[Membrane-active inhibitors of electron transport in chloroplasts]. / Membranoaktivnye ingibitory élektronnogo transporta v khloroplastakh.

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 defect in cytochrome c553 in non-photosynthetic mutant cells of Chlamydomonas reinhardii]. / O povrezhdenii tsitokhroma c553 v kletkakh nefotosinteziruiushchikh mutantov Chlamydotonan reinhardii.

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.

[Photo-dependent conversions of cytochrome f in bean chloroplasts and leaves treated with polyene antibiotics]. / Fotozavisimye prevrashcheniia tsitokhroma f v khloroplastakh i list'iakh bobov, obrabotannykh polienovymi antibiotikami.

The photo-dependent absorption changes of cytochrome f in bean chloroplasts and native leaves treated with the polyene antibiotics surgumycin and filipin were studied. Upon incubation of the chloroplasts or leaves with the antibiotics the value of the photo-induced signal of cytochrome f decreased considerably; however, the kinetics of the cytochrome oxidation under the effect of the exciting light and dark reduction remained unchanged. An addition of plastocyanin to the suspension of the antibiotic-treated chloroplasts, which contained no artificial donors and acceptors, only slightly increased the absolute value of the photo-induced signal of cytochrome f. An addition of plastocyanin to the chloroplasts containing the dichlorophenolindophenol-ascorbate-methylviologen system, sharply changed the kinetics of the cytochrome f photoconversions. A simultaneous registration of the photo-induced signal of cytochrome f and the photochemical activity of photosystem I of the antibiotic-treated chloroplasts revealed differences in the degree of inhibition of the photosystem I activity and decrease of the absolute value of the cytochrome f signal. The data obtained are discussed in terms of possible alternative pathways of electron transfer in the part of the electron transporting chain under study.

[Ferredoxin-dependent glutamate synthase of Chlorella]. / O ferredoksin-zavisimoi glutamatsintaze khlorelly.

Ferredoxin-dependent glutamate synthase has been found in cells of thermophylic Chlorella strain Ch. pyrenoidosa 82T. The enzyme is active with its own ferredoxin and that of Spirulina. Glutamate synthase activity increases during nitrogen starvation and than decreases in the course of successive ammonium assimilation. The scheme of ammonium assimilation in Chlorella pyrenoidosa 82T cells is proposed.

[Effect of metalloproteins on the photochemical activity of chloroplasts treated with polyene antibiotics]. / Deistvie metalloproteidov na fotokhimicheskuiu aktivnost' khloroplastov, obrabotannykh polienovymi antibiotikami

The effects of various metall-containing proteins (plastocyanin, plantacyanin, azurine and cytochromes of the f type) on the activity of photosystem I of chloroplasts, treated with polyene antibiotics, were studied. The inhibiting effect of the polyenes, surgumycin and philipin, was completely removed by an addition of copper-containing protein plastocyanin. No similar effect was exerted by other Cu-containing proteins--azurine and plantacyanin. The cytochromes of the f type isolated from the green algae chlorella, blue-green algae spiruline and aphanezomenone, having different electrophoretic properties, restored the activity of photosystem I of chloroplasts incubated with antibiotics in a different degree. Acid cytochrome f of chlorella restored the activity by 80--100%; less acid cytochrome f from spiruline-only by 50%. The least restoring effect was exerted by aphanezomenone cytochrome, which possesses some basic properties. The chloroplasts treatment with surgumycin did not affect the isolation of the terminal enzyme of the chloroplast electron-transporting chain of ferredoxin--NADP--reductase. Possible environment of plastocyanin in the chloroplast membrane and the mechanism of photosystem I restoration are discussed.

[Cytochrome f from Chlorella pyrenoidosa Pringsheim 82 T]. / Tsitokhrom f chlorella pyrenoidosa pringsheim l 821

Cytochrome of the f type was isolated from the thermophilous autotrophic strain Chlorella pyrenoidosa Pringsheim 82T and purified on Sephadex G-75. The isolation procedure allowed a simultaneous production of glutamate dehydrogenase isoenzymes. From 100 g of Chlorella wet paste 100 to 120 nM of electrophoretically unicomponent protein with a molecular weight of 12,000 to 13,000 were isolated. The Chlorella cytochrome had an absorption spectrum in the visible light that was typical of the f type cytochromes.