Resonance Raman scattering and surface-enhanced resonance Raman scattering studies of oxide-reduction of cytochrome c(3)

The tetraheme protein, cytochrome c(3) (cyt-c(3)), isolated from the sulfate-reducing bacterium, Desulfovibrio desulfuricans, strain NCIMB 8372, was examined with the resonance Raman scattering(RRS) and surface-enhanced resonance Raman scattering (SERRS) techniques. A comparison of the protein in solution and at a citrate-reduced silver sol shows the native structure of cyt-c(3) is retained at a SERRS-active substrate. No indication of high-spin states of adsorbed cyt-c(3) was observed. RRS and SERRS spectra were also acquired at intermediate redox states. Splitting of redox-state marker bands was observed and its relation to heme-heme interaction is discussed. In addition, SERRS spectra were acquired at an electrochemically-roughened SERRS-active substrate as a function of potential. The results suggest that the cytochrome is adsorbed to the Ag surface in an ordered fashion, with the heme exhibiting the most positive redox potential being closest to the surface.