[Membrane-active inhibitors of electron transport in chloroplasts]

The effects of polyene antibiotic amphotericin B and the organophosphorus insecticide chlorophos (trichlorofon) on the electron transport in isolated pea chloroplasts were compared; both compounds were found to inhibit the electron transport. The concentration dependence of the inhibitory effects on the photoreactions in chloroplasts was established. Affer washing of the chloroplasts from amphotericin B admixtures the photoreduction of NADP+ was decreased by 50%, the photooxidation of cytochrome f in situ was affected comparatively little, while the photoreduction of plastocyanin in situ was decreased by 60%. The supernatant after amphotericin B washing contained plastocyanin. An addition of chlorophos to the medium caused a 70% inhibition of NADP+ photoreduction and a 40% inhibition of cytochrome f photooxidation and of plastocyanin photoreduction. It was assumed that the active site of amphotericin B lies in the plastocyanin region, that of chlorophos--at the site of NADP+ photoreduction in photosystem I. Experiments with isolated pea plastocyanin and ferredoxin and cytochrome C553 of Chlorella demonstrated that neither of the inhibitors interacts with the prosthetic groups or with he protein part of these electron carriers. Presumably the mechanism of action of amphotericin B and chlorophos on the photosynthetic electron transport consists in a destruction of chloroplast membrane structures. Using membrane-active inhibitors, the alternative pathways of electron transfer through cytochrome f and plastocyanin were established.