[Two molecular forms of pea ferredoxin in the electron transport chain of chloroplasts]. / Osobennosti funktsionirovaniia dvukh molekuliarnykh form ferredoksina gorokha v tsepi élektronnogo transporta khloroplastov.

The effects of two molecular forms of water-soluble ferredoxin (Fd I and Fd II) on the kinetics of electron transport in bean chloroplasts (class B) were studied. The light-induced redox transitions of the photosystem I reaction center P700 were measured by the intensity of the EPR signal I produced by P700+. Both forms of ferredoxin, Fd I and Fd II, when added to the chloroplasts in catalytic amounts, stimulate the light-induced electron transfer from P700 to NADP+. Nevertheless, Fd I is a better mediator of the back reactions from NADPH to P700+. This electron transfer pathway is sensitive to the cyclic electron transport inhibitor, antimycin A, and to DCMU inhibitor of electron transport between photosystem II and plastoquinone. It may be concluded that the two molecular forms of ferredoxin, Fd I and Fd II, differ in their ability to catalyze cyclic electron transport in photosystem I. The role of Fd I and Fd II in regulation of electron transport at the acceptor site of photosystem I is discussed.

[Correlation between non-cyclic and pseudocyclic electron transport in pea chloroplasts: dependent on the concentration of ferredoxin]. / Sootnoshenie mezhdu netsiklicheskim i psevodotsiklicheskim transportom élektronov v khloroplastakh gorokha v zavisimosti ot kontsentratsii ferredoksina.

The effects of ferredoxin concentrations on the correlation between pseudocyclic and non-cyclic electron transport in isolated pea chloroplasts with NADP+ as an electron acceptor was studied. The correlation of psuedocyclic and non-cyclic electron transport upon photoreduction of NADP+ in vitro can be regulated by ferredoxin concentration. At ferredoxin concentrations studied an addition of NADP+ to the system which makes possible electron transfer from ferredoxin to ferredoxin-NADP+-reductase increases the rate of overall electron transport across the chain. Unlike the pseudocyclic electron transport, photoreduction of NADP+ reaches its maximal saturation at relatively low (10-15 microM) concentrations of ferredoxin (Km = approximately 2-5 microM).

[Participation of its reaction center in the electrochemical reduction of ferredoxin]. / Ob uchastii v élektrokhimicheskom vosstanovlenii ferredoksina ego reaktsionnogo tsentra.

In the experiments with reaction center modification of ferredoxin its participation in reduction has been shown. Polarographic characteristics of ferredoxin and apoferredoxin have been compared. While removing iron and labile sulphur from ferredoxin reaction center the reduction wave of Fe-S bonds with E 1/2 = -0.33 V (N. H. E.) transforms into the reduction wave of S-S bonds with E 1/2 = -0,39 V at pH = 7.

[Role of ferredoxin in pseudo-cyclic electron transport in isolated pea chloroplasts]. / Uchastie ferredoksina v psevdotsiklicheskom elektronnom transporte v izolirovannykh khloroplastakh gorokha.

The pseudo-cyclic electron transport in isolated pea chloroplasts in a medium without exogenous cofactors but containing methylviologen and ferredoxin was studied. In order to establish the steps limiting the electron transport, the rates of electron transport a different pH values and under phosphorylating and non-phosphorylating conditions in the presence of the uncoupler--gramicidin D--were determined. It was shown that in the absence of exogenous cofactors the total electron transport is limited by a stage of electron transfer from the acceptor site of photosystem I to oxygen. An addition of ferredoxin or methylviologen stimulates oxygen consumption. It was shown that the plot of the dependence of the rate of oxygen consumption on ferredoxin concentration is two-phase in contrast to that of methylviologen concentration, which is indicative of the existence of two competitive reactions of oxygen reduction involving ferredoxin (with different Km values for the protein).

[Effects of specific reagents and urea on the reactivity of non-heme iron and thiol groups of pea and corn ferredoxins]. / Reaktsionnaia sposobnost' negemovogo zheleza i tiolovykh grupp ferredoksinov gorokha i kukuruzy pri deistvii spetsificheskikh reagentov i mocheviny.

The reactivities of the SH-groups of pea and corn ferredoxins were found to be different. One or two SH-groups in the molecule of pea ferredoxin and one SH-group in the molecule of corn ferredoxin are readily available for the thyol group specific reagents. Four SH-groups of both ferredoxins are completely masked, i. e. available for the thyol reagents only after protein denaturation in the presence of urea. The rates of SH-group interaction with the sulfhydryl reagents in corn ferredoxin are lower than those in pea ferredoxin. The non-haem iron of pea ferredoxin interacts with the complex formers far more rapidly as compared to corn ferredoxin. The ferredoxins tested differ in the amount of iron atoms. The latter require the presence of oxygen for their complete interaction with the complex formers.

Characterization of plastocyanin from corn (Zea mays L.) and pea (Pisum sativum L.) leaves.

A comparison of plastocyanin isolated from pea and corn leaves was made according to a number of indices. No appreciable differences were detected between the proteins in molecular weight or sedimentation constants. In addition, it was shown that plastocyanin of corn, in comparison with the pea protein, possesses greater thermal stability, is more resistant to the action of high and low H+ ion concentrations, as well as to the action of concentrated solutions of urea and guanidine nitrate. The detected differences indicate peculiarities in the molecular organization of plastocyanins from various groups of plants. It is suggested that the differences noted in the structure of plastocyanins can ensure effective functioning of proteins under nonuniform conditions of the external environment.

[Ferredoxin reduction by polarographic methods]. / O vosstanovlenii ferredoksina poliarograficheskimi metodami

The reduction of iron-sulphur protein of the higher plant ferrodoxin has been studied by polarographical methods. Ferredoxin initiates a reversible wave with E1/2=--0,61 v (N. C. E.) at pH 7. Protein absorption greatly influences the electrochemical reduction. The protons have been shown to take part in the electrode reaction. The potentiometrically obtained data about the difference between E1/2 and E0=--0.70 v and its causative factors are discussed. As a result of the experiments with modification of ferredoxin active centre it has been concluded that the active centre participates in the polarographical reduction.