Type 1 Blue Copper Proteins — Electron Transport

Type 1 Blue Copper Proteins — Electron Transport 

An important concept in enzymology is that while catalysis involving bond cleavage and formation requires conformational change, and is relatively slow (maximum 10 s ), electron transfer is much more rapid (10 s ), which does not allow much time for conformational change  

Whereas enzyme catalysis invariably involves movement and conformational change, in electron transfer, which is orders of magnitude faster, there is no time for movement. 

FIGURE 14.2 (a) X-ray structure of poplar plastocyanin from poplar leaves, as a ribbon diagram with its ligands highlighted. PDB code IPLC. 

A number of other Cu electron transfer proteins which contain type-1 Cu centres (azurin, cemloplasmin, laccase, nitrite reductase, msticyanin, and stellacyanin) are known. They aU have three coordination positions contributed by 2 His and one Cys, similar to the copper coordination chemistry in plastocyanin — yet they span 

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The mononuclear blue (or type 1) copper proteins (cupredoxins) see Copper Proteins with Type 1 Sites), involved in biological electron transport, share a common structural motif, in which the single Cu(ll) ion is tightly bound ( 1.9-2.2 A) to two histidine and one cysteine ligand... 

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). 

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). 

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. 

Copper-proteins are wide-spread in both animals and plants and have been related to many metabolic processes, as oxygen transport, electron transfer and hydroxylation Copper-containing sites are usually classified in three different types " the type 1, or blue center is characterized by a combination of properties that has not yet been reproduced in model complexes (an intense absorption band at 600 nm, a very small copper hyperfine coupling constant A and a high positive redox potential for the Cu(II)/ Cu(I) couple) the type 2, or non-blue center has properties comparable to those of low molecular weight cupric complexes the type 3 consists of an antiferromagnetically coupled copper(II) pair. 

Small blue proteins are involved in various biochemical processes. Where their physiological function is known, it is that of single-electron transport proteins. The range of their redox potentials reaches from +183 mV (Halocyanin [18], + 184 mV Stellacyanin [68] to 680 mV (Rusticyanin [68, 69]) as compared to Cu2+/Cu+, E° = +153 mV. Very few redox proteins function in this range. This feature, and their characteristic blue color are the product of the type 1 copper center, the only redox-active group in these proteins. During electron... 

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