title: An EPR study of the pH dependence of formate effects on Photosystem II.
abstract: Effects of formate on rates of O(2) evolution and electron paramagnetic resonance (EPR) signals were observed in the oxygen evolving PS II membranes as a function of pH. In formate treated PS II membranes, decrease in pH value resulted in the inhibition of the O(2) evolving activity, a decrease in the intensity of S(2) state multiline signal but an increase in the intensity of the Q(A)(-)Fe(2+) EPR signal. Time-resolved EPR study of the Y(Z)(*) decay kinetics showed that the light-induced intensity of Y(Z)(*) EPR signal was proportional to the formate concentration. The change in the pH affected both the light-induced intensities and the decay rates of Y(Z)(*), which was found to be faster at lower pH. At 253 K, t(1/e) value of Y(Z)(*) decay kinetics was found to be 8-10 s at pH 6.0 and 18-21 s at pH 5.0. The results presented here indicate that the extent of inhibition at the donor and the acceptor side of PS II due to formate is pH dependent, being more effective at lower pH.
authors.affiliation: School of Life Sciences, Devi Ahilya Vishwavidyalaya, Indore 452 017, India. anjanajajoo@hotmail.com
authors.forename: Anjana
authors.initials: A
authors.lastname: Jajoo
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Katsuta
authors.forename: Asako
authors.initials: A
authors.lastname: Kawamori
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005561:Formates / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007501:Iron; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000187:drug effects* / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D005561:Formates; D045332:Photosystem II Protein Complex; C030544:formic acid; D007501:Iron; D010100:Oxygen