Inhibition of electron transport in chloroplasts between the two photosystems by a water-soluble carbodiimide

Abstract

1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide, which is water soluble, had little effect on electron flow and phosphorylation when chloroplasts were incubated in the dark with this reagent. In contrast, an irreversible inhibition of these reactions was observed in chloroplasts illuminated in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. The inhibition of phosphorylation appeared to be the result of inhibition of electron flow rather than of a phosphorylation reaction itself since the treatment of chloroplasts with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide in the light did not inhibit phosphorylation induced by an acid-to-base transition in the dark. Electron flow from water to ferricyanide, water to methyl viologen, and diaminodurene to methyl viologen (in the presence of 3,4-dicholorophenyl-1,1-dimethyl urea) was sensitive to 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. In contrast, the reduction of diaminodurene and the oxidation of endogenous cytochrome f were not inhibited by the prior exposure of chloroplasts to 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide in the light. It is concluded that 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide attacks a component in the chloroplast electron-transport chain in the region between plastoquinone and cytochrome f.