PHOTOREDUCTION OF SILICOMOLYBDATE IN CHLOROPLASTS BY AGENTS ACCELERATING THE DEACTIVATION REACTIONS OF THE WATER-OXIDIZING SYSTEM

Uncouplers of photosynthetic phosphorylation, CCCP, TTFB and PCP, inhi bited light-induced O-2 evolution in the Hill reaction with SiMo (I-50 similar to 20, 3 and 45 mu M, respectively), but only insignificantly diminished SiMo photoreduction by pea chloroplasts. The same properti es mere exhibited by the ADRY agent ANT2p. CCCP, TTFB and PCP are oxid izable compounds with redox potentials of +1.17, +1.18 and +1.09 V (pH 6.0), as determined by cyclic voltammetry. Similarly to NH2OH, the te sted uncouplers can apparently serve as electron donors for photosyste m II.