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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.

The effect of dibromothymoquinone on photosynthetic electron transport in pea dependent on concentration was studied. Dibromothymoquinone inhibited general electron transport from water to NADP+ in isolated chloroplasts and ethiochloroplasts and the electron transfer via plastoquinone and cytochrome f in the leaves and isolated plastids. At all concentrations studied dibromothymoquinone significantly affected the absorption changes at 590 nm in the ethiochloroplasts associated with plastocyanine photoreactions. Possible location of electron carriers in the photosynthetic electron transport chain is discussed.

Light-induced redox conversions of cytochrome f and plastocyanin in situ and electron transporst from H2O to NADP+ were studied by a dual-wave differential spectrophotometry under identical conditions and subsequently compared. The analysis in red and far red light, treatment by inhibitors, e. g. diurone and dibromothymoquinone, and the analysis of photoreactions during the greening of etiolated seedlings demonstrated that cytochrome f functions only in the non-cyclic chain of electron transport, whereas plastocyanin--both in the non-cyclic and in the cyclic electron transport chains. The jositions of cytochrome f and plastocyanin in various electron-transport chains are proposed.

Phloridzin (2',4',6',4-tetraoxyhydrochalcon-2'-glucoside) was used to study the localization of synthesis of ATP in the electrontransporting chain of photosynthesis. It was shown that phloridzin inhibits the rate of photoreduction of NADP+ by isolated pea chloroplasts by 40%, electron transport via cytochrome f by 100% and via plastocyanin--by 50%. The "crossover" experiments demonstrated that phloridzin inhibits ADP-induced photoreduction of cytochrome f, having no effect on plastocyanin under identical conditions. It is assumed that the site of ATP synthesis is localized on the reduced site of cytochrome f, while the carrier itself is located in the electron transporting chain coupled to phosphorylation. It is possible that only part of the plastocyanin molecules are located in the phosphorylating pathway of electron transport.

The light electron transport in non-photosynthetic mutants of Chlamydomonas reinhardii A-36 and A-68 with a decreased content of cytochrome c553 was studied. The light-induced changes of absorption at 520, 559, 563 nm were shown to occur in the films of intact cells and in cell fragments. However, no maximum of the "light minus dark" difference absorption spectra of mutants belonging to cytochrome c553 was revealed. The electron transport from water to NADP+ or ferricyanide in the mutants was completely blocked; however, it was partly restored by an addition of exogenous cytochrome c553 to the cell fragments. A conclusion on the genetic damage of cytochrome c553 in mutants A-36 and A-68 was made. The localization of the cytochrome in the electron transport chain between the photosystems was demonstrated.

The interrelationship between biochemical photosynthetic reactions and mutations was investigated, using five nuclear recessive lethal pea mutants with damaged photosystems II (1, 19) and I (5, 21, 22). Based on the data from photoreduction of NADP+, light-induced redox conversions of exogenous and endogenous plastocyanines in isolated chloroplasts, light-induced redox conversions of cytochrome f and absorbance changes at 520 nm in chloroplasts and leaves, the possible existence of alternative pathways of electron transfer and the pleiotropic effects of mutations, are discussed. A correlation between the structural damages of chloroplasts and the photochemical activity of mutants was found. The existence of cyclic electron transport around photosystem I involving cytochrome f and plastocyanine in mutants 1 and 19 and of an electron transfer pathway from H2O to NADP+ without plastocyanine in mutant 22 is postulated.