title: Bicarbonate binding to the water-oxidizing complex in the photosystem II. A Fourier transform infrared spectroscopy study.
abstract: The light-induced Fourier transform infrared difference (FT-IR) spectrum originating from the donor side of O2-evolving photosystem (PS) II was obtained in non-depleted and CO2-depleted PSII membrane preparations. The observed spectrum free of contributions from the acceptor side signals was achieved by employing 2 mM/18 mM ferri-/ferrocyanide as a redox couple. This spectrum showed main positive bands at 1589 and 1365 cm(-1) and negative bands at 1560, 1541, 1522 and 1507 cm(-1). CO-depleted PSII preparations showed a quite different spectrum. The main positive and negative bands disappeared after depletion of bicarbonate. The addition of bicarbonate partially restored those bands again. Comparison between difference FT-IR spectra of untreated and bicarbonate-depleted PSII membranes indicated that the positive bands at 1589 and 1365 cm(-1) can be assigned to COO- stretching modes from bicarbonate. The higher frequency corresponds to u[as] (COO-) and the lower frequency to u[s] (COO-). 13C-Labeling FT-IR measurements confirmed these findings and also suggested that the negative band at 1560 cm(-1) can be ascribed to u[as] (COO-). The data are discussed in the framework of the suggestion that bicarbonate can be a ligand to the Mn-containing water-oxidizing complex of PSII.
authors.affiliation: Estación Experimental Aula Dei, Consejo Superior de Investigaciones Científicas, Zaragoza, Spain. yruela@eead.csic.es
authors.forename: I
authors.initials: I
authors.lastname: Yruela
authors.forename: S I
authors.initials: SI
authors.lastname: Allakhverdiev
authors.forename: J V
authors.initials: JV
authors.lastname: Ibarra
authors.forename: V V
authors.initials: VV
authors.lastname: Klimov
mesh_terms: D001639:Bicarbonates / Q000378:metabolism*; D005292:Ferricyanides / Q000378:metabolism; D005295:Ferrocyanides / Q000378:metabolism; D008027:Light; D008345:Manganese / Q000378:metabolism; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism; D011485:Protein Binding; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea / Q000737:chemistry; D014867:Water / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D005292:Ferricyanides; D005295:Ferrocyanides; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D014867:Water; C007931:hexacyanoferrate III; D008345:Manganese; C020354:hexacyanoferrate II