Biomedical subjects

V D Samuilov

Publications and source records attributed to V D Samuilov.

At least 19 recordsLinked to original sources

PubMed2002

Involvement of chloroplasts in the programmed death of plant cells.

The effect of cyanide, an apoptosis inducer, on pea leaf epidermal peels was investigated. Illumination stimulated the CN--induced destruction of guard cells (containing chloroplasts and mitochondria) but not of epidermal cells (containing mitochondria only). The process was prevented by antioxidants (alpha-tocopherol, 2,5-di-tret-butyl-4-hydroxytoluene, and mannitol), by anaerobiosis, by the protein kinase C inhibitor staurosporine, and by cysteine and serine protease inhibitors. Electron acceptors (menadione, p-benzoquinone, diaminodurene, TMPD, DCPIP, and methyl viologen) suppressed CN--induced apoptosis of guard cells, but not epidermal cells. Methyl viologen had no influence on the removal of CN--induced nucleus destruction in guard cells under anaerobic conditions. The light activation of CN--induced apoptosis of guard cells was suppressed by DCMU (an inhibitor of the electron transfer in Photosystem II) and by DNP-INT (an antagonist of plastoquinol at the Qo site of the chloroplast cytochrome b6f complex). It is concluded that apoptosis initiation in guard cells depends on the simultaneous availability of two factors, ROS and reduced quinones of the electron transfer chain. The conditions for manifestation of programmed cell death in guard and epidermal cells of the pea leaf were significantly different.

Apoptosis↗

PubMed2001

Hydrogen peroxide inhibits photosynthetic electron transport in cells of cyanobacteria.

The effect of H2O2 on photosynthetic O2 evolution and photosynthetic electron transfer in cells of cyanobacteria Anabaena variabilis and Anacystis nidulans was studied. The following experiments were performed: 1) directly testing the effect of exogenous H2O2; 2) testing the effect of intracellular H2O2 generated with the use of methyl viologen (MV); 3) testing the effect of inhibiting intracellular H2O2 decomposition by salicylic acid (SA) and 3-amino-1,2,4-triazole (AT). H2O2 inhibited photosynthetic O2 evolution and light-induced reduction of p-benzoquinone (BQ) + ferricyanide (FeCy) in the Hill reaction. The I50 value for H2O2 was ~0.75 mM. Photosynthetic electron transfer in the cells treated with H2O2 was not maintained by H2O2, NH2OH, 1,5-diphenylcarbazide, tetraphenylboron, or butylated hydroxytoluene added as artificial electron donors for Photosystem (PS) II. The H2O --> CO2, H2O --> MV (involving PSII and PSI) and H2O --> BQ + FeCy (chiefly dependent on PSII) electron transfer reactions were inhibited upon incubation of the cells with MV, SA, or AT. The N,N,N,N-tetramethyl-p-phenylenediamine --> MV (chiefly dependent on PSI) electron transfer was inhibited by SA and AT but was resistant to MV. The results show that H2O2 inhibits photosynthetic electron transfer. It is unlikely that H2O2 could be a physiological electron donor in oxygenic photosynthesis.

Amitrole↗

PubMed2000

CN(-)-Induced degradation of nuclei in cells of pea leaves.

Degradation of nuclei in epidermal and guard cells of pea leaves was induced by NaCN. Guard cells were considerably more resistant to CN- than epidermal cells. CN--induced nucleus degradation in guard cells was accelerated by illumination. The effect of illumination was negligible in epidermal cells that, unlike guard cells, do not contain chloroplasts. These data may indicate a role of chloroplasts in CN--induced cell death. CN--induced nucleus degradation in epidermal cells was retarded by antioxidants (butylated hydroxytoluene and vitamin E). The effect of CN- in guard cells was largely removed by vitamin E. Salicylic acid, an inhibitor of catalase and ascorbate peroxidase, induced 100% degradation of nuclei in epidermal cells but did not significantly affect nuclei in guard cells. CN--induced inhibition of catalase and peroxidase is assumed to lead to generation and accumulation of reactive oxygen species inducing apoptosis. Like mitochondria, which play an important role in animal cell apoptosis, chloroplasts may take part in apoptosis in plant cells.

Cell Nucleus↗

PubMed2000

Photoelectric response generated under non-heme iron reduction on the photosystem II acceptor side.

