Cytochrome interface

In the pursuit of mechanisms for electron transfer, various cytochromes and enzymes have been isolated and purified. A list of proteins implicated in the electron transfer processes with reduction of electron acceptor is given in Table 16.5. Although reductases have considerable specificity for reduction, it is apparent that the low-potential multiheme cytochromes interface with numerous different electron acceptors. 

G. Wang, J.J. Xu, and H.Y. Chen, Interfacing cytochrome c to electrodes with a DNA-carbon nanotube composite film. Electrochem. Commun. 4, 506-509 (2002). 

In the experiment, ZnCcP is produced by laser photolysis, then transient absorption spectroscopy follows the formation (k ) and decay (/Ceb) of ZnCcP + in wild-type and mutant crystals. Kang and Crane have studied the effects of interface mutations on electron transfer rates in single crystals using complexes between a zinc-substituted cytochrome c peroxidase (ZnCcP) and site-directed mutants of yeast cytochrome c (yCc).The mutants replaced the... 

Dungan et al. [186] have measured the interfacial mass transfer coefficients for the transfer of proteins (a-chymotrypsin and cytochrome C) between a bulk aqueous phase and a reverse micellar phase using a stirred diffusion cell and showed that charge interactions play a dominant role in the interfacial forward transport kinetics. The flux of protein across the bulk interface separating an aqueous buffered solution and a reverse micellar phase was measured for the purpose. Kinetic parameters for the transfer of proteins to or from a reverse micellar solution were determined at a given salt concentration, pH, and stirring... 

Tween 85 is used extensively for RME [84]. Russell and coworkers [234] used Tween 85/isopropanol microemulsions in hexane to solubilize proteins and not only showed >80% solubilization of cytochrome C at optimum conditions, but also proved that Tween 85 does not have a detrimental effect on the structure, function, and stability of subtilisin and cytochrome C. There are other reports available on the extraction and purification of proteins using Tween 85-RMs and also on the stability of protein activity in these systems [234]. It has also been shown that Tween 85-RMs can solubilize larger amounts of protein and water than AOT. Tween 85 has an HLB of 11, which indicates that it is soluble in organic solvents. In addition, it is biodegradable and can be successfully used as an additive in fertihzers [235,236]. Pfammatter et al. [35] have demonstrated that RMs made of Tween 85 and Span 80 can be successfully used for the solubilization and growth of whole cells. Recently, Hossain et al. [84] showed an enhanced enzymatic activity of Chromobacterium viscosum Hpase in AOT/Tween 85 mixed reverse micellar systems when compared to that in classical AOT-RMs. This is due to the modification of the interface in AOT-RMs caused by the co-adsorption of Tween 85, and increased availability of the oHve oil molecules (substrate) to the enzyme. 

The principal function of cyt. c is to form complexes through a defined interface with protein partners in our cells. This is most established for eukaryotic cytochrome c within the mitochondrial electron transport chain (ETC), a process required for carrying out the oxidative phosphorylation of ATP.4 Formation of a complex with cyt. c reductase (an electron-donor protein from complex III) and cyt. c oxidase (an electron-acceptor protein from complex IV) leads to the transfer of electrons between otherwise separated proteins. More recently cyt. c has been found to play a critical role in the process of apoptosis or programmed cell death This in turn has led to a resurgence of interest in all aspects of cyt. c research.5 Again protein-protein interactions have been shown be essential with mitochrondrial cyt. c binding to such proteins as APAF-1 to form the multi-protein species known as the apoptosome that is now thought to be a requirement for apoptosis.6,7... 

Figure 1. (a) X-ray crystal structure of horse-heart ferricytochrome c.8 All protein atoms are shown in the C.-P.-K. form, while the heme group is shown in the stick form. All Arg and Lys residues are colored blue, while Glu and Asp are colored in red, to contrast the destribution of the most ionizable side chains, (b) The X-ray crystal structure of horse heart ferricytochrome c in complex with horse cytochrome c peroxidase (cep).9 The peroxidase is shown as a molecular surface model, with blue regions depicting positive and red representing negative electrostatic potential. Note the cluster of negative potential on ccp that surrounds the contact interface. 

The construction of an artificial protein-protein complex is an attractive subject to elucidate the electron-transfer process in biological systems. To convert Mb into an electron-transfer protein such as cytochromes, Hayashi and Ogoshi (101) prepared a new zinc Mb having a unique interface on the protein surface by the reconstitutional method as shown in Fig. 27. The modified zinc protoporphyrin has multiple functional groups, carboxylates, or ammonium groups, at the terminal of the two propionates. Thus, the incorporation of the... 

Scheme 10 Reversible photoswitchable activation/deactivation of the electrical contact between cytochrome c and the electrode and the secondary activation/deactivation of the COx-biocata-lyzed reduction of oxygen using a thiolated nitrospiropyran and thiolated pyridine mixed monolayer as a command interface.

For benzene hydroxylation an analytical system [37] was successfully used at the interface. This system contains Fe3+ hydrophobic complexes, which promote the process intensification. It is shown [38, 39] that compared with hydrophobic complexes, Fe3+ complexes with the phase transfer—tertiary ammonium salts and crown ethers—display more effective action. At 20-50 °C, owing to the use of trimethylacetylammonium bromide as the phase transferring agent, benzene is successfully hydroxylated in the two-phase water-benzene system in the presence of Fe3+ ions [40], Hence, it is Shilov s opinion [41] that in the case of cytochrome P-450 a radical reaction is probable. It produces radicals, which then transform in the cell, as follows ... 

Fig. 14.36. Structure of horse cytochrome c obtained from the Brookhaven Protein Data Bank. Shown is the conventional front face view highlighting the exposed edge of the heme group (dark gray) located in a region of positive surface charge resulting from several lysine residues. (Reprinted from E. Bowden, Wiring Mother Nature, Interface 6(4) 40—45, Fig. 1, 1997. Reproduced by permission of the Electrochemical Society, Inc.)...

It has been pointed out that cytochrome c with its MW of 12,500 is enormous in size compared with the usual entities undergoing electron transfer at interfaces, which have molecular weights of about 100. However, Armstrong et al. (1996) took... 

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