title: Ca(2+) function in photosynthetic oxygen evolution studied by alkali metal cations substitution.
abstract: Effects of adding monovalent alkali metal cations to Ca(2+)-depleted photosystem (PS)II membranes on the biochemical and spectroscopic properties of the oxygen-evolving complex were studied. The Ca(2+)-dependent oxygen evolution was competitively inhibited by K(+), Rb(+), and Cs(+), the ionic radii of which are larger than the radius of Ca(2+) but not inhibited significantly by Li(+) and Na(+), the ionic radii of which are smaller than that of Ca(2+). Ca(2+)-depleted membranes without metal cation supplementation showed normal S(2) multiline electron paramagnetic resonance (EPR) signal and an S(2)Q(A)(-) thermoluminescence (TL) band with a normal peak temperature after illumination under conditions for single turnover of PSII. Membranes supplemented with Li(+) or Na(+) showed properties similar to those of the Ca(2+)-depleted membranes, except for a small difference in the TL peak temperatures. The peak temperature of the TL band of membranes supplemented with K(+), Rb(+), or Cs(+) was elevated to approximately 38 degrees C which coincided with that of Y(D)(+)Q(A)(-) TL band, and no S(2) EPR signals were detected. The K(+)-induced high-temperature TL band and the S(2)Q(A)(-) TL band were interconvertible by the addition of K(+) or Ca(2+) in the dark. Both the Ca(2+)-depleted and the K(+)-substituted membranes showed the narrow EPR signal corresponding to the S(2)Y(Z)(+) state at g = 2 by illuminating the membranes under multiple turnover conditions. These results indicate that the ionic radii of the cations occupying Ca(2+)-binding site crucially affect the properties of the manganese cluster.
authors.affiliation: Laboratory for Photo-Biology, RIKEN Photodynamics Research Center, The Institute of Physical and Chemical Research, Aoba, Aramaki, Sendai 980-0845, Japan. takaaki@postman.riken.go.jp
authors.forename: T
authors.initials: T
authors.lastname: Ono
authors.forename: A
authors.initials: A
authors.lastname: Rompel
authors.forename: H
authors.initials: H
authors.lastname: Mino
authors.forename: N
authors.initials: N
authors.lastname: Chiba
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002412:Cations / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D049449:Luminescence; D008345:Manganese / Q000378:metabolism*; D008672:Metals, Alkali / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects; D010088:Oxidoreductases / Q000187:drug effects / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045332:Photosystem II Protein Complex; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D018724:Spinacia oleracea
chemical_list: D002412:Cations; D008672:Metals, Alkali; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese; D010088:Oxidoreductases; D011188:Potassium; D010100:Oxygen; D002118:Calcium