Biomedical subjects

A B Rubin

Publications and source records attributed to A B Rubin.

At least 19 recordsLinked to original sources

PubMed2001

Light-triggered pH banding profile in Chara cells revealed with a scanning pH microprobe and its relation to self-organization phenomena.

When exposed to light, Characean cells develop a pattern of alternating alkaline and acid bands along the cell length. The bands were identified with a tip-sensitive antimony pH microelectrode positioned near one end of Chara internode at a distance of 50-100 microm from the cell wall. The stage with Chara cell was moved along its longitudinal axis at a computer-controlled speed (100 or 200 microm s(-1)) relative to the pH probe over a distance of 50 mm. Under sufficient uniform illumination of the cell (from 100 to 2.5 Wm(-2)), the homogeneous pH distribution becomes unstable and a banding pattern is formed, the spatial scale of which decreases with the light intensity. If the cell is locally illuminated, bands are formed only in the region of illumination. It is shown that the inhibition of cyclosis by cytochalasin B leads to the disappearance of the banding pattern. The addition of ammonium (weak base) inhibited the banding pattern, whereas acetate (weak acid) alleviated the inhibitory effect of ammonium and restored the pH banding. A model explaining the observed phenomena is formulated in terms of proton concentration outside and bicarbonate concentration inside the cell. It contains two diffusion equations for the corresponding ions with nonlinear boundary conditions determined by ion transport processes across the cell membrane. The model qualitatively explains most of the experimental observations. It describes the dependence of the pattern characteristics on the light intensity and reveals the role of cyclosis in this phenomenon.

Antimony↗

PubMed2001

Comparative study on photosynthetic activity of chloroplasts in acid and alkaline zones of Chara corallina.

A novel experimental approach has been applied to investigate the relationship between pH banding in Chara cells and photosynthetic activity of chloroplasts located in cell regions adjacent to acid and alkaline bands. The combination of pH microelectrode technique with pulse amplitude modulation (PAM) microfluorimetry enabled parallel measurements of longitudinal pH profiles and chlorophyll fluorescence yield in acid and alkaline zones of individual Chara cells. The scanning with a pH-microelectrode along the cell length revealed the light-dependent pH pattern, i.e., alternating acid and alkaline bands with pH differences as large as 2 - 3 pH units. In parallel, measurements of chlorophyll fluorescence yield under actinic light were performed using PAM microfluorometry. It was found that the effective photochemical yield of photosystem II is substantially higher in acid than in alkaline zones. The results clearly show that the banding pattern is not confined solely to the plasmalemma but is also exhibited in alternating photosynthetic performance of the underlying chloroplast layer. Apparently, the acid regions enriched with CO2 ensure sufficient flow of this substrate to the Calvin cycle reactions, thus promoting the photosynthetic rate, whereas the alkaline zones devoid of CO2 favor radiative losses of absorbed solar energy in chloroplasts.

Chloroplasts↗

PubMed2001

Effect of D2O and cryosolvents on the redox properties of bacteriochlorophyll dimer and electron transfer processes in Rhodobacter sphaeroides reaction centers.

Effects of environmental changes on the reaction pattern of excitation energy trapping and transformation into the "stable" radical pair P+Q(A)-, have been analyzed in isolated reaction centers of the anoxygenic purple bacterium Rhodobacter sphaeroides. The following results were obtained: (a) replacement of exchangeable protons by deuterons significantly retarded the electron transfer steps of primary charge separation, leading to the radical pair P+I- and of the subsequent reoxidation of I- by the quinone acceptor Q(A) but has virtually no effect on the midpoint potential of P/P+ that was found to be 430+/-20 mV; (b) addition of 70% (v/v) glycerol causes a shift of Em by about 30 mV towards higher values whereas the kinetics of the electron transfer reactions remain almost unaffected; (c) in the presence of the cryoprotectant DMSO, a combined effect arises, i.e. a retardation of the electron transfer kinetics comparable to that induced by H/D exchange and simultaneously an upshift of the Em value to 475+/-20 mV, resembling the action of glycerol. These results are discussed within the framework of effects on the midpoint potential due to the dielectric constant of the medium and changes of the charge distribution in the vicinity of the redox groups and the influence of relaxation processes on electron transfer reactions.

