Studies on the mechanism of destabilization of the positive charges trapped in the photosynthetic water-splitting enzyme system Y by a deactivation-accelerating agent.

Abstract

Abstract The mechanism of the 2-(3,4,5-trichloro)anilino-3,5 dinitrothiophene (ANT 2S)-induced cyclic electron flow leading to the discharge of the higher-trapped-hole accumulation states S2 and S3 in the photosynthetic water-splitting enzyme system Y of chloroplasts has been investigated. It was found: 1. 1. Under normal conditions the ANT 2s-catalyzed cycle includes both light reactions. 2. 2. By selective kinetical inhibition of the electron flow through P700—either by histone treatment or by 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone blockage—the ANT 2s-induced deactivation of S2 and S3 is not significantly changed. Hence, System I activity is not a functional prerequisite for the ANT 2s-catalyzed discharge of S2 and S3. 3. 3. The reciprocal half time of the ANT 2s-induced decay of the relative average oxygen yield per flash, as a function of the time td between the flashes representing the degree of the Acceleration of the Deactivation Reactions of the water-splitting enzyme system (ADRY) effect, is nearly linearly related to the ANT 2s concentration within the range of 10−7–10−6 M. 4. 4. In respect to the mode of action of ANT 2s two different types of mechanism have been discussed: fixed-place mechanism and mobile-catalyst mechanism. 5. 5. Based on the experimental data the conclusion has been drawn that the ADRY agent ANT 2s probably acts as a mobile catalyst.