Comprehensive resonance Raman study of photosynthetic reaction centers from Rhodobacter sphaeroides. Implications for pigment structure and pigment-protein interactions

• Published in: Journal of the American Chemical Society 1993-12, Vol.115 (25), p.12035-12049
• Main Authors: Palaniappan, Vaithianathan, Martin, Paul C, Chynwat, Veeradej, Frank, Harry A, Bocian, David F
• Format: Article
• Language: English
• Subjects: 140505 - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); 400102 - Chemical & Spectral Procedures; 400500 - Photochemistry; BACTERIA; Biological and medical sciences; CARBOXYLIC ACIDS; CHLOROPHYLL; CHLOROPHYLL-BINDING PROTEINS; DATA; ENERGY LEVELS; EXCITED STATES; EXPERIMENTAL DATA; Fundamental and applied biological sciences. Psychology; HETEROCYCLIC ACIDS; HETEROCYCLIC COMPOUNDS; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LASER SPECTROSCOPY; MICROORGANISMS; Molecular biophysics; NUMERICAL DATA; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; Photochemistry. Photosynthesis. Bioluminescence; PHOTOSYNTHETIC BACTERIA; PHOTOSYNTHETIC REACTION CENTERS; PHYTOCHROMES; PIGMENTS; PORPHYRINS; PROTEINS; Radiation-biomolecule interaction; RAMAN SPECTROSCOPY; Rhodobacter sphaeroides; SOLAR ENERGY; SPECTROSCOPY; THEORETICAL DATA; VIBRATIONAL STATES
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00078a048

Resonance Raman (RR) spectra are reported for photosynthetic reaction centers (RC's) from the purple bacterium Rhodobacter sphaeroides. The spectra of quinone-reduced RC's were obtained by using a large number of excitation wavelengths (23) in the 335-875-nm range. These wavelengths span the B sub(x), B sub(y), Q sub(x), and Q sub(y) absorption bands of the special pair bacteriochlorophyll (P), accessory bacteriochlorophyll (BCh), and bacteriopheophytin (BPh) pigments. The number of exciting lines and their wavelengths were chosen to optimize the selective excitation of the different pigments in the RC and to elicit the full complement of RR scattering from the individual pigments. The RR spectra of the quinone-reduced RC's were compared with one another and with those of chemically oxidized RC's, tetrapyrrolic model compounds, and BCh/BPh in solution. On the basis of these comparisons, a self-consistent set of vibrational assignments is proposed for the high-frequency (1425-1750/cm) carbonyl and skeletal modes of the six bacteriochlorin pigments in the protein. These assignments were aided by the results of semiempirical normal coordinate calculations. Collectively, the vibrational data and assignments indicate the following: (1) A reasonable set of vibrational assignments can be obtained. These assignments show that previous assignments for certain high-frequency modes and the interpretation of oxidation-induced frequency shifts observed in both static and time-resolved vibrational spectra must be reconsidered. (2) The structures of the L- and M-side accessory BCh's are essentially identical and similar to those of 5-coordinate BCh in solution. (3) The structures of the BCh's in P do not appear to be identical. The structure of one pigment of P is similar to that of the accessory BCh's. The vibrational frequencies of the other are consistent with either an expanded macrocycle core or a more conformationally distorted ring. (4) The structures of the L- and M-side BPh's are for the most part alike and similar to those of BPh in solution. However, the structure of BPh sub(L) in the region of rings III and V is different from that of BPh sub(M). This difference is due to the interaction of the C sub(9)-keto group of BPh sub(L) with the Glu sub(L104) residue. An equivalent pigment-protein interaction is absent on the M-side.