Bacteriochlorophylls↗

PubMed2001

Effects of extraction of the H-subunit from Rhodobacter sphaeroides reaction centers on relaxation processes associated with charge separation.

Effects of extraction of the H-subunit from Rhodobacter sphaeroides photosynthetic reaction centers (RC) on the characteristics of the photoinduced conformational transition associated with electron transfer between photoactive bacteriochlorophyll and primary quinone acceptor were studied. Extraction of the H-subunit (i.e., the subunit that is not directly bound to electron transfer cofactors) was found to have a significant effect on the dynamic properties of the protein--pigment complex of the RC, the effect being mediated by modification of parameters of the relaxation processes associated with charge separation.

Darkness↗

PubMed2001

Comparative study of thermal degradation of iron-sulfur proteins in spinach chloroplasts and membranes of thermophilic cyanobacteria: mössbauer spectroscopy.

Mössbauer spectra of chloroplasts isolated from spinach plants grown in a mineral medium enriched with 57Fe and Mössbauer spectra of native membranes of the thermophilic cyanobacterium Synechococcus elongatus contain a broad asymmetric doublet typical of the iron-sulfur proteins of Photosystem (PS) I. Exposure of chloroplasts to temperatures of 20-70 degrees C significantly modifies the central part of the spectra. This spectral change is evidence of decreased magnitude of the quadrupole splitting. However, the thermally induced doublet (DeltaQ = 3.10 mm/sec and delta = 1.28 mm/sec) typical of hydrated forms of reduced (divalent) inorganic iron is not observed in spinach chloroplasts. This doublet is usually associated with degradation of active centers of ferredoxin, a surface-exposed protein of PS I. The Mössbauer spectra of photosynthetic membranes of spinach chloroplasts and cyanobacteria were compared using the probability distribution function of quadrupole shift (1/2 quadrupole splitting DeltaQ) of trivalent iron. The results of calculation of these functions for the two preparations showed that upon increasing the heating temperature there was a decrease in the probability of the presence of native iron-sulfur centers FX, FA, and FB (quadrupole shift range, 0.43-0.67 mm/sec) in heated preparations. This process was also accompanied by an increase in the probability of appearance of clusters of trivalent iron. This increase was found to be either gradual and continuous or abrupt and discrete in photosynthetic membranes of cyanobacteria or spinach chloroplasts, respectively. The probability of the presence of the iron-sulfur centers FX, FA, and FB in chloroplasts abruptly decreases to virtually to zero within the temperature range critical for inhibition of electron transport through PS I to oxygen. In cyanobacteria, both thermal destruction of iron-sulfur centers of PS I and functional degradation of PS I are shifted toward a higher temperature. The results of this study suggest that the same mechanism of thermal destruction of the PS I core occurs in both thermophilic and mesophilic organisms: destruction of iron-sulfur centers FX, FA, and FB, release of oxidized (trivalent) iron, and its accumulation in membrane-bound iron-oxo clusters.

Chloroplasts↗

PubMed2001

Study on conformational changes in hemoglobin protoporphyrin in essential hypertension.

Changes in protoporphyrin conformation, partial pressures of O2 and CO2, and the mechanisms responsible for regulation of pCa and pH in erythrocytes were studied in essential hypertension (EH). Changes in protoporphyrin conformation in EH were accompanied by a decrease in the partial pressure of O2 and an increase in the partial pressure of CO2. This was associated with increased activities of Na+/H+-exchange and Ca2+-dependent K+-channels and with a decreased activity of Ca2+-ATPase. The changes in protoporphyrin conformation in EH are suggested to decrease the efficiency of O2 metabolism in hemoglobin and increase the values of intracellular pCa and pH of erythrocytes.

Calcium-Transporting ATPases↗

PubMed2001

A study of demyelination of nerve fibers using dynamic phase contrast microscopy.

Dynamic phase microscopy was used for evaluation of changes in myelinated axon segment in the paranodal region of nerve fibers during demyelination. Normally paranodal myelin sheath is characterized by regular oscillations of the optical path difference with frequences of 4.2 and 6.7 Hz. Demyelination decreased the amplitude and conduction velocity in nerve fibers and shifted the characteristic frequencies of optical path difference oscillations to 2.8, 3.2, and 11 Hz. These shifts of optical path difference frequencies probably resulted from disturbances in the state of charged phospholipids and a decrease in the level of bound Ca(2+)during demyelination of nerve fiber.

