Direct electron transfer of cytochrome

Reviews have appeared on the spectroelectrochemistry of biological molecules [104, 233]. Specialized reviews are also available on the direct electron transfer of cytochrome c [234] and potential inorganic redox reagents as mediators [235]. 

Shumyantseva VV, Ivanov YD, Bistolas N, Scheller EW, Archakov AI, Wollenberger U (2004) Direct electron transfer of cytochrome P450 2B4 at electrodes modified with nonionic detergent and colloidal clay nanoparticles. Anal Chem 76 6046-6052... 

Wu, J.-F., M.-Q. Xu, and G.-C. Zhao. 2010. Graphene-based modified electrode for the direct electron transfer of cytochrome c and biosensing. Electrochem. Commun. 12 175-177. 

Figure 1. Schematic representation of various surfaces so far developed at which rapid direct electron-transfer of cytochrome c can take place.

Biosensors based on direct electron transfer of proteins cytochrome c... 

Gold nanoparticles have been used to immobilize micro-peroxidase 11,46 tyrosinase,47 and hemoglobin48 to construct amperometric sensors, while silver nanoparticles have been used to enhance electron transfer of cytochrome c and myoglobin onto pyrolitic graphite electrodes.49 The use of semiconductor and oxide nanoparticles has also been reported, such as horseradish peroxidase (HRP) on TiC>2 nanoparticles,50 as well as Fe304 and MnC>4 nanoparticles to immobilize and facilitate direct electron transfer.51... 

The present view is that cytochrome a is the acceptor of electrons from cytochrome c, but that a simple linear electron-transfer sequence from cytochrome a to Cua and then to the cytochrome 03/Cub centre is unlikely. Instead the sequence shown in equation (63) holds, where cytochrome a is in rapid equilibrium with Cua. These views depend largely upon pre-steady-state kinetics of the redox half reactions of the enzyme with its two substrates, ferrocytochrome c and O2. However, these conclusions are not in accord with kinetic studies under conditions when both substrates are bound to the enzyme, and which show maximal rates of electron transfer from cytochrome c to O2. In particular some of the cytochrome c is oxidized at a faster rate than a metal centre in the oxidase. In contrast, at high ionic strength conditions, where the cytochrome c and the cytochrome oxidase are mainly dissociated, oxidation of cytochrome c occurs only slowly following the complete oxidation of the oxidase. These results for the fast oxidation of cytochrome c have been interpreted in terms of direct electron transfer from cytochrome c to the bridged peroxo intermediate involving 03 and Cub, or to a two-electron transfer to O2 from cytochromes a and 03 during the initial phase of the reaction. 

The stepwise transfer of electrons from cytochrome c to cytochrome via cytochrome a is kinetically favorable due to a substantial decrease in the medium reorganization energy for direct electron transfer from cytochrome c to cytochrome a. The redox potential of FOc may not be smaller, but even greater than the redox potential of FOg. It is essential that only the minimum of the intermediate term on the reaction energy diagram be below the cross-point of the initial and final terms. 

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