Proteoliposomes containing oxygen-evolving particles of Photosystem II and associated with a planar phospholipid membrane generate a transmembrane electric potential difference (DeltaPsi) induced by a laser flash. With direct electrometrical technique, it was shown that the direction of the electrical field ("minus" inside the proteoliposome) corresponds to acceptor side of the Photosystem II complex facing inside and donor side facing outside of the liposomes. In addition to the fast phase (tau < 0.1 microsec) of the DeltaPsi generation due to electron transfer between YZ of the water-oxidizing complex and the primary plastoquinone QA, a phase with tau approximately 120 microsec and maximum amplitude approximately 30% of the amplitude of the fast phase was observed under the first flash in proteoliposomes containing potassium ferricyanide, which is known as an oxidant of the non-heme iron (Fenh) on the acceptor side of Photosystem II. This additional phase was absent under the second laser flash but was completely restored after 5 min dark adaptation. The phase of the photoelectric response with tau approximately 120 microsec is probably due to electron transfer from QA to Fenh(III) and likely includes a component related to H+ transfer.

Heme↗

PubMed2000

Programmed cell death.

This paper reviews data on programmed cell death (apoptosis) in animals and plants. Necrosis is a pathological scenario of cell death, which entails an inflammatory response in animal tissues. Apoptosis results in the disintegration of animal/plant cells into membrane vesicles enclosing the intracellular content, which are thereupon engulfed by adjacent or specialized cells (phagocytes) in animals. Plants lack such specialized cells, and plant cell walls prevent phagocytosis. The paper considers the main molecular mechanisms of apoptosis in animals and the pathways of activation of caspases, evolutionarily conserved cysteine proteases. A self-contained section concerns itself with the process of programmed cell death (PCD) in microorganisms including: 1) cell death in the myxomycete Dictyostelium discoideum and the parasitic flagellate Trypanosoma cruzi; 2) PCD in genetically manipulated yeast expressing the proapoptotic Bax and Bak proteins; 3) the death of a part of a prokaryotic cell population upon the depletion of nutrient resources or under stress; 4) the elimination of cells after a loss of a plasmid encoding a stable cytotoxic agent in combination with an unstable antidote; and 5) PCD in phage-infected bacterial cells.

Animals↗

PubMed2000

Isolation and properties of peroxidase produced by the fungus Panus tigrinus.

Synthesis of peroxidase and laccase by the fungus Panus tigrinus was significantly stimulated by addition of the lignocellulose substrate to the culture media. Peroxidase was isolated from the culture liquid and some properties of the enzyme were investigated. P. tigrinus peroxidase belongs to a group of extracellular peroxidases similar to the plant type peroxidases.

Cellulose↗

PubMed1999

Lag phase of CO2-dependent O2 evolution by illuminated Anabaena variabilis cells.

The steady-state rate of CO2-dependent O2 evolution by Anabaena variabilis cells in response to illumination was established after a lag phase. The lag phase was shortened (1) in cells incubated with glucose as an oxidizable substrate and (2) upon an increase in light intensity. The lag phase was absent during electron transfer from H2O to p-benzoquinone (in combination with ferricyanide) involving Photosystem II. A lag was observed during electron transfer from H2O to methyl viologen involving Photosystems II and I, but not for electron transfer from N,N,N',N'-tetramethyl-p-phenylenediamine (in combination with ascorbate) to methyl viologen involving only Photosystem I. The lag phases of the light-induced H2O --> CO2 and H2O --> methyl viologen electron transfer reactions showed the same temperature dependences at 10-30 degrees C. The lag was prevented by 3-(3,4-dichlorophenyl)-1,1-dimethylurea at concentrations that caused partial inhibition of photosynthetic O2 evolution. Retardation of cell respiration by a combination of CN- and benzylhydroxamate shortened the lag phase of the H2O --> methyl viologen electron transfer. It is concluded that the lag phase is associated with the electron transfer step between Photosystem II and Photosystem I common for the photosynthetic and respiratory chains and is due to the stimulation of cell respiration during the initial period of illumination as a consequence of an increase in the reduced plastoquinone pool and to subsequent retardation of respiration resulting from the transition of the electron transfer chain to the competitive pathway involving Photosystem I.

Anabaena↗

PubMed1999

Hydrogen peroxide inhibits the growth of cyanobacteria.

