture of apo- and Zn forms. When a gene of an uncharacterized metalloprotein is expressed, care must be taken to assure that the identity of the native metal is determined through studies of native protein. Overexpression of heme proteins typically requires reconstitution with hemin. In the case of c-type heme, the heme must be attached covalently to the polypeptide with the assistance of cellular machinery. Wide success in expressing a range of c-heme containing proteins has been achieved by expression of both the structural cytochrome gene and the apparatus for protein maturation. ... 

Figure 4 Cd PAC data—example, (a) Experimentally determined perturbation function that contains the information on the local structure and dynamics at the PAC probe site (data points with error bars and fit (fiiU line)).(b) Fourier transform of the experimental data (red) and of the fit (blue). This dataset was recorded for the cadnumn-substituted blue copper protein azurin. (After Figure 6 in )...

Chi, Q.J., Zhang, J.D., Andersen, J.E.T., and Ulstrup, J. (2001) Ordered assembly and controlled electron transfer of the blue copper protein azurin at gold (111) single-crystal substrates. Journal of Physical Chemistry B, 105,... 

Interfadal Electrochemical Organization and Electron Transfer of the Blue Copper Protein Azurin - a Nanoscale Bioelectrochemical Paradigm... 

The application of direct electrochemistry of small redox proteins is not restricted to cytochrome c. For example, the hydroxylation of aromatic compounds was possible by promoted electron transfer from p-cresol methylhydroxylase (a monooxygenase from Pseudomonas putida) to a modified gold electrode [87] via the blue copper protein azurin. All these results prove that well-oriented non-covalent binding of redox proteins on appropriate electrode surfaces increases the probability of fast electron transfer, a prerequisite for unmediated biosensors. Although direct electron-transfer reactions based on small redox proteins and modified electrode surfaces are not extensively used in amperometric biosensors, the understanding of possible electron-transfer mechanisms is important for systems with proteins bearing catalytic activity. 

The arsenite oxidase is a molybdenum-containing hydroxylase (63,64) with two [Fe-S] centers (see Fig. 8). It is found in the periplasmic space between the inner and outer membranes of Alcaligenes, coupled via the small blue copper protein azurin to cytochrome c (63). Arsenite oxidase consists of a large subunit... 

Strong pH dependencies of the rates of reduction of a number of cytochromes c and the blue copper protein azurin by ascorbic acid are interpreted in terms of reaction of the ascorbate anion rather than highly reactive deprotonated forms of the proteins since it is unlikely that all the proteins would act in a similar fashion. The second-order rate constants for the ascorbate " anion increase with increasing positive charge on the protein consistent with an outer-sphere mechanism. This is confirmed by cyt c(iii) where the rate of reduction by ascorbate exceeds the limiting rate of substitution of methionine-80 by imidazole at pH 9.0 (7=0.1 M, 21 °C), 8 s" Activation parameters are similar to those of other outer-sphere reactions between proteins and small-molecule redox agents. 

Electron transfer in biological systems where the electron donor and acceptor are separated by a long molecular distance is encountered in very important processes such as photosynthesis and respiration [54]. As natural systems are not appropriate for such studies. Gray et al. have employed proteins chemically labeled with transition metal complexes to measure ET rates in metaUoproteins. In particular, they have shown that long-lived luminescent probes enabled a wider range of ET measurements than is possible with non-luminescent complexes [55]. The blue copper protein azurin is a convenient model for the study of ET in p-sheet proteins. 

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