Identification of Fourier Transform Infrared Signals from the Non-Heme Iron in Photosystem II

抄録

Fourier transfer infrared (FTIR) signals originating from a high-potential electron accep-tor in PS II were studied by flash-induced FTIR difference spectroscopy. Redox titration of these signals using ferri-ferrocyanide mixtures showed midpoint potentials (E_m) of 489±12 and 426±9mV at pH 5.5 and 6.5, respectively, revealing a pH dependence of about -60mV/pH unit. These E_m, values and pH dependence were in good agreement with those of the non-heme iron, so-called Q₄₀₀, located between Q_A and Q_B. 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 F²⁺.