Novel Phenolic Inhibitors of Electron Transfer in Photosystem II

Effect of Photosystem II inhibitor K-15 on photochemical reactions of the isolated D1/D2 cytochrome b559 complex

“…A 50% inhibition was induced by 5 #M K-15 and the effect was maximal in the range 20 to 200 #M. Photooxidation of P680 in the presence of 0.1 mM silicomolybdate was also efficiently inhibited by K-15 (50% inhibition at 15 #M). The data are consistent with the idea put forward earlier (Klimov et al 1992) that the inhibitory effect of K-15 is based on facilitating a rapid recombination between Pheoand P680 + (or Z +) via its redox properties. The inhibitor can be useful for suppressing PS II reactions in isolated RCs of PS II which are resistant to all traditional inhibitors, like diuron, and probably functions by substituting for QA missing in the preparation.…”

“…Recently, a new group of highly efficient PS II inhibitors, derivatives of perfluoroisopropyldinitrobenzol, has been found and inhibitory effects of one of them, K-15 (4-[methoxy-bis-(trifluoromethyl)methyl]-2 6-dinitrophenyl hydrazone methyl ketone) studied in detail using PS II membrane fragments (Klimov et al 1992;Allakhverdiev et al 1989;Kisselev et al 1993;Zharmukhamedov et al 1994). Its effect (at submicromolar concentrations) on photoinduced changes of chlorophyll fluorescence yield (AF), oxygen evolution, photoreduction of Pheo, photooxidation of P6s0 (Klimov et al 1992) and chlorophyll fluorescence lifetimes (AUakhverdiev et al 1989) led to the conclusion that the inhibitory effect involves a redox interaction of K-15 with the components of reaction centres (RC).…”

“…Its effect (at submicromolar concentrations) on photoinduced changes of chlorophyll fluorescence yield (AF), oxygen evolution, photoreduction of Pheo, photooxidation of P6s0 (Klimov et al 1992) and chlorophyll fluorescence lifetimes (AUakhverdiev et al 1989) led to the conclusion that the inhibitory effect involves a redox interaction of K-15 with the components of reaction centres (RC). In so doing it was suggested that it caused a short circuit of electron transfer resulting in an acceleration of the charge recombination between the radical pairs P680 Pheo-or Z + Pheo- (Klimov et al 1992).…”

“…The value of the redox potential of the pair K-15/K-15-(-0.53 V) (Kisselev et al 1993) and the capability of K-15 to maintain an inhibitory action during long periods of illumination at a ratio of K-15:RC close to 1:1 (or lower) (Klimov et al 1992) are consistent with the idea that K-15 acts as a mediator for back electron transfer between Pheo-and P6s0 + (or Z + ). The high value of the binding constant of K-15 to PS II membrane fragments (Klimov et al 1992), the lack of competition between K-15 and diuron for the binding site (Zharmukhamedov et al 1994) as well as redox interaction of K-15 with Pheo-led to the suggestion that K-15 occupies the QA -binding site and serves as a substitute for QA (in contrast to diuron or atrazine which replace QB and are not redox active) (Klimov et al 1992;Zharmukhamedov et al 1994).…”

“…The high value of the binding constant of K-15 to PS II membrane fragments (Klimov et al 1992), the lack of competition between K-15 and diuron for the binding site (Zharmukhamedov et al 1994) as well as redox interaction of K-15 with Pheo-led to the suggestion that K-15 occupies the QA -binding site and serves as a substitute for QA (in contrast to diuron or atrazine which replace QB and are not redox active) (Klimov et al 1992;Zharmukhamedov et al 1994).…”