Identification of Fourier transform infrared signals from the non-heme iron in photosystem II.
Fourier transfer infrared (FTIR) signals originating from a high-potential electron acceptor in PS II were studied by flash-induced FTIR difference spectroscopy. Redox titration of these signals using ferri-ferrocyanide mixtures showed midpoint potentials (Em) of 489 +/- 12 and 426 +/- 9 mV at pH 5.5 and 6.5, respectively, revealing a pH dependence of about -60 mV/pH unit. These Em values and pH dependence were in good agreement with those of the non-heme iron, so-called Q400, located between QA and QB. This indicates that the observed FTIR signals are due to changes in ligands of the non-heme iron and surrounding protein moieties induced on photoreduction from Fe3+ to Fe2+.
Solar Energy Research Group, Institute of Physical and Chemical Research (RIKEN), Saitama.
T
T
Noguchi
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Y
Inoue
D004579:Electron Transport; D005290:Ferric Compounds; D006418:Heme; D007501:Iron / Q000737:chemistry*; D008564:Membrane Potentials; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D011540:Prussian Blue Reaction; D017550:Spectroscopy, Fourier Transform Infrared; D017186:Titrimetry
D005290:Ferric Compounds; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D006418:Heme; D007501:Iron