Interfacial Redox Processes of Cytochrome b562 (hot article)

ZHUO, P.; ALBRECHT, T.; BARRER, P.D.; MURGIDA, D.H.; HILDEBRANDT, P.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2009 vol. 34 p. 7430 - 7436

1463-9076

The anionic soluble heme protein cytochrome b562 was electrostatically immobilised on Agelectrodes coated with positively charged self-assembled monolayers of amino-terminatedalkanethiols. The structure of the heme pocket, the redox equilibria, and the electron transferdynamics were studied by stationary and time-resolved surface enhanced resonance Ramanspectroscopy, complemented by cyclic voltammetry measurements of the interfacial redox process.The conformational and redox equilibria of the immobilised protein are compared to those of thecationic heme protein cytochrome c immobilised on negatively charged electrode coatings.Similarities and differences can be rationalised in terms of the respective electric fields at theinterfaces of amino- and carboxyl-terminated electrode coatings. The heterogeneous electrontransfer rate of cytochrome b562 only slightly increases with decreasing thickness from ca. 20 to11 A ˚ , implying that the electron tunneling is not the rate-limiting step. In contrast to cytochromec on carboxyl-terminated monolayers, this behaviour cannot be attributed to proteinre-orientation gating the heterogeneous electron transfer. Instead, it may reflect the interplaybetween interprotein electron transfer and heterogeneous electron transfer via protein orientationsexhibiting particularly high tunneling probabilities for the electron exchange with the electrode.