Electron transfer kinetics of cytochrome c probed by time-resolved surface-enhanced resonance Raman spectroscopy.
An improved setup including a measuring cell was designed for time-resolved surface-enhanced resonance Raman (SERR) spectroscopy. The cell is based on a rotating disk electrode (RDE) made from electrochemically roughened Ag. Cytochrome c (cc) adsorbed on a monolayer of mercaptoethanol is investigated with respect to heterogeneous electron transfer. Cyclic voltammograms and potential-dependent static SERR spectra indicate cc to be electroactive on the Ag electrode. The standard redox potential was found to be 234 mV. Time-resolved SERR spectra were then measured triggered by periodic potential pulses changing the protein between the oxidized and reduced state at a frequency of 10 Hz. Monoexponential functions obtained from the intensity of the band at 1361 cm-1 plotted versus time yielded the rate constants of heterogeneous electron transfer to be k(ox) = 46 +/- 7 s(-1) and k(red) = 84 +/- 20 s(-1). These relatively low rates are in line with the orientation of cc on the mercaptoethanol-modified Ag electrode. In this case the heme cleft pointed away from the surface thus hampering electron transfer.
Grosserueschkamp
Marc
M
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Friedrich
Marcel G
MG
Plum
Markus
M
Knoll
Wolfgang
W
Naumann
Renate L C
RL
D045304:Cytochromes c / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D004579:Electron Transport; D007700:Kinetics; D010084:Oxidation-Reduction; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods*
D045304:Cytochromes c