Primary donor structure and interactions in bacterial reaction centers from near-infrared Fourier transform resonance Raman spectroscopy.
Preresonance Raman and resonance Raman spectra of the primary donor (P) from reaction centers of the Rhodobacter (Rb.) sphaeroides R26 carotenoidless strain in the P and P+ states, respectively, were obtained at room temperature with 1064-nm excitation and a Fourier transform spectrometer. These spectra clearly indicate that the chromophore modes are observable over those of the protein with no signs of interference below 1800 cm-1. The chromophore modes are dominated by those of the bacteriochlorophylls (BChl a), and it is estimated that, in the P state, ca. 65% of the Raman intensity of the BChl a modes arises from the primary donor. This permits the direct observation of a vibrational spectrum of the primary donor at preresonance with the excitonic 865-nm band. The Raman spectrum of oxidized reaction centers in the presence of ferricyanide clearly exhibits bands arising from a BChl a+ species. The magnitude of the frequency shift of a keto carbonyl of neutral P from 1691 to 1717 cm-1 upon P+ formation strongly suggests that one BChl molecule in P+ carries nearly the full +1 charge. Our results indicate that the unpaired electron in P.+ does not share a molecular orbital common to the two components of the dimer on the time scale of the resonance Raman effect (ca. 10(-13) s).
Mattioli
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TA
Département de Biologie Cellulaire et Moléculaire, Centre d'Etudes de Saclay, Gif-sur-Yvette, France.
Hoffmann
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A
Robert
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Schrader
B
B
Lutz
M
M
D005583:Fourier Analysis; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D012242:Rhodobacter sphaeroides / Q000378:metabolism; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
D045322:Photosynthetic Reaction Center Complex Proteins