Electron transport, blue copper proteins

Electron-transferring subunit, nickel-containing hydrogenases, 38 409-410 Electron transport blue copper proteins, 36 378 NiFe hydrogenase, 47 16-17 Electron volt, 16 73... 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

BLUE COPPER PROTEINS INVOLVED IN ELECTRON TRANSPORT... 

Blue Copper Proteins Involved in Electron Transport. 

Most mechanisms which control biological functions, such as cell respiration and photosynthesis (already discussed in Chapter 5, Section 3.1), are based on redox processes. In particular, as shown again in Figure 1, it is evident that, based on their physiological redox potentials, in photosynthesis a chain of electron carriers (e.g. iron-sulfur proteins, cytochromes and blue copper proteins) provides a means of electron transport which is triggered by the absorption of light. 

Finally, we examine azurin, a blue protein (FW = 14 000) devoted to bacterial electron transport, the copper centre of which has a penta-coordinate trigonal bipyramidal geometry, at variance with all the other cupredoxins, Figure 39.73... 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

Copper proteins are involved in a variety of biological functions, including electron transport, copper storage and many oxidase activities. A variety of reviews on this topic are available (Sykes, 1985 Chapman, 1991). Several copper proteins are easily identified by their beautiful blue colour and have been labelled blue copper proteins. The blue copper proteins can be divided into two classes, the oxidases (laccase, ascorbate oxidase, ceruloplasmin) and the electron carriers (plastocyanin, stellacyanin, umecyanin, etc.). 

The plastocyanins are blue copper proteins found in the chloroplasts of higher plants and algae where they mediate electron transport between cytochrome f and P-700 (Barber, 1983 Haehnel, 1984, 1986 Cramer etal., 1985 Sykes, 1985 Andersen et al., 1987). Plastocyanins each contain one copper bound by a single polypeptide chain of molecular weight around 10500 (Sykes, 1985). The spectroscopic properties of the copper are those of a typical blue site. The properties of the plastocyanins have been the subject of detailed reviews (Sykes, 1985 Haehnel, 1986 Chapman, 1991). 

Electron transport between cubane [Fe4S4] clusters, cytochrome c, or Cu + centers in blue copper proteins " and the periphery of the proteins has been examined by complexing ruthenium species to surface histidines. In the case of the iron sulfur cubane in Chromatium vinosum, four surface histidines served as points of ruthenium attachment. The rates of electron transport from the Fe4S4 core to ruthenium varied over two orders of magnitude and were used to diagnose the preferred channel for electron transport. Cysteine and lysine residues have also been used as binding sites in studies of cytochrome c and cytochrome P450 cam proteins. 

Of the other blue copper proteins, only amicyanin shows a similar effect of pH (79), and a TpK of 7.18 has been obtained for the Cu(I) state. As with plastocyanin, no corresponding effect is observed for Cu(II) amicyanin, at least down to pH 4.5. The physiological relevance in the case of both proteins is at present unclear. Because in photosynthesis the pH of the inner thylakoid is less than 5.0, one possibility is that this is related to proton transport. Alternatively, it quite simply may be a control mechanism for electron transport. 

Rusticyanin is an abundant, highly stable periplasmic blue copper protein (e.g., Cobley and Haddock 1975 Jedlicki et al. 1986 Ronk et al. 1991 Nunzi et al. 1993 Blake et al. 1993). Studies of rusticyanin include kinetic competence in the iron oxidation reaction (Blake and Shute 1994), identification of a His ligand to the copper center (Casimiro et al. 1995), a solution NMR structure (Botuyan et al. 1996), and a high-resolution X-ray structure (Walter et al. 1996). Rusticyanin forms a complex with new c-type heme cytochrome in iht A. ferrooxidans electron transport chain (Giudici-Orticoni et al. 2000). 

Type 1 Blue Copper Proteins — Electron Transport... 

Cu 72 Electron transfer systems (blue copper proteins) O2 storage and transport (haemocyanin) Cu transport proteins (ceruloplasmin)... 

Blue copper proteins contain a minimum of one Type 1 Cu centre, and those in this class include plastocyanins and azurins. Plastocyanins are present in higher plants and blue-green algae, where they transport electrons between Photosystems I and II (see above). The protein chain in a plastocyanin comprises between 97 and 104 amino acid residues (most typically 99) and has 10 500. Azurins occur in some bacteria and are involved in electron transport in the conversion of [N03] to N2. Typically, the protein chain contains 128 or 129 amino acid residues (M 14600). 

Blue copper proteins (also known as type 1 Cu proteins or cupredox-ins), involved in biological electron transport, share a common structural motif, in which a Cu " ion is trigonally coordinated by a pair of histidine side chains and a cysteine thiolate ligand (Fig. 14). A methionine S atom is found along the trigonal axis at a long distance, 2.6-3.1... 

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. 

This copper(II) mononuclear complex is responsible for some remarkable properties, one of which is the high redox potentials of the copper(II) ions in these environments. These blue-copper proteins are engaged in electron transport, which involves a switching of the oxidation state of copper between +2 and + ... 

Numerous biological redox systems have been studied by the spectroelectrochemical approach, including cytochromes, myoglobin, photosynthetic electron transport components, spinach ferrodoxin, blue copper proteins, retinal, and vitamin B 2 analogues. Two classic examples are presented here. 

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