Voltammetry of cytochrome

Yeh and Kuwana " were the first to report on the electrochemistry of cytochrome c at doped metal oxide semiconductor electrodes. A nearly reversible electrode reaction was indicated by the cyclic voltammetry and differential pulse voltammetry of cytochrome c at tin-doped indium oxide electrodes. Except for the calculated diffusion coefficient, all of the characteristics of the electrochemistry of cytochrome c at this electrode indicated that the electrode reaction was well-behaved. A value of 0.5 x 10" cmVs was determined for the diffusion coefficient which, like previously determined values at mercury, is lower than the value obtained by nonelectrochemical methods (i.e., 1.1 X 10 cm /s " " ). The electrochemical response of cytochrome c at tin oxide semiconductor electrodes was reported to be quasi-reversible, although no details were given. " ... 

There is considerable evidence that cytochrome C3 strongly adsorbs on mercury. Mercury drops from a DME formed in solutions containing cytochrome C3 do not coalesce for 30 minutes and electrocapillary curves are lowered. At the hanging mercury drop electrode cyclic voltammetry of cytochrome C3 from Desulfovibrio vulgaris, strain Hildenborough, and also from Desulfovibrio desulfuricans, strain Norway, gave further evidence of adsorption. Each sample exhibited a peak at ca. OV characteristic of adsorption, i.e., current was directly proportional to scan rate. Film transfer... 

The voltammetry of cytochrome c at the pyrolytic graphite edge showed a marked pH dependence [91]. Analysis of the reduction current measured at a rotating-disk electrode as a function of pH showed that this was virtually abolished under acid conditions. A plot of log(ima, — i/imax) against pH was linear (slope 1.5) between pH 4.2 and 7.0 and yielded an effective pK of 5.6. A similar set of measurements on the reduction of Fe(CN)g under conditions of low ionic... 

Attempts have been made to assign individual potential values obtained from voltammetry to specific heme groups. In one example, the bulk-solution voltammetry of cytochromes was compared to voltammetry of the proteins adsorbed at silver electrodes and the corresponding SERS potentiometric data [35]. Since the adsorbed-film voltammetry gave potentials very close to the bulk solution values, it was concluded that the proteins were adsorbed essentially in their native forms. The SERS potentials each corresponded more closely to the electrochemical... 

An earlier extensive study by Edmund Bowden had demonstrated the importance of using electrodes with hydrophilic surfaces in electrochemical studies of cytochrome c [46]. At that time the cyclic voltammetry of cytochrome c at gold was found to decay with time, but the response could be restored on cleaning the electrode in a soft hydrogen flame that rendered the snrface hydrophilic. It is now clear that the lack of stability was due to these samples being chromato-graphicaUy purified, lyophilized, and then stored at °C for later nse. This produced oligomeric forms of cytochrome c that fouled metal electrode surfaces. Metal surfaces are more active to adsorption of protein impnrities than tin oxide and indium oxide and more easily fouled by protein adsorption. 

Figure 3 (A) Cychc voltammetry of cytochrome c a tin doped indium oxide optically...

Figure 4 (A) DCVA and (B) cyclic voltammetry of cytochrome c at silver. [Cyt c] = 199 M, 0.05 M NajSO, electrode...

Figure 3.96 The effect of increasing time of exposure (as indicated) of a gold electrode once-modified with SSBipy to thiophenol on the cyclic voltammetry of horse heart cytochrome t (0.4mM). 20 mM sodium phosphate/0.1 M NaCI04 pH 7.0. Scan rate 20mVs l. From Hill...

The molecular interaction of cytochrome c and cardiolipin has been extensively studied. A mode of the interaction has been confirmed to be both electrostatic and hydrophobic, by using infrared spectroscopy (Choi and Swanson, 1995), fluorescence resonance energy transfer method (Rytdmaa and Kinnunen, 1994), protease digestion (de Jongh et al., 1995), cyclic voltammetry (Salamon and ToUin, 1997), deuterium and phosphorus NMR measurements (Spooner et al., 1993), and surface plasmon resonance spectroscopy (Salamon and Tollin, 1996). 

One of the first reports on the quasireversible electrochemistry of redox proteins appeared in 1977 when Eddowes and Hill demonstrated (10) cyclic voltammetry of horse heart cytochrome c at a gold electrode in the presence of 4,4 -bipyridyl (Bipy) in solution. In the voltammo-grams (Fig. 1), the peak-to-peak separations were close to 60 mV and the faradaic currents varied linearly with (scan rate), indicating a quasireversible one-electron transfer process controlled by linear diffusion of redox species to the electrode surface. The midpoint potential... 

The direct voltammetry and bioelectrocatalytic activity of cytochrom c. HRP immobilized onto niobium oxide (Nb2Os) mesoporous matrix at inidium-tin oxide (ITO) electrode was investigated [282,283],The electron transfer rate constant of cytochrom c is 0.28 s"1, reflective of the intrinsic electron transfer rate. In addition mesoporous niobium... 

The reduction potentials of the Dsm.baculatum cytochrome c3 (Mr 26,000) hemes were determined by cyclic voltammetry, and found to be as low as those of cytochrome c3 [72]. Based on the four values obtained (-210, -270, -325, -365 mV at pH 7.6) the authors proposed that the hemes are bis-histidinyl coordinated. The amino-acid sequence of the Dsm.baculatum cytochrome c3 (Mr 26,000) was compared to the sequences of several polyheme cytochromes, giving evidence that this cytochrome is distinct from cytochrome c3 (Mr 13,000) [73]. The sequence of the D. gigas cytochrome has also been determined [71]. The crystal structure of the Dsm. baculatum cytochrome c3 (Mr 26,000) was obtained at 2.16 A resolution [74], Preliminary X-ray studies have also been reported for the D.gigas cytochrome [75]. 

Figure 12. Adsorption study of cytochrome c at the hanging mercury drop electrode by cyclic voltammetry. Solution contained 0.01 M Tris-HCl buffer, pH 7.6, electrode...

Figure 18. (A) Cyclic voltammetry of purified cytochrome c at doped indium oxide optically transparent electrodes. Solution contained 73 /uiM cytochrome c, 0.21 M Tris, 0.24 M cacodylic acid, pH 7.0, 0.20 M ionic strength. Electrode area = 0.71 cm. Potential scan rates in mV/s are (a) 100 (b) 50 (c) 20 (d) 10 (e) 5.0 (f) 2.0. (B) Derivative cyclic voltabsorptometry of purified cytochrome c at a tin-doped indium oxide optically transparent electrode. Same conditions as described above. Circles are calculated derivative cyclic voltabsorptometric responses for 73 /iM cytochrome c, formal potential = 0.260 V, n = 1.0, diffusion coefficient of oxidized and reduced cytochrome c = 1.2 x 10 cm /s, difference molar absorptivity at 416 nm = 57,000 cm" formal heterogeneous electron transfer rate constant = 1.0 x 10 cm/s, and electrochemical transfer coefficient = 0.5. Adapted from Reference (126) with permission.

In a recent report, it was demonstrated that adsorption of 4,4 -bipyridine on platinum led to quasi-reversible rates of electron transfer with cytochrome c as evidenced by cyclic voltammetry. However, the concentration of 4,4 -bipyridine required to produce this electrochemical response was five times that which is required at gold electrodes. This difference was ascribed to the difference in the tendency of 4,4 -bipyridine to adsorb at gold and platinum electrodes. These results indicate that the use of 4,4 -bipyridine may be applicable to other solid electrodes as well for the study of cytochrome c electron transfer reactions. 

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