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Biomedical subjects

M G Gol'dfel'd

Publications and source records attributed to M G Gol'dfel'd.

17 recordsLinked to original sources
PubMedDate not supplied

[Reduction paths of reaction centers of photosystem I of photosynthesis].

The behaviour of ESR signal I in blue-green algae and chloroplasts is considered under various illumination and with various previous treatment. It is shown that the main process determining the kinetics of P700 plus reduction is the reaction with reduced components of the electron transfer chain between the two photosystems. If the accumulation of the products is inhibited by any way, then the reduction rate depends on the reactions with reducing agents in the incubation medium accumulated under irradiation before experiment. These exogenic reducing agents may be removed from the chloroplasts with repeated washings, and from algae-by means of the dark incubation for a long time. The relation of cyclic and noncyclic electron transfer is considered with and without artificial cyclic flow mediator.

Chloroplasts↗
PubMedDate not supplied

[Kinetics of dark reduction of P700 centers in photosynthesis].

Relationship between the rate of dark fall of ESR I signal in the chloroplasts and light intensity 710 nm was studied. It is shown that the kinetics of the signal drop at sufficiently high levels of intensity is a biphase one. The fast phase (2 sec) disappears in the presence of an inhibitor of noncyclic electron transfer. It is concluded that the kinetics of electron transport is not described within the concept of the linear chain of electron carriers and a suggestion is put forward concerning a possible mechanism of this process which depends on the participation of plastoquinone in electron transport.

Chloroplasts↗
PubMedDate not supplied

[2 types of reduction of P700+ reaction centers in the leaves of green plants].

It is shown that in the leaves of Hibiscous sp. the ESR signal I rises under weak far red light after its partial inhibition with a short white flash is slower than after adaptation to 710 nm light and short dark exposition. It is suggested that this divergence in the ESR kinetics is due to the fact that only part of reduced intermediates generated by the photosystem 2 under flash is readily available to P700+, whereas other reducing reagents slowly react with the photosystem 1 reaction centres.

Binding Sites↗
PubMedDate not supplied

[Paramagnetic centers and photochemical reactions of photosystem 2 subchloroplast fragments].

ESR signals of highly purified subchloroplast fragments containing the Photosystem 2 (PS 2) were obtained. Reversibility of the ESR II signal in darkness in the presence of dichlorophenolindophenol (DCPIP) was observed. Reduction of DCPIP with chloroplast fragments in the absence of exogenous donors takes place in light without simultaneous liberation of O2. Electron transfer may be blocked by the displacement of manganese with Mg2+ and Ba2+ bivalent cations. Cd2+ cations partially suppress the electron transfer catalysed by PS 2. The inhibiting effect of Cd2+ is removed in the presence of exogenous Mn2+ or hydroxylamine.

2,6-Dichloroindophenol↗
PubMedDate not supplied

[Light-dependent reactions of Mn2+ and P700+ in chloroplasts during flash illumination].

The changes of the light-induced ESR signal I and exogeneous Mn2+ ions in chloroplasts of Vicia faba plants have been studied under short flash excitation and weak background far red illumination. It is shown that Mn2+ ions reactivate the noncyclic electron transport in chloroplast previously inactivated with high tris concentrations under pulse illumination. Simultaneously with P700+ reduction the ESR signal of free Mn2+ ions decays stoichometrically to P700+ reduction.

Binding Sites↗
PubMedDate not supplied

[Effect of ferricyanide, dark adaptation and aging on the properties of the EPR I signal of chloroplasts].

Ferricyanide (10-3 M) is shown to oxidize from 25 to 50% of the total P700 pool in the dark. The ferri-ferrocyanide mixture thus obtained, acting as redox buffer, accelerates the P700+ dark reduction after continuous far red illumination is turned off or after a saturating flash. The oxidized P700 yield on the flash increase in the presence of ferricyanide as a result oxidation of species in the neighborhood of P700 centers. During aging (24 h at 2--3 degrees in the dark) the yield of flash-induced P700 oxidation also increases thus indicating the loss of cyclic electron flow in aged chloroplasts.

Chemical Phenomena↗
PubMedDate not supplied

[Molar extinction of pigment in the reaction center of photosystem II chloroplasts].

The absolute spin number in the Photosystem I chloroplast fragments from Vicia faba plant photooxidized in the presence of silicomolybdate has been carefully measured by means of camparison of ESR signals of P680-centers and of nitroxyl free radical aqueous solution. The data obtained together with simultaneous measurement of light-induced bleaching centered at 680 nm have been used to determine the molar extinction of reduced P680-center epsilon680 = 0.66 . 10(5) M-1 cm-1.

Binding Sites↗
PubMedDate not supplied

[Light-dependent paramagnetic center in photosystem 2 of higher plants].

In subchloroplast fragments of photosystem II from Vicia faba, free from P700 contamination, a free-radical ESR signal (singlet of 9 G peak-to-peak line-width, g approximately 2,0025) appears under illumination in presence of silicomolybdate as electron acceptor. Using ESR-active electron donors and acceptors as well as conventional redox reagents Hill activity of preparations has been evaluated under different conditions. Evidences are presented that the light-induced dark-reversible silicomolybdate-dependent ESR signal is of the same origin as photobleaching centered at 680 nm which has been earlier interpreted as a result of P680 center of photosystem II oxydation. The relaxation properties of this paramagnetic center as measured by microwave power saturation are different from that of P700+-center in photosystem I.

Binding Sites↗
PubMedDate not supplied

[Phosphorylation in acid shocked chloroplasts].

ADP phosphorylation up to 2.5 nmol per mg of chlorphyll has been found in chloroplasts from Vicia faba plants when the suspension was sharply acidified from pH 8 to pH 1.6 with excess of HC1/KC1 solution. This fact appears to be due to confromation relaxation of the coupling factor under acid-induced denaturation. Heat pretreatment inhibits this effect.

Adenosine Diphosphate↗
PubMedDate not supplied

[Magnetic relaxation of water protons and the state of the water photodissociation system in chloroplasts].

The spin-spin relaxation time T2 of water protons is measured in chloroplast suspensions. It is shown that chloroplast lamellae efficiently increase the rate of proton magnetic relaxation, this effect being a linear function of chloroplast concentration. There is a fast exchange between the water molecules in different environments, thus the measured relaxation rate is a weight average of all water molecules. The rate of proton relaxation is decreased when membrane bound manganese is removed from chloroplasts by tris-washing procedure. The relaxation effect is slightly reduced in the presence of Photosystem II electron acceptors.

2,6-Dichloroindophenol↗
PubMedDate not supplied

[Efficiency of photophosphorylation in chloroplasts with steady and pulsed illumination].

The quantum yield of noncyclic photophosphorylation in chloroplasts excited by a series of 8 mus flashes of the saturating intensity displays a two-fold decrease when the flash-frequency is reduced from about 1.1 to about 0.8 s-1, whereas further decrease of flash frequency does not affect the average ATP yield per flash. Under excitation by two-flashes series the ATP yield is also about half-maximal. These observations are inconsistent with the concept postulating accumulation of energy contributions from several parallel or consecutive one-electron transfers as a prerequisite for ATP formation. The two-state model of a thylakoid membrane and of a coupling site is put forward according to which only one of these states ensures ATP formation in response to one electron transfer through one coupling site, whereas the other state is nonphosphorylating.

Adenosine Triphosphate↗