title: A thermal broadening analysis of absorption spectra of the D1/D2/cytochrome b-559 complex in terms of Gaussian decomposition sub-bands.
abstract: Absorption spectra of the isolated D1/D2/cytochrome b-559 complex have been measured in the temperature range 80-300 K. All spectra were analyzed in terms of a linear combination of Gaussian bands and the thermal broadening data interpreted in terms of a model in which the spectrum of each pigment site is broadened by (a) a homogeneous component due to linear electron-phonon coupling to a low-frequency protein vibration and (b) an inhomogeneous component associated with stochastic fluctuations at each pigment site. In order to obtain a numerically adequate description of the absorption spectra, a minimum number of five sub-bands is required. Further refinement of this sub-band description was achieved by taking into account published data from hole burning and absorption difference spectroscopy. In this way, both a six sub-band description and a seven sub-band description were generated. In arriving at the seven sub-band description, the original five sub-band wavelength positions were essentially unchanged. Thermal broadening analysis of the seven sub-band description yielded data which displayed the closest correspondence with the literature observations. The wavelength positions of the sub-bands were near 661, 667, 670, and 675 nm, with two bands near 680 and 684 nm. The two almost isoenergetic sub-bands near 680 nm, identified as P680 and pheophytin, have optical reorganization energies around 40 and 16 cm-1, respectively. All other sub-bands, identified as accessory pigments, have optical reorganization energies close to 16 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Dipartimento di Biologia, Università di Milano, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Cattaneo
authors.forename: G
authors.initials: G
authors.lastname: Zucchelli
authors.forename: F M
authors.initials: FM
authors.lastname: Garlaschi
authors.forename: L
authors.initials: L
authors.lastname: Finzi
authors.forename: R C
authors.initials: RC
authors.lastname: Jennings
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002736:Chloroplasts / Q000737:chemistry; D003573:Cytochrome b Group / Q000737:chemistry*; D006358:Hot Temperature; D045342:Light-Harvesting Protein Complexes; D008433:Mathematics; D010674:Pheophytins / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry; D045332:Photosystem II Protein Complex; D013053:Spectrophotometry; D003313:Zea mays
chemical_list: D003573:Cytochrome b Group; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C019313:cytochrome b559