15] Resonance raman spectra of hemoproteins

Abstract

It is possible to use the resonance raman (RR) spectra to evaluate protein influences on heine structure. This chapter describes the RR spectra of hemoproteins. The heme group has strong absorption bands in the visible and nearultraviolet region, accessible to the argon ion laser (4579–5286 .A,) that is the common Raman light source. RR spectra, containing several vibrational modes of the heme group, are readily obtainable at concentrations of 10 –3 –10 –5 M, well below the concentrations at which normal polypeptide Raman bands can be observed. It is suggested that to use RR spectroscopy, it is important to understand—at least qualitatively—what sorts of enhancement patterns to expect and the appearance of the RR spectrum depends markedly on the laser wavelength. The vibrational symmetries can be determined by the polarizations of the Raman bands. The laser polarization is oriented perpendicular to the scattering direction. The scattered light can be analyzed into two components, with polarization parallel or perpendicular to the incident polarization. The resonant π–π transitions are polarized in the heine plane, and RR enhancement is expected for those vibrations which alter the in-plane polarizability.