Animals↗

PubMed2000

Photophysical properties of carborane-containing derivatives of 5,10,15,20-tetra(p-aminophenyl)porphyrin.

Absorption, fluorescence emission, fluorescence excitation spectra and fluorescence decay kinetics of carborane derivatives of 5,10,15,20-tetra(p-aminophenyl)porphyrin have been investigated. Carborane derivatives are prepared by acylation of the amino groups of 5,10,15,20-tetra(p-aminophenyl)porphyrin by 9-carboranyl acetyl chloride. From the analysis of the absorption and fluorescence spectra, it is concluded that covalent linking of carborane molecules to the tetraphenylporphyrin molecule significantly changes the self-conjugated pi-system of the porphyrin macrocycle: positions of maxima of absorption and fluorescence spectra shift to the red region by 3-8 nm; the halfwidths of these bands are broadened by 2.5-5.0 nm; the relative intensity of the bands I-IV also changes. The fluorescence decay kinetics of the carborane derivatives are biexponential. According to the experimental data and model simulation, it is concluded that the intramolecular electron transfer proceeds from the porphyrin excited part of the molecule to carboranyls with a rate constant of 415 ps(-1) and efficiency of 0.16-0.8. Recombination of separated charges occurs within 1.4 ns.

Boranes↗

PubMed2000

Dipyridamole and its derivatives modify the kinetics of the electron transport in reaction centers from Rhodobacter sphaeroides.

A well known vasodilator dipyridamole (DIP), 2,6-bis(diethanolamino)-4,8-dipiperidinopyrimido[5,4-d]pyrim idine, and its derivatives have recently been shown as potential co-activators (modulators) in the phenomenon of multidrug resistance (MDR) in cancer therapy. They inhibit the specific function of a transmembrane P-glycoprotein responsible for the ex-flux of anti-cancer drugs from tumor cells. To clarify molecular mechanisms of the anti-MDR activity of DIP and its two derivatives, RA25 and RA47, we have studied their effects on electron transport in reaction centers (RC) from purple photosynthetic bacteria Rb. sphaeroides, using RC as a model system. Increasing concentrations of DIP and RA47 progressively accelerate the back electron transfer from the primary quinone acceptor QA to the bacteriochlorophyll dimer Bchl2 (Bchl2+ -QA- recombination). In the absence of o-phenantroline, when both quinone acceptors QA and QB are involved in the electron transport, RA47 is more effective than DIP. DIP stabilizes the electron on the secondary quinone acceptor QB, the effect manifested as the retardation of Bchl2+ -QB- recombination. Effects of RA25 are negligible in all cases. The drugs are proposed to change the electron transport affecting the RC structural dynamics and the stabilization of the electron on quinone acceptors through modification of H-bonds in the system.

Bacteriochlorophylls↗

PubMed2000

Light-induced processes of cell protection against photodamage.

The processes of light-induced cell protection against photodamage, including DNA photorepair with involvement of photolyases and photoactivation of enzymatic synthesis of photoprotectors and antioxidants (flavonoids, carotenoids, melanins, serotonin, and hemoxygenase), are discussed. Mechanisms of photoprotective effects against photodynamic oxidation of membrane components and photodamage of DNA are analyzed.

Catalysis↗

PubMed2000

Investigation of the electron transfer reactions and redox characteristics of photoactive bacteriochlorophyll in Rhodobacter sphaeroides reaction centers modified by D2O and cryoprotectants.