H2O2 at concentrations of 10(-5)-10(-4) M suppresses phototrophic growth of Anacystis nidulans and Anabaena variabilis in dialysis culture. The growth of the cyanobacteria resumed after a long adaptation period. In batch cultures, the growth of A. nidulans and A. variabilis was suppressed after one-time addition of 10(-2)and 10(-3)-10(-2) M H2O2, respectively. Inducing intracellular H2O2 formation by adding methylviologen, vitamin K3, or phenazine methosulfate suppresses the growth of both cyanobacteria. The catalase inhibitor salicylic acid suppresses the growth of A. nidulans and A. variabilis at a concentration of 5.10(-3) M. The data suggest an inhibitory effect of H2O2 on the growth of the cyanobacteria. H2O2 is unlikely to serve as an electron donor during photosynthesis.

Anabaena↗

PubMed1998

Quenching of chlorophyll fluorescence by quinones.

Quinones caused quenching of Chl a fluorescence in native and model systems. Menadione quenched twofold the fluorescence of Chl a and BChl a in pea chloroplasts, chromatophores of purple bacteria, and liposomes at concentrations of 50-80 microM. To obtain twofold quenching in Triton X-100 micelles and in ethanol, the addition of 1.3 mM and 11 mM menadione was required, respectively. A proportional decrease in the lifetime and yield of Chl a fluorescence in chloroplasts, observed as the menadione concentration increased, is indicative of the efficient excitation energy transfer from bulk Chl to menadione. The decrease in the lifetime and yield of fluorescence was close to proportional in liposomes, but not in detergent micelles. The insensitivity of the menadione quenching effect to DCMU in chloroplasts, and similarity of its action in chloroplasts and liposomes indicate that menadione in chloroplasts interacts with antenna Chl, i.e., nonphotochemical quenching of fluorescence occurs.

Bacterial Chromatophores↗

PubMed1995

Photoreduction of silicomolybdate in chloroplasts by agents accelerating the deactivation reactions of the water-oxidizing system.

Uncouplers of photosynthetic phosphorylation, CCCP, TTFB and PCP, inhibited light-induced O2 evolution in the Hill reaction with SiMo (I50 approximately 20, 3 and 45 microM, respectively), but only insignificantly diminished SiMo photoreduction by pea chloroplasts. The same properties were exhibited by the ADRY agent ANT2p. CCCP, TTFB and PCP are oxidizable compounds with redox potentials of +1.17, +1.18 and +1.09 V (pH 6.0), as determined by cyclic voltammetry. Similarly to NH2OH, the tested uncouplers can apparently serve as electron donors for photosystem II.

Chloroplasts↗

PubMed1994

Electrogenicity at the secondary quinone acceptor site of cyanobacterial photosystem II.

Flash-induced generation of the electric potential difference (delta psi) by a direct electrometrical method was studied in Anacystis nidulans photosystem II-containing proteoliposomes associated with a phospholipid-impregnated collodion film. Besides a rapid phase of delta psi generation corresponding to charge separation between P680 and QA, an additional electrogenic phase with a characteristic time of 0.27 ms at pH 7.0 was observed after the second laser flash. The maximal amplitude of this phase was approx. 4% of that related to the P680+QA- formation. The sensitivity of this phase to DCMU, the flash-number dependence of its amplitude as well as the amplitude and the rate constant pH-dependences, indicate that it is due to the dismutation of QA- and QB- and to subsequent protonation of a doubly reduced plastoquinone QB2-.

Cyanobacteria↗

PubMed1993

Interaction of carbonyl cyanide m-chlorophenylhydrazone with the photosystem II acceptor side.

We show that CCCP, known as an uncoupler of photophosphorylation and an ADRY agent, inhibits FeCy photoreduction and coupled O2 evolution by isolated chloroplasts equally (I50 approximately 2 microM), but is practically without effect on the O2 evolution coupled with SiMo reduction within the 0.2-10 microM concentration range. CCCP has no effect on the nanosecond chlorophyll fluorescence in chloroplasts incubated at low light intensity, but decreases it at high light intensity. The electron transfer from reduced TMPD or duroquinol to methylviologen is resistant to CCCP. The efficiency of the CCCP inhibitory action on the FeCy photoreduction depends on the rate of electron flow, which is controlled by the light intensity. The data obtained show that CCCP is oxidized by the photosystem II donor side and is reduced by QP, competing for electrons with FeCy and the cytochrome blf complex.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗

PubMed1992

Technical bioenergetics and ecosystem biotechnology.

