Biomedical subjects

A B Rubin

Publications and source records attributed to A B Rubin.

At least 19 recordsLinked to original sources

PubMed2006

Direct simulation of plastocyanin and cytochrome f interactions in solution.

Most biological functions, including photosynthetic activity, are mediated by protein interactions. The proteins plastocyanin and cytochrome f are reaction partners in a photosynthetic electron transport chain. We designed a 3D computer simulation model of diffusion and interaction of spinach plastocyanin and turnip cytochrome f in solution. It is the first step in simulating the electron transfer from cytochrome f to photosystem 1 in the lumen of thylakoid. The model is multiparticle and it can describe the interaction of several hundreds of proteins. In our model the interacting proteins are represented as rigid bodies with spatial fixed charges. Translational and rotational motion of proteins is the result of the effect of stochastic Brownian force and electrostatic force. The Poisson-Boltzmann formalism is used to determine the electrostatic potential field generated around the proteins. Using this model we studied the kinetic characteristics of plastocyanin-cytochrome f complex formation for plastocyanin mutants at pH 7 and a variety of ionic strength values.

Computer Simulation↗

PubMed2005

Role of viscosity and permeability of the erythrocyte plasma membrane in changes in oxygen-binding properties of hemoglobin during diabetes mellitus.

Changes in viscosity and permeability of the plasma membrane and conformation of erythrocyte hemoglobin hematoporphyrin were found in patients with diabetes mellitus. The decrease in oxygen binding and increase in deoxyhemoglobin concentration during diabetes mellitus were accompanied by changes in viscosity and permeability of the membrane for Na+, H+, Ca2+, and K+. Our results suggest that oxygen-binding properties of hemoglobin depend on viscosity and permeability of the erythrocyte plasma membrane.

Calcium↗

PubMed2005

Erythrocyte membrane fluidity and haemoglobin haemoporphyrin conformation: features revealed in patients with heart failure.

This study examined the possible involvement of abnormal erythrocyte oxygen (O(2)) transport in the pathogenesis of heart failure. Haemoglobin (Hb) haemoporphyrin conformation was assessed by Raman spectroscopy (RS) of blood samples, whereas membrane fluidity was estimated at depths of 0.6-0.8 and 2.2nm by electron-paramagnetic resonance spectroscopy of erythrocytes loaded with spin-labeled 5-doxylstearic acid and 16-doxylstearic acid, respectively. The fluidity of erythrocyte membranes from patients with heart failure was decreased in the area near the membrane surface and remained unchanged in the deeper hydrophobic membrane regions. The same differences were also detected in healthy controls subjected to chronic high-altitude hypoxia. RS demonstrated that in heart failure the total content of Hb-ligand complexes and the relative content of Hb-nitric oxide (NO) complexes with cleaved Fe(2+)-globin bond was decreased, whereas content of Hb-NO complexes with preserved Fe(2+)-globin bond was increased. We propose that this phenomenon contributes to the reduced O(2) tissue supply seen in patients with heart failure.

Journal Article↗

PubMed2005

[The role of plasmatic erythrocytic membrane in formation of hypoxia in patients with chronic cardiac failure].

AIM: To study oxygen supply to erythrocytes in patients with chronic cardiac failure as a factor provoking hypoxia. MATERIAL AND METHODS: The trial enrolled 12 men with chronic cardiac failure (CCF) of functional NYHA class II aged 37 to 74 years (group A). Group B--healthy donors (n = 10) aged 20-40 years. Conformation changes of hemoporphirine were detected with degradation spectroscopy, viscosity of plasmatic membrane--with resonance spectroscopy. Degradation spectroscopy estimated content of Hb-ligant complexes as 0.34 +/- 0.013; complexes I Hb-NO 0.73 +/- 0.11, complexes II Hb-NO 0.28 +/- 0.08 (group A). RESULTS: Electronic-paramagnetic spectroscopy has estimated: S--0.716 +/- 0.005 (group A), 0.667 +/- 0.011 (group B). In group B- 0.5 +/- 0.08; 0.41 +/- 0.22; 0.55 +/- 0.12, respectively. CONCLUSION: Patients with CHF have high microviscosity of plasmatic erythrocytic membrane near location of polar lipid groups; subnormal content of oxyhemoglobin and elevation of the number of complexes of nitric hemoglobin-oxide; altered binding of nitric oxide with hemoglobin.

Adult↗

PubMed2004

Effect of a single excitation stimulus on photosynthetic activity and light-dependent pH banding in Chara cells.

Using pH microelectrodes and a Microscopy PAM (pulse-amplitude modulated) chlorophyll fluorometer, it is shown that a propagation of an action potential in Chara corallina leads to transient suppression of spatially periodic pH profiles along the illuminated cell. The suppression was manifested as a large pH decrease in the alkaline zones and a