title: Light-induced Fourier transform infrared spectrum of the cation radical P680+.
abstract: The structure of the primary electron donor of photosystem II, P680, is still under debate. It is not decided if it is composed of a chlorophyll (Chl) monomer or dimer. In this study, Fourier transform infrared (FTIR) spectroscopy was used to analyze the changes in the vibration modes occurring upon photooxidation of P680 in a Mn-depleted PS II preparation. It is demonstrated that illumination of the above in the presence of artificial electron acceptors results in a light-minus-dark absorbance change typical of the formation of P680+. The light-minus-dark difference FTIR spectrum obtained under similar conditions is characterized by two negative peaks located at 1694 and 1652 or 1626 cm-1 that can be assigned to the 9-keto groups of the P680 Chl, the latter band being indicative of a strongly associated group. These vibrations are shifted to 1714 and 1676 cm-1, respectively, in the positive features of the difference spectrum attributed to P680+. The occurrence of two pairs of bands attributed to 9-keto groups is discussed in terms of P680 being formed of a Chl dimer.
authors.affiliation: Centre de recherche en photobiophysique, Université du Québec à Trois-Rivières, Canada.
authors.forename: S I
authors.initials: SI
authors.lastname: Allakhverdiev
authors.forename: A
authors.initials: A
authors.lastname: Ahmed
authors.forename: H A
authors.initials: HA
authors.lastname: Tajmir-Riahi
authors.forename: V V
authors.initials: VV
authors.lastname: Klimov
authors.forename: R
authors.initials: R
authors.lastname: Carpentier
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D008027:Light; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008345:Manganese / Q000494:pharmacology; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D008345:Manganese; C025167:P-680