Resonance Raman optical activity and surface enhanced resonance Raman optical activity analysis of cytochrome c

High-resolution resonance Raman (RR) and resonance Raman optical activity (ROA) spectra of cytochrome c were obtained in order to perform full assignment of spectral features of the resonance ROA spectrum. The resonance ROA spectrum of cytochrome c revealed a distinct spectral signature pattern due to resonance enhanced skeletal porphyrin vibrations, more pronounced than any contribution from the protein backbone. Combining the intrinsic resonance properties of cytochrome c with the surface plasmon enhancement achieved with colloidal silver particles, the surface enhanced resonance Raman scattering (SERRS) and surface enhanced resonance ROA (SERROA) spectra of the protein were successfully obtained at concentrations as low as 1 microM. The assignments of spectral features were based on the information obtained from the RR and resonance ROA spectra. Excellent agreement between RR and SERRS spectra is reported, while some disparities were observed between the resonance ROA and SERROA spectra. These differences can be ascribed to perturbations of the physical properties of the protein upon adhesion to the surface of the silver colloids.