The present work explores some possible practical uses of bioenergetic processes (fermentation, respiration and photosynthesis) in the microbial cell for the purpose of renewable fuel production. These considerations are based on ecosystem biotechnology which include the following main points: 1. Creation of closed energy-transducing ecosystems under laboratory conditions. 2. Production of renewable energy carriers with the help of microbial communities (e.g., mixed cultures of microorganism). 3. Investigation of the role of the individual microoganism in the population or community.

Bacteria↗

PubMed1991

[Dependence of Bacillus subtilis cell respiration on monovalent cations].

Nigericin, monensin, valinomycin + carbonyl-cyanide-m-chlorophenylhydrazone and gramicidin inhibit the respiration of Bacillus subtilis cells incubated with NAD-dependent substrates or succinate, but not with ascorbate + N,N,N',N'-tetramethyl-p- phenylene-diamine. The level of inhibition was decreased by potassium ions and, in a lower degree, by sodium or ammonium ions. The results obtained suggest that the respiration of Bacillus subtilis depends on the presence of monovalent cations whose effects seem to be directed at complexes I, III and probably complex II of the respiratory chain.

Bacillus subtilis↗

PubMed1990

Effect of polyelectrolytes on serine proteinase secretion by Bacillus subtilis.

Addition of polycations with molecular masses of 5-40 kDa as well as Na+, stimulated serine proteinase secretion by Bacillus subtilis cells. Polyanions and higher-molecular-mass polycations (100-200 kDa) were inefficient. The enzyme yields in the presence of polycations or Na+ were equal in magnitude. The results indicate that the cations, apparently counteracting the negative surface charge of the bacterial plasma membrane, cause the desorption of the serine (alkaline) proteinase. The synthesis of the proteinase is inferred to be stopped as the enzyme is bound to the outer surface of the plasma membrane. The desorption of the enzyme thus induces the synthesis of the new portions of proteinase.

Bacillus subtilis↗

PubMed1990

[The surface membrane charge of bacteria and its role in serine proteinase secretion by Bacillus subtilis cells].

Univalent, bivalent and trivalent metal cations increase the fluorescence yield of 9-aminoacridine in the suspensions of chromatophores of the purple nonsulfur bacterium Rhodospirillum rubrum isolated thylakoid membranes and cells of cyanobacterium Anabaena variabilis, cells Bacillus subtilis. The active cation concentrations increase about in 10 times with the decrease of their valency by one. It points to the fact that the changes in 9-aminoacridine fluorescence serve for the monitoring of the surface charge of bacterial membranes. The negative surface charge of B. subtilis cells increases before the onset of the serine protease secretion. The metal cations stimulate the serine protease secretion by B. subtilis cells, the stimulating effect correlates with the action of cations on the 9-aminoacridine fluorescence yield. It is suggested that the surface charge of cytoplasmic membrane regulates the formation and release of serine protease by the cells of B. subtilis.

Aminacrine↗

PubMed1988

[Quinones and their interactions with enzyme complexes of energy-transducing biomembranes].

The functionally essential properties of biomembrane quinones and the mechanism of their interaction with protein components are discussed. The hypotheses on the mobile quinone pool or the ability of protein-bound quinones to transfer redox equivalents in biomembranes are discussed. The idea of quinone domains is invoked, and evidence is provided for the presence of such domains in operative biomembranes.

Animals↗

PubMed1983

The dibromothymoquinone effect on membrane potential generation in Rhodospirillum rubrum chromatophores.

2,5-Dibromo-3-methyl-6-isopropyl benzoquinone (DBMIB) inhibits the light-dependent membrane potential generation in Rhodospirillum rubrum chromatophores. The inhibition is relieved by electron donors and is obviously due to oxidation of the photosynthetic electron transfer chain components. In addition, high DBMIB concentrations elicit another effect probably caused by disruption of quinone functions in chromatophores. However, in quinone-depleted chromatophores and proteoliposomes containing the P-870 reaction center and light-harvesting antenna complexes, DBMIB stimulates membrane potential generation in the light, probably restoring some of the quinone-dependent processes in the membrane. DBMIB inhibits the inorganic pyrophosphate- and ATP-induced membrane potential generation in chromatophores.

Adenosine Triphosphate↗