Properties of <TEX>$Cl^-$</TEX> Binding Site in Oxygen-Evolving Complex of Photosystem II Studied by FTIR Spectroscopy

Role of cl<TEX>$^{[-10]}$</TEX> in photosynthetic oxygen-evolving complex was studied by light-induced Fourier transform infrared (FTIR) spectroscopy. cl<TEX>$^{[-10]}$</TEX> depletion resulted in the suppression of amide I and amide II IR modes upon S<TEX>$_1$</TEX> to S<TEX>$_2$</TEX> transition. Br<TEX>$^{[-10]}$</TEX> , 1<TEX>$^{[-10]}$</TEX> and N0<TEX>$_3$</TEX><TEX>$^{[-10]}$</TEX> substituted FTIR difference spectra were very similar to that in cl<TEX>$^{[-10]}$</TEX> reconstitution. F<TEX>$^{[-10]}$</TEX> and <TEX>$CH_3$</TEX>COO<TEX>$^{[-10]}$</TEX> substituted spectra were largely distorted. We succeeded in detecting the structural change of N0<TEX>$_3$</TEX> <TEX>$^{[-10]}$</TEX> in the cl<TEX>$^{[-10]}$</TEX> site upon the S<TEX>$_1$</TEX> to S<TEX>$_2$</TEX> transition from <TEX>$^{14}$</TEX> N0<TEX>$_3$</TEX><TEX>$^{[-10]}$</TEX> /<TEX>$^{15}$</TEX> N0<TEX>$_3$</TEX><TEX>$^{[-10]}$</TEX> difference spectrum.