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

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-l,3-dione (A C m l2 ) converted the B-band (30 °C) arising from S2Q | 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 S2QA recom bination, indicating that these two compounds block 0 A to Q b electron transport. 3-(l-dodecylam inopropyridene)-6methyl-2H-pyran-2,4-dione (A P p l2 ), 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 S2Q B charge pair, in which the properties o f either Q i or S2 is altered. The 15 °C-band showed normal oscillation during the first 2 flashes, but the oscillation was interrupted thereafter. Another thermoluminescence analy­ sis by use of post flash low temperature illumination protocol revealed that A P p l2 affects neither Q a to Q b nor Q^to PQ electron transport, but specifically blocks S3 to Sn transition. These results indicate that A P p l2 is a new-type PS II inhibitor.