On the nature of the deactivator of the water-splitting system in photosynthesis

Abstract

In this paper the effect of 1,1-diphenyl-2-picrylhydrazine on the deactivation of the water-splitting system is investigated. The following results have been obtained: 1. 1. In the presence of 10 −5 M 1,1-diphenyl-2-picrylhydrazine (DPPH) the decrease of the relative average oxygen yield per flash ϕ as a function of the dark time between the flashes is strongly accelerated. 2. 2. Under these conditions the amplitude of the absorption change of chlorophyll a I at 705 nm decreases with increasing dark time between the flashes. 3. 3. In the presence of 10 −5 M DPPH, the amplitude of the absorption change of the primary electron acceptor X of the light reaction II, is independent of the frequency of excitation in the range of the decrease of ϕ = f( t d). 4. These results indicate that DPPH accelerates the deactivation of the water-splitting system and that in the presence of this agent the backflow of electrons to S 2 and S 3 occurs between X and chlorophyll a I.