The effects of D2O, glycerol and dimethyl sulfoxide (DMSO) on redox potential Em of bacteriochlorophyll of a special P2 or [P(M)P(L)] pair, the rate of energy migration from bacteriopheophytin H(M) to [P(M)P(L)], electron transfer from [P(M)P(L)] to bacteriopheophytin H(L) and then to quinone Q(A) in reaction centers (RC) of Rhodobacter sphaeroides were studied. The H2O --> D2O substitution did not change Em of the special pair, whereas addition of 70% glycerol or 35% DMSO (v/v) increased the values of Em by 30 and 45 mV, respectively. Rate constants of energy migration km(H(M)* (km)--> P2), charge separation ke([P(M)P(L)] *H(L) (ke)--> [P(M)P(L)] +H(L)-), electron transfer to quinone kQ did not change after the glycerol addition, whereas isotopic substitution and addition of DMSO caused a 2-3-fold increase in km, ke, and kQ values. Theoretical analysis of the redox center potential dependence on dielectric permeability epsilon, swelling of the protein globule in a solvent, and on changes in the charge distribution (charge shifts) in the protein interior near the redox center was carried out. It has been shown that the H2O replacement with DMSO can result in the Em increase by tens of mV. No correlation was found between the Em values and the rate of charge separation upon isotopic substitution and addition of cryoprotectants. The effect of epsilon of the medium on the rate of electron transport due to changes of energy of intermolecular interaction between the donor and acceptor molecules was estimated.

Bacteriochlorophylls↗

PubMed1999

Inorganic Fe2+ formation upon Fe-S protein thermodestruction in the membranes of thermophilic cyanobacteria: Mössbauer spectroscopy study.

A model description of the Mössbauer spectrum (80 K) of native membranes of the thermophilic cyanobacterium Synechococcus elongatus is suggested on the basis of the known values of quadrupole splitting (deltaE(Q)) and isomer shift (deltaFe) for the iron-containing components of the photosynthetic apparatus. Using this approach, we found that heating the membranes at 70-80 K results in a decrease of doublet amplitudes belonging to F(X), F(A), F(B) and ferredoxin and simultaneous formation of a new doublet with deltaE(Q) = 3.10 mm/s and delta-Fe = 1.28 mm/s, typical of inorganic hydrated forms of Fe2+. The inhibition of electron transfer via photosystem I to oxygen, catalyzed by ferredoxin, occurs within the same range of temperatures. The data demonstrate that the processes of thermoinduced Fe2+ formation and distortions in the photosystem I electron transport in the membranes are interrelated and caused mainly by the degradation of ferredoxin. The possible role of Fe2+ formation in the damage of the photosynthetic apparatus resulting from heating and the action of other extreme factors is discussed.

Bacterial Proteins↗

PubMed1999

Endogenous porphyrin accumulation and photosensitization in the yeast Saccharomyces cerevisiae in the presence of 2,2'-dipyridyl.

The chelator 2,2'-dipyridyl (0.2 mM) induces a remarkable increase of protoporphyrin IX concentration as well as of its Zn-containing complex in the yeast Saccharomyces cerevisiae. Endogenous porphyrin accumulation results in five- to six-fold cell sensitization to visible light (400-600 nm). Mitochondria isolated from the cells grown in the presence of 2,2'-dipyridyl accumulate protoporphyrin IX and Zn-protoporphyrin IX, while plasma membranes besides that exhibit porphyrin-type fluorescence at 670-675 nm in chloroform extract. The protoporphyrin IX content increases more than four-fold in mitochondria and two-fold in plasma membranes isolated from chelator-treated cells. The relative contribution of subcellular structure photodestruction to photoinduced cell inactivation is discussed.

2,2'-Dipyridyl↗

PubMed1999

[The use of microfluorimetric analysis for the studies of the influence of changed gravity on isolated lymphocytes in the spleen of the mouse].

Effects of simulated changed gravity on isolated splenetic lymphocytes of mouse were evaluated with the microfluorimetic technique enabling observation of probe fluorescence in individual cells. It was stated that 5 and 60 min of clinostatting stimulated fluorochrome accumulation in cells whereas centrifugation, particularly for 60-minutes, decreased the ability of cells to accumulate fluorescein. Also, alteration of the gravity force had the opposite effect on the ability of cells to retain fluorescein. The most significant drain of the dye immediately after short hypogravity may be indicative of the functional lability of cells during clinostatting. However, as judged by slight changes in intracellular pH, metabolic and regulatory functions were not affected. Hypergravity for 15 min decreased intracellular pH. The increased period of centrifugation stabilized the parameter. Absence of changes in the proliferative activity in all the test exposures also backs up the conclusion that short-term changes in gravity do not produce any substantial shifts in the morphofunctional state of cells in vitro.

