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Biomedical subjects

A B Rubin

Publications and source records attributed to A B Rubin.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1997

Nuclear targeting of chlorin e6 enhances its photosensitizing activity.

Although photosensitizers, molecules that produce active oxygen species upon activation by visible light, are being extensively used in photodynamic therapy to treat cancer and other clinical conditions, problems include normal cell and tissue damage and associated side effects, which are attributable in part to the fact that cytotoxic effects are largely restricted to the plasma membrane. We have previously shown that the photosensitizer chlorin e6 has significantly higher photosensitizing activity when present in conjugates containing specific ligands and thus able to be internalized by receptor-expressing cells. In this study we use insulin-containing conjugates to which variants of the simian virus SV40 large tumor antigen nuclear localization signal (NLS) were linked to target chlorin e6 to the nucleus, a hypersensitive site for active oxygen species-induced damage. NLSs were either included as peptides cross-linked to the carrier bovine serum albumin or encoded within the sequence of a beta-galactosidase fusion protein carrier. The results for photosensitization demonstrate clearly for the first time that NLSs increase the photosensitizing activity of chlorin e6, maximally reducing the EC50 by a factor of over 2000-fold. This has wide-reaching implications for achieving efficient cell type-specific photodynamic therapy.

Amino Acid Sequence↗
PubMed1997

Effect of hydration on the structure, dynamics and function of photosynthetic membranes of purple bacteria.

NMR spectra and relaxation times T1 and T2 for 31P in membranes of Rhodobacter sphaeroides were investigated at different relative humidity levels. The results are compared to the hydration curves, fatty acid composition and the structure-dynamic and functional characteristics of the membranes of photosynthetic bacteria Rb. sphaeroides, Rhodospirillum rubrum and Ectothiorhodospira shaposhnikovii. The differences in the state of lipid phase of these membranes are revealed under low humidity, and this is conducive to variability of their structural dynamic and functional characteristics during the hydration process. Based on the results obtained and the data on model systems, four stages of hydration process are distinguished with different effects on the structure and dynamics of membrane components. These stages are: hydration of a portion of polar groups, involvement of water molecules in the hydrogen bonds within macromolecules and the lipid phase, hydration of all polar groups with the appearance of water with high dielectric constant thus making possible the lateral diffusion within the membrane and realization, through water participation, of conditions within organelles and cells required for the process regulation at these levels. The mechanism of water action on various membrane components and their dynamics at each stage are discussed, as well as the effect of different types of motion on the efficiency and regulation of electron transport in the photosynthetic chain of the membranes studied.

Cell Membrane↗
PubMed1996

The role of membrane-bound porphyrin-type compound as endogenous sensitizer in photodynamic damage to yeast plasma membranes.

The effect of visible light (400-600 nm) on Candida guilliermondii and Saccharomyces cerevisiae was studied, and irradiation fluences killing the yeast cells without exogenous sensitizers were determined. The lethal effects are strongly oxygen-dependent, suggesting the involvement of photodynamic reactions mediated by endogenous sensitizer(s). Repair-deficient strains of S. cerevisiae show the same photosensitivity as the wild-type strain indicating that visible light does not photosensitize repairable DNA lesions. As was demonstrated using the microfluorometric method with the fluorochrome primulin, photodestruction of plasma membrane permeability barriers is important for yeast cell lethality. Visible light at cell-killing fluences induces lipid peroxidation in plasma membrane ghosts isolated from C. guilliermondii. Data obtained suggest the important role of singlet oxygen photogenerated by endogenous sensitizer(s) in initiating oxidative reactions. A spectrofluorometric analysis of the plasma membrane ghosts revealed one compound fluorescent in the visible spectral region at 683 nm. Its fluorescence excitation and absorption spectra have structures typical for porphyrins. The plasma membrane-bound porphyrin-like compound is different in some fluorescence properties from mitochondrial porphyrins. Estimation of its amount gives a value of 0.1 nmol porphyrin per milligram of protein of the plasma membrane ghosts. This porphyrin-type compound is considered to be the most probable candidate for the role of the sensitizer in photodynamic damage to yeast plasma membrane and cell inactivation by visible light.

Candida↗
PubMed1995

High-specific binding of Fe(II) at the Mn-binding site in Mn-depleted PSII membranes from spinach.

The interaction of Fe(II) and Fe(III) with the 'high-affinity Mn-binding site' in Mn-depleted photosystem II (PSII) was investigated using diphenilcarbazide (DPC)/2,6-dichlorophenol-indophenol (DCIP) inhibition assay. Fe(III) was ineffective in the inhibition of DPC-DCIP reaction while Fe(II) decreased the rate of DCIP photoreduction supported by DPC in the same concentration range as Mn(II). The effectivity of the interaction of Fe(II) with the high affinity Mn-binding site depends on different anions in the same manner as for Mn(II) and coincides with hierarchy observed for the stimulation of O2 evolution. The Fe(II) binding is accompanied by its oxidation. By using reductants it was shown that the high affinity site contains a redox-active component and the reduction of this component totally prevents the binding of Fe(II).

2,6-Dichloroindophenol↗
PubMed1992

Thermally-induced delayed fluorescence of photosystem I and II chlorophyll in thermophilic cyanobacterium Synechococcus elongatus.

Stationary delayed fluorescence (DF) of chlorophyll in isolated membrane preparations from thermophilic cyanobacterium Synechococcus elongatus was investigated as a function of temperature. Two peaks at different temperatures were observed. The low-temperature peak (54-60 degrees C) coincided with the main maximum of the thermally-induced delayed fluorescence of chlorophyll in intact cells and PSII-particles with active oxygen-evolving system. The high-temperature peak (78 degrees C) coincided with the minor band of delayed light emitted by intact cells. It was also observed in the delayed fluorescence emission from a PSI-enriched fraction preparation. The intensities of the DF peaks were dependent on the presence of inhibitors, donors and acceptors that cause specific effects on electron transport of the two photosystems. The low-temperature and high-temperature peaks were related to PSII and PSI, respectively. The manifestation of delayed fluorescence from PSI and PSII at different temperatures seems to be a specific property of thermophilic cyanobacteria. The reason for this may be a high thermal stability of the photosystems and the lack of the PSII antenna complex in isolated membranes. Consequently, the relative yield of delayed fluorescence from PSI markedly increases. Thermally-induced fluorescence seen in membranes of cyanobacteria showed a high sensitivity to structural and functional membrane alterations induced by pH changes, different electron transport stabilizing agents or different concentrations of MgCl2.

Chlorophyll↗