Proteins electron transfer reactions

In order to probe these effects, a number of studies on the kinetics of electron transfer between small molecule redox reagents and proteins, as well as protein-protein electron transfer reactions, have been carried out (38-41). The studies on reactions of small molecules with electron transfer proteins have pointed to some specificity in the electron transfer process as a function of the nature of the ligands around the small molecule redox reagents, especially the hydrophobicity of these... 

Miyashita, O. and Go, N. (2000) Reorganization energy of protein electron transfer reaction study with structural and frequency signature, J. Phys. Chem. 104, 7516-7521. 

Onuchic, J. N., Beratan, D. N., Winkler, J. R. and Gray, H. B., 1992, Pathway analysis of protein electron-transfer reactions Ann. Rev. Biophys. Biomol. Struct. 21 3499377. 

Kinetic Complexity of Protein Electron Transfer Reactions... 

APPLICATION OF MARCUS THEORY TO OTHER PROTEIN ELECTRON TRANSFER REACTIONS... 

Electron carriers and electron-transfer proteins Electron-transfer reactions in photosynthesis involve electron carriers or electron-transfer proteins, including, among others, quinones, cytochromes, and iron-sulfur proteins. In the following, we present a summary of the carriers or associated proteins that are primarily involved in photosynthetic electron-transfer reactions, along with a listing in Fig. 20. Although ATP is not an electron carrier, it is included in the figure to remind us of the common components present in the structures of ATP and NAD(P) molecules [see Fig. 20 (A)]. 

Pathway analysis of protein electron-transfer reactions. 

Marcus theory has been used to interpret the reactions of cytochromes c and blue copper proteins. For thirteen protein-protein electron-transfer reactions, the data can be fitted with the self-exchange rate constants of 2.8 x 10 s ... 

Fig. 23. Coupling the cyclic voltammetry of horse cytochrome c (as promoted at a Au electrode in the presence of 4,4 -bipyridyl) to reduction of Oj by Pseudomonas aeruginosa cytochrome cd via a sequence of protein-protein electron-transfer reactions. Aerobic solutions contained 0.1 M NaC104, 0.02 M phosphate, pH 7.0. Scan rate 1 mVs . a) horse cytochrome c (0.44 mM) alone, b) after an addition, of cytochrome cd to 6 pM. c) after a further addition, of azurin to 0.25 pM. Redrawn from Ref. 198, with kind permission...

Table 18.6 lists formal potentials for common protein electron transfer reactions in biologically related systems. Table 18.7 lists standard reduction potentials for biochemical reduction reactions. 

The properties of electron transfer proteins that are discussed here specifically affect the electron transfer reaction and not the association or binding of the reactants. A brief overview of these properties is given here more detailed discussions may be found elsewhere (e.g.. Ref. 1). The process of electron transfer is a very simple chemical reaction, i.e., the transfer of an electron from the donor redox site to the acceptor redox site. 

The environmental (i.e., solvent and/or protein) free energy curves for electron transfer reactions can be generated from histograms of the polarization energies, as in the works of Warshel and coworkers [79,80]. 

The side chains of the 20 different amino acids listed in Panel 1.1 (pp. 6-7) have very different chemical properties and are utilized for a wide variety of biological functions. However, their chemical versatility is not unlimited, and for some functions metal atoms are more suitable and more efficient. Electron-transfer reactions are an important example. Fortunately the side chains of histidine, cysteine, aspartic acid, and glutamic acid are excellent metal ligands, and a fairly large number of proteins have recruited metal atoms as intrinsic parts of their structures among the frequently used metals are iron, zinc, magnesium, and calcium. Several metallo proteins are discussed in detail in later chapters and it suffices here to mention briefly a few examples of iron and zinc proteins. 

The most conspicuous use of iron in biological systems is in our blood, where the erythrocytes are filled with the oxygen-binding protein hemoglobin. The red color of blood is due to the iron atom bound to the heme group in hemoglobin. Similar heme-bound iron atoms are present in a number of proteins involved in electron-transfer reactions, notably cytochromes. A chemically more sophisticated use of iron is found in an enzyme, ribo nucleotide reductase, that catalyzes the conversion of ribonucleotides to deoxyribonucleotides, an important step in the synthesis of the building blocks of DNA. 

The bifurcation of the electron pathways is aided by the mobility of the catalytic domain of the Rieske protein. Three positional states of the catalytic domain of the Rieske protein have been observed in different crystal forms of the 6ci complex (Fig. 8b see Section III,B,5) (41, 42). In each single positional state, the Rieske protein is unable to perform all electron transfer reactions occuring during turnover ... 

Cluster 1 is a conventional [4Fe-4S] cubane cluster bound near the N-terminus of the molecule as shown in Fig. 13. Within the cluster the Fe-S bonds range from 2.26 to 2.39 A. The cluster is linked to the protein by four cysteine residues with Fe-S distances ranging from 2.21 to 2.35 A, but the distribution of the cysteine residues along the polypeptide chain contrasts markedly with that found, for example, in the ferredoxins as indicated in Section II,B,4 [also see, for example, 41) and references therein]. In the Fepr protein all four cysteine residues (Cys 3, 6, 15, and 21) originate from the N-terminus of the molecule, and the fold of the polypeptide chain in this region is such that it wraps itself tightly around the cluster, yet keeps it near the surface of the molecule. In such a position the cluster is ideally placed to participate in one-electron transfer reactions with other molecules. 

Cyclic voltammetry and other electrochemical methods offer important and sometimes unique approaches to the electroactive species. Protein organization and kinetic approaches (Correia dos Santos et al. 1999, Schlereth 1999) can also be studied by electrochemical survey. The electron transfer reaction between cytochrome P450scc is an important system for... 

Iron-sulfur proteins. In an iroinsulfiir protein, the metal center is surrounded by a group of sulfur donor atoms in a tetrahedral environment. Box 14-2 describes the roles that iron-sulfur proteins play in nitrogenase, and Figure 20-30 shows the structures about the metal in three different types of iron-sulfur redox centers. One type (Figure 20-30a l contains a single iron atom bound to four cysteine ligands. The electron transfer reactions at these centers... 

C20-0073. Draw a crystal field splitting diagram that illustrates the electron transfer reaction of the simple iron redox protein shown in Figure 20-29a. 

In this chapter, a novel interpretation of the membrane transport process elucidated based on a voltammetric concept and method is presented, and the important role of charge transfer reactions at aqueous-membrane interfaces in the membrane transport is emphasized [10,17,18]. Then, three respiration mimetic charge (ion or electron) transfer reactions observed by the present authors at the interface between an aqueous solution and an organic solution in the absence of any enzymes or proteins are introduced, and selective ion transfer reactions coupled with the electron transfer reactions are discussed [19-23]. The reaction processes of the charge transfer reactions and the energetic relations... 

Marcus, R., Electron transfer reactions in chemistry theory and experiment. In Protein Electron Transfer (1996), Bendall, D., Ed., BIOS Scientific Oxford, pp. 249-272... 

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