title: Room-temperature vibrational difference spectrum for S2QB-/S1QB of photosystem II determined by time-resolved Fourier transform infrared spectroscopy.
abstract: Time-resolved FTIR spectroscopy has been used to kinetically characterize the vibrational properties of intact photosystem II-enriched membrane samples undergoing the S1QB-to-S2QB- transition at room temperature. To optimize the experimental conditions for the FTIR measurements, oxygen polarographic and variable chlorophyll a fluorescence measurements were used to define the decay of S2 and QA-, respectively. The flash-induced S2QB-/S1QB difference spectra were measured at a temporal resolution of 4.44 s and a spectral resolution of 4 cm-1. An intense positive band is observed at 1480 cm-1 in the difference spectrum and shows a slow decay with a half time of approximately 13 s. Based on its decay kinetics and analogy to the infrared absorption of QA- of photosystem II and QB- in bacterial reaction centers, we conclude that the 1480 cm-1 band arises from QB- of PSII and tentatively assign it to the upsilon(CO) mode of the semiquinone anion QB-. The infrared spectral features attributed to the S1-to-S2 transition of the Mn cluster at room temperature show striking similarity to the S2/S1 difference spectrum measured at cryogenic temperatures (Noguchi, T., Ono, T.-A., and Inoue, Y. (1995) Biochim. Biophys. Acta 1228, 189-200).
authors.affiliation: Research School of Biological Sciences, Institute of Advanced Studies and Department of Chemistry, Faculty of Science, The Australian National University, Canberra, ACT.
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: G
authors.initials: G
authors.lastname: Fischer
authors.forename: T
authors.initials: T
authors.lastname: Wydrzynski
mesh_terms: D002736:Chloroplasts / Q000737:chemistry / Q000187:drug effects; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects; D007425:Intracellular Membranes / Q000737:chemistry / Q000187:drug effects; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D010971:Plastoquinone / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea; D013696:Temperature
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese; D004237:Diuron; D010971:Plastoquinone