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Biomedical subjects

M G Gol'dfel'd

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

At least 19 recordsLinked to original sources
PubMed1983

[Effect of endogenous phosphate on electron transfer in chloroplasts].

The chloroplasts with an extremely low content of endogeneous inorganic phosphate have been isolated by appropriate physiological pretreatment of pea or bean plants (intense illumination at a moderately low temperature during blossoming). The electron transport activity of these preparations as measured by ferricyanide or methylred photoreduction is almost completely blocked until exogeneous phosphate is added to the incubation mixture. Low concentrations of phosphate are also necessary for maintaining the stability of chloroplasts and for inhibition of the light-induced degradation of the photosynthetic apparatus.

Chloroplasts↗
PubMed1980

[Photophosphorylation involving chlorophyll adsorbate, separation of light and dark stages].

Upon illumination of the system containing chlorophyll a+b adsorbed on a SiO2 sorbent, ADP and Pi in an aqueous solution, pH 7.6, the formation of ATP has been demonstrated, using 32P-phosphate. This process is inhibited in the absence of oxygen or in the presence of ascorbate. Under similar conditions without ADP pyrophosphate is formed; substitution of ADP for arginine results in a formation of arginine phosphate. Phosphorylation with a reduced yield has also been found upon illumination of chlorophyll adsorbate without other additives and an addition of ADP+Pi solution in the dark to the preilluminated adsorbate fast enough to prevent the decay of the light-induced product. A model according to which the chlorophyll-sensitized oxidation of orthophosphate ion the primary event in the reaction sequence, and the decomposition of orthophosphate radical anion into methaphosphate and hydroxyl species is the secondary step, has been proposed. A possible significance of the results obtained is discussed in terms of the concepts on the prebiotic evolution of energy metabolism.

Adenosine Diphosphate↗
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↗