VIBRATIONAL STUDIES OF ENERGY TRANSDUCING PROTEINS

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The specific aim of the proposed research is to characterize the structural and electronic properties of the active pigments in energy transducing proteins. The bacterial photosynthetic reaction center (RC) has been chosen for study because this class of proteins represents a prototypical model system for investigating the properties which facilitate fast electron transfer over distances on the order of the width of the biological membrane. In addition, the RC is the only integral membrane electron-transfer protein for which the macromolecular arrangement of the active pigments in the protein matrix is known. The principal investigative tool which will be used is resonance Raman (RR) spectroscopy, although infrared and electronic absorption spectroscopy will also play an important role. Semiempirical quantum force field and norma coordinate calculations will be used for the analysis of the spectroscopic data. The first objective is to characterize the vibrational and electronic properties of a series of model compounds. RR spectra will be acquired at a large number of excitation wavelengths which range from the ultraviolet to the red region of the absorption spectrum. The vibrational spectra will be assigned and descriptions will be obtained for the normal modes. Excitation profiles will be constructed for the resonance-enhanced Raman bands and the scattering mechanisms will be determined. The second objective is to characterize the vibrational and electronic properties of the active pigments in RCs. RR spectra will be obtained with excitation into a number of the absorption bands of the chromophores, including the photophysically-important near-infrared bands. The vibrational spectra will be assigned through comparison with those of the model compounds and the influence of the protein matrix on the structural and electronic properties of the pigments will be assessed. The third objective is to obtain RR spectra of genetically modified RCs in order to determine how specific protein residues affect the individual pigments. Collectively, the studies are intended to provide a more comprehensive picture of the relationship between the physical and function properties of the active pigments of energy transducing proteins in general.