Copper metalloproteins redox

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

Enzymes containing amino acid radicals are generally associated with transition metal ions—typically of iron, manganese, cobalt, or copper. In some instances, the metal is absent it is apparently replaced by redox-active organic cofactors such as S -adenosylmethionine or flavins. Functionally, their role is analogous to that of the metal ion in metalloproteins. 

Hydroxyl radical may hydroxylate tyrosine to 3,4-dihydroxyphenylalanine (DOPA). DOPAs are the main residues corresponding to protein-bound reducing moieties able to reduce cytochrome c, metal ions, nitro tetrazolium, blue and other substrates (S32). Reduction of metal ions and metalloproteins by protein-bound DOPA may propagate radical reactions by redox cycling of iron and copper ions which may participate in the Fenton reaction (G9). Abstraction of electron (by OH or peroxyl or alkoxyl radicals) leads to the formation of the tyrosyl radical, which is relatively stable due to the resonance effect (interconversion among several equivalent resonant structures). Reaction between two protein-bound tyrosyl radicals may lead to formation of a bityrosine residue which can cross-link proteins. The tyrosyl radical may also react with superoxide, forming tyrosine peroxide (W13) (see sect. 2.6). 

Stellacyanin, the plastocyanins, and the azurins are the most widely studied copper-containing metalloproteins of the next active-site class, the Blue Copper sites. These proteins, which generally appear to be involved in redox chemistry, have quite unique spectral features32,33). The potential for complementary interaction between inorganic spectroscopy and protein crystallography is well demonstrated by the roles that they have played in generating fairly detailed geometric and electronic structural pictures of the Blue Copper metal centers. 

Metalloproteins, where the active site includes one or more metals, represent a very different class of proteins than those discussed above. The particular kinds of metalloproteins discussed here are those where the metal is redox active and represents a functional and not structural component of the system. Many mechanistic studies of metalloproteins have been carried out using radiation chemistry in the past 50 years. Two different ways of using radiation chemistry to query mechanisms will be illustrated here. The first, as described in the earliest of these studies using blue copper proteins such as azurin, involves using pulse radiolysis to change an oxidation state and thus... 

Small Redox Metalloproteins Blue Copper, Heme, and Iron-Sulfur Proteins... 

NO is ubiquitously placed as a moderately stable radical molecule. It is an intermediate in the natural redox cycles comprising the interconversion of nitrates to ammonia driven by bacteria containing iron or copper enzymes (namely, N02-, NO, or N20 reductases).4 Therefore, studies with metalloproteins and with adequately designed model complexes are of permanent interest for disclosing the diverse and complex mechanisms occurring in the biological systems.5... 

Cupredoxins refer to a group of copper proteins that share the same overall structural fold and perform biological electron transfer (ET) through their redox reactivity. The term cupredoxin comes from ferredoxin, the Fe-containing redox proteins. Cupredoxins comprise one of the three classes of metalloproteins known to carry out biological electron transfer, after cytochromes (see Chapter 8.2) and ferredoxins (see Chapter 8.3). 

One of the important roles of metalloproteins is electron transport between functional molecules in biological systems [39], Copper proteins are involved in electron transfer, redox reactions and the transport and activation of dioxygen. They are classified into Types I, II and III, and eir properties are as follows Type I One copper is involved in one unit. The copper has a strong absorption around 600 nm and small hyperfine coupling constants in ESR. It is called Blue copper protein. 

Other similar theoretical examinations of the role of bonding in the thermodynamics and other properties of redox metalloproteins have appeared. They include binuclear copper-A sites and cytochrome P450. ... 

A relatively large number of theoretical studies on the complete calculation of redox potentials of transition metal active sites in metalloproteins have been published. Metalloproteins studied include manganese superoxide dismutase, iron superoxide dismutase, copper-zinc superoxide dismutase, iron-sulfur proteins, cytochrome f, components of the photosynthetic reaction center, and peroxidases. ... 

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