title: A time-resolved FTIR difference study of the plastoquinone QA and redox-active tyrosine YZ interactions in photosystem II.
abstract: In this paper, we present the first time-dependent measurements of flash-induced infrared difference spectra of photosystem II (PSII) using Fourier transform infrared (FTIR) spectroscopy. With this experimental approach, we were able to obtain the YZoxQA-/YZQA vibrational difference spectrum of Tris-washed, PSII-enriched samples in the absence of hydroxylamine at room temperature (16 +/- 2 degrees C), with a spectral resolution of 4 cm-1 and a temporal resolution of 50 ms. In order to determine the dominant species in the FTIR spectrum at a particular point in time after an excitation flash, the decay kinetics of YZox and QA- were independently monitored by EPR and chlorophyll a fluorescence, respectively, under the same experimental conditions. These measurements confirmed that the addition of DCMU to Tris-washed PSII samples does not significantly affect the YZox decay, but does substantially slow down the QA- decay. By making use of the difference in the decay kinetics using DCMU, the QA-/QA signals could be separated from the YZox/YZ signals and a pure QA-/QA difference spectrum obtained. By comparison of the YZoxQA-/YZQA difference spectrum with the pure QA-/QA difference spectrum, a large differential band at 1706/1699 cm-1 could be identified and associated with YZ oxidation. In contrast, an intense band at 1478 cm-1, whose DCMU-sensitive decay follows the QA- decay based on the chlorophyll a fluorescence measurements, was present in all of the time-resolved spectra. Since no significant reversible Chl+ radicals could be detected by the EPR measurements under our experimental conditions, we confirm that this band most likely arises only from the semiquinone anion QA- [Berthomieu, C., Nabedryk, E., Mäntele, W., & Breton, J. (1990) FEBS Lett. 269, 363-367].
authors.affiliation: Research School of Biological Sciences, Institute of Advanced Studies, The Australian National University, Canberra, Australia 0200.
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: M R
authors.initials: MR
authors.lastname: Razeghifard
authors.forename: G
authors.initials: G
authors.lastname: Fischer
authors.forename: T
authors.initials: T
authors.lastname: Wydrzynski
mesh_terms: D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010971:Plastoquinone / Q000737:chemistry* / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C025232:semiquinone radicals; D014443:Tyrosine; D010971:Plastoquinone; D000077194:Chlorophyll A