Electron transfer metalloproteins

Alessandrini A, Comi S, Facci P (2006) Unravelling single metalloprotein electron transfer by scanning probe techniques. Phys Chem Chem Phys 8 4383 1397... 

Just as CoIIl-phenanthroline complexes have been used in metalloprotein electron transfer studies (vide supra), Yount and coworkers have utilized [CoC03(phen)2]+ and CoCl2 in the presence of phenanthroline to block the ATPase activity of myosin, and attachment to sulfhydryl groups near the active site is suggested.321... 

Davis, J.J., Bruce, D., Canters, G.W., Crozier, J., and Hill, H.A.O. (2003) Genetic modulation of metalloprotein electron transfer at bare gold. Chemical Communications, 576-577. 

Measurements of the rates of oxidation-reduction reactions began in the late 1940s. A great deal of the early experimental work was carried out by inorganic chemists, and by the 1970s the reactivity patterns of many complexes had been uncovered." Chemists studying the mechanisms of metalloprotein electron-transfer reactions frequently seek parallels with the redox behavior of less-complicated inorganic complexes. 

Because the enthalpies and entropies of metalloprotein electron transfer processes are influenced by changes in protein conformation and solvation, as well as by other structural and medium effects (5, 165, 166), comparison of these parameters over a range of HiPIPs differing by single-point mutations affords considerable insight into the factors underlying cluster redox chemistry. 

The investigation of the kinetics and mechanisms of electron transfer reactions between metalloproteins and with inorganic redox reactants continues to be a rapidly growing field. The Proceedings of the 3rd International Conference on Bioinorganic Chemistry (1987) have been published in a special issue of Recueil des Travaux Chimiques des Pay-Bas, and include a section on metalloprotein electron transfer. The subject of long-distance electron transfer in metalloproteins has also been reviewed. 

Computer simulations of electron transfer proteins often entail a variety of calculation techniques electronic structure calculations, molecular mechanics, and electrostatic calculations. In this section, general considerations for calculations of metalloproteins are outlined in subsequent sections, details for studying specific redox properties are given. Quantum chemistry electronic structure calculations of the redox site are important in the calculation of the energetics of the redox site and in obtaining parameters and are discussed in Sections III.A and III.B. Both molecular mechanics and electrostatic calculations of the protein are important in understanding the outer shell energetics and are discussed in Section III.C, with a focus on molecular mechanics. 

Therlen MJ, Chang J, Raphael AL, Bowler BE, Gray HB (1991) Long-Range Electron Transfer in Metalloproteins. 75 109-130... 

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. 

Fedurco M. 2000. Redox reactions of heme-containing metalloproteins Dynamic effects of self-assemhled monolayers on thermod3mamics and kinetics of c)dochrome c electron-transfer reactions. Coord Chem Rev 209 263-331. 

Outer-sphere electron transfer reactions involving the [Co(NH3)6]3+/2+ couple have been thoroughly studied. A corrected [Co(NH3)6]3+/2+ self-exchange electron transfer rate (8 x 10-6M-1s-1 for the triflate salt) has also been reported,588 which is considerably faster than an earlier report. A variety of [Co(NH3)g]3+/2+ electron transfer cross reactions with simple coordination compounds,589 organic radicals,590,591 metalloproteins,592 and positronium particles (electron/ positron pairs)593 as redox partners have been reported. 

H.B. Gray and B.G. Malmstrom, Long-range electron transfer in multisite metalloproteins. 

Studies on 1 1 electron-transfer reactions of metalloproteins with inorganic complexes are, in a number of cases, at a stage where the site or sites on the protein at which electron transfer occurs can be specified. 

Metalloproteins fall into three main structure categories depending on whether the active site consists of a single coordinated metal atom, a metal-porphyrin unit, or metal atoms in a cluster arrangement. In the context of electron-transfer metalloproteins, the blue Cu proteins, cytochromes, and ferre-doxins respectively are examples of these different structure types. Attention will be confined here mainly to a discussion of the reactivity of the blue Cu protein plastocyanin. Reactions of cytochrome c are also considered, with brief mention of the [2Fe-2S] ferredoxin, and high potential Fe/S protein [HIPIP]. 

It is timely to review the reactivity of plastocyanin in the light of recent aqueous solution studies, and the elegant structural work of Freeman and colleagues on both the PCu(I) and PCu(II) forms (1 2) Plastocyanin now ranks alongside cytochrome c (3) as the electron-transfer metalloprotein for which there is most structural information. 

The aim in solution studies on metalloprotein is to be able to say more about intermolecular electron transfer processes, first of all by studying outer-sphere reactions with simple inorganic complexes as redox partners. With the information (and experience) gained it is then possible to turn to protein-protein reactions, where each reactant has its own complexities... 

Rate Constants and Reactivity. Electron-transfer reactions of plastocyanin (and other metalloproteins) are so efficient that only a narrow range of redox partners (having small driving force) can be employed. Rates are invariably in the stopped-flow range, Table I. Unless otherwise stated parsley plastocyanin... 

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