[Paramagnetic centers and photochemical reactions of photosystem 2 subchloroplast fragments].

ESR signals of highly purified subchloroplast fragments containing the Photosystem 2 (PS 2) were obtained. Reversibility of the ESR II signal in darkness in the presence of dichlorophenolindophenol (DCPIP) was observed. Reduction of DCPIP with chloroplast fragments in the absence of exogenous donors takes place in light without simultaneous liberation of O2. Electron transfer may be blocked by the displacement of manganese with Mg2+ and Ba2+ bivalent cations. Cd2+ cations partially suppress the electron transfer catalysed by PS 2. The inhibiting effect of Cd2+ is removed in the presence of exogenous Mn2+ or hydroxylamine.