Fourier Transform Raman Spectroscopy of Photoactive Proteins with Near-Infrared Excitation

Abstract

The Fourier transform (FT) Raman spectroscopic treatment of the photoactive proteins bacteriorhodopsin and the photosynthetic reaction center is reported, with excitation at 1.06 µm. Excitation at this wavelength circumvents the limitations on resonance Raman spectroscopy of these proteins imposed by their photolability and by the fluorescence of free pigments or impurities. The spectra are dominated by nonresonant Raman scattering by the protein-bound pigments retinal (in bacteriorhodopsin) and bacteriopheophytin, bacteriochlorophyll, and carotenoids (in reaction centers). The relative intensities of retinylidene modes in the spectrum for nonresonant FT Raman spectroscopy of bacteriorhodopsin are nearly identical to those observed in the resonance Raman spectrum of bacteriorhodopsin.