Animals↗

PubMed1998

The cytochrome subunit structure in the photosynthetic reaction center of Chromatium minutissimum.

Gel-electrophoretic assay revealed that the photosynthetic reaction center (RC) of Chromatium minutissimum, in contrast to the well-known RC Rhodopseudomonas viridis, consists of five rather than four subunits with molecular masses of 37, 34, 25, 19, and 17 kDa. The 37- and 19-kDa subunits are stained with tetramethylbenzidine for the cytochrome c hemes. Absorption spectra show that the concentration of reduced cytochromes in the C. minutissimum RC poised at redox potential of -150 mV (fully reduced pool of hemes) is about three times more than in the C. minutissimum RC poised at redox potential of +260 mV (only high-potential hemes are reduced). The results of redox titration of absorption changes at the cytochrome c alpha-band are most appropriately approximated by a six-component theoretical curve with the midpoint potentials of Em1 = 390 mV, Em2 = 320 mV, Em3 = 210 mV, Em4 = 100 mV, Em5 = 20 mV, and Em6 = -50 mV. Possible functions of the cytochromes with the midpoint potentials 210 and 100 mV, which have not been found in purple bacteria before, are discussed.

Chromatium↗

PubMed1998

Effect of deuteration and cryosolvents on the energy transduction in primary processes of photosynthesis.

Effects of cryosolvents and D2O/H2O substitution on the reaction centres (RCs) isolated from photosynthetic bacteria were studied with respect to the role of intra-protein hydrogen bonds in the primary photosynthetic electron transfer. As a result of such treatment of RCs, the charge separation rate between the photoactive bacteriochlorophyll (P2 dimer) and bacteriopheophytin and the rate of electron transfer to the primary quinone slowed down. The energy migration rate from bacteriopheophytin (BPheM), inactive in electron transport, to P2 decreased as well. Although cryosolvents can shift the redox potential of the photoactive pigment, there is no direct correlation between the P2 potential and the effects of these modifying agents on the photosynthetic process in RCs occurring with participation of P2. The removal of H subunit from the pigment-protein complex results in the pronounced weakening of the dimethyl sulfoxide modifying effects on the RC hydrogen bonds. The role of structural and dynamic state in the functioning of the photosynthetic bacterial RCs is analyzed. Relaxation processes in purple bacteria RCs accompanying the primary picosecond steps of energy transformation proceed with the participation of small proton-containing molecular groups in the immediate surroundings of electron transfer carriers. In this paper, we present results concerning mechanisms of primary photosynthetic steps, which were initiated by A. A. Krasnovsky and have been studied for several years at the Department of Biophysics. This paper is dedicated to the memory of our teacher Prof. A. A. Krasnovsky.

Bacteriochlorophylls↗

PubMed1998

The influence of short term gravity changes on mouse spleen lymphocytes in vitro (microfluorimetry with probes).

Despite of the great successes achieved in gravitational cell biology, problem of mechanisms underlying cell effects of gravity is far from being solved. Available data are very contradictory, because of the differences in experimental conditions: gravity value, exposition time, type of cells and other factors. Besides, there are no satisfactory methods to avoid additional influence of various biologically active factors on cells during the space experiments. It is absolutely clear, that successful development in this field may be provided only by investigations in controlled experimental conditions, including analysis of cell functional activity and state of cell regulatory systems. One of the most adequate approaches for these scientific tasks is cell microfluorimetry with using of fluorescent probes. The study of influence of short-term pattern changes in gravity (clinostation and centrifugation) on hydrolytic activity of intracellular content of mouse spleen lymphocytes, leakage of accumulated fluoresce in and intracellular pH is the goal of present research.

Animals↗

PubMed1998

[Effect of mild-frequency ultraviolet radiation on mice splenic lymphocytes].

Investigation of the action of mid-frequency ultraviolet radiation (302 nm) on isolated lymphocytes of mice spleen pointed out that intracellular pH of lymphocytes starts decreasing from 0.3 J/cm2. Dose rise above 2.5 J/cm2 increases the number of cells with damaged plasmatic membrane within the lymphocyte population and aggravates the ability of cells to accumulate fluorescein fluorochrome as a product of intracellular fluorescein diacetate hydrolysis.

Animals↗