title: Oxidation of the two beta-carotene molecules in the photosystem II reaction center.
abstract: We present a spectroscopic characterization of the two nonequivalent beta-carotene molecules in the photosystem II reaction center. Their electronic and vibrational properties exhibit significant differences, reflecting a somewhat different configuration for these two cofactors. Both carotenoid molecules are redox-active and can be oxidized by illumination of the reaction centers in the presence of an electron acceptor. The radical cation species show similar differences in their spectroscopic properties. The results are discussed in terms of the structure and unusual function of these carotenoids. In addition, the attribution of resonance Raman spectra of photosystem II preparations excited in the range 800-900 nm is discussed. Although contributions of chlorophyll cations cannot be formally ruled out, our results demonstrate that these spectra mainly arise from the cation radical species of the two carotenoids present in photosystem II reaction centers.
authors.affiliation: Wolfson Laboratories, Department of Biological Sciences, Imperial College of Science, Technology and Medicine, London SW7 2AY, UK.
authors.forename: Alison
authors.initials: A
authors.lastname: Telfer
authors.forename: Dmitrij
authors.initials: D
authors.lastname: Frolov
authors.forename: James
authors.initials: J
authors.lastname: Barber
authors.forename: Bruno
authors.initials: B
authors.lastname: Robert
authors.forename: Andy
authors.initials: A
authors.lastname: Pascal
mesh_terms: D002412:Cations / Q000737:chemistry / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D003080:Cold Temperature; D005615:Freezing; D007834:Lasers; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008982:Molybdenum / Q000737:chemistry; D010084:Oxidation-Reduction; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D017655:Silicon Compounds / Q000737:chemistry; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D018724:Spinacia oleracea; D019207:beta Carotene / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002412:Cations; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D017655:Silicon Compounds; D019207:beta Carotene; C013250:silicomolybdate; D002734:Chlorophyll; C025167:P-680; D008982:Molybdenum