Derivatives of Hydroxyperfluoroisopropyldinitrobenzole Inhibit Electron Transfer in Photosystem II

We have revealed new highly efficient inhibitors of electron transfer in photosystem II (PSI) of plants
-hydroxyperfluoroisopropyldinitrobenzole derivatives, designated as K15 type inhibitors. Their inhi-
bitory effect is based on the redox interactions with PSII reaction centre (RC) components accompa-
nied by formation of a short cyclic electron transfer chain which leads to rapid recombination of sepa-
rated charge in PSI. This conclusion is supported by the following effects obtained upon treatment of
isolated chloroplasts of higher plants or PSII preparations with K15: (1) inhibition of the photoin-
duced changes in chlorophyll fluorescen ce yield (AF) related to photoreduction of the primary electron
acceptor Qa and photoinduced absorption changes (AA) related to photoaccumulation of the primary
electron donor Peso in its oxidized form Peso ; (2) acceleration of dark relaxation and the decrease of
the amplitude of AA and AF related to photoreduction of the intermediary electron acceptor pheophy-
tin and the decrease in the fluorescence yield when Qa was prereduced; (3) disappearan ce of all these
effects upon addition of dithionite (which reduces KI5 in the dark) accompanied by an accelerated
electron don ation to RC; (4) coincidence of the concentration dependen ces of the inhibition by these
compounds of both oxygen evolution and the above mentioned reactions related to electron transfer in
PSIL RC (he value of the inhibition constant K, was found to be equal to 45 nM for KI5).