A New-Type Photosystem II Inhibitor which Blocks Electron Transport in Water-Oxidation System

Abstract The mode of action of three types of conjugated enamine compounds was investigated by means of thermoluminescence measurement. Cyanoacrylate and 2-(l-ethoxyethylam inom ethylidene)- 4-dodecyl-5,5-dim ethyl-cyclohexane-1,3-dione (ACm12) converted the B-band (30 °C) arising from S 2 Q B - charge recombination to a downshifted 6 °C-band. This band was proved to be identical with the DCM U-induced Q-band (6 °C) arising from S 2 Q A - recombination, indicating that these two compounds block Q A to Q B electron transport. 3-(1-dodecylam inopropyridene)-6- methyl-2H-pyran-2,4-dione (APp12 ), on the other hand, induced an abnormal band peaking at 15 °C between the Q-band and B-band. From the gradual downshift of its peak temperature in titration experiments, this band was assigned to arise from a modified S 2 Q B - charge pair, in which the properties of either Q B - or S 2 is altered. The 15 °C-band showed normal oscillation during the first 2 flashes, but the oscillation was interrupted thereafter. Another therm oluminescence analysis by use of post flash low temperature illumination protocol revealed that APp 12 affects neither Q A to Q B nor Q B 2- to PQ electron transport, but specifically blocks S 3 to S 0 transition. These results indicate that APp12 is a new-type PS II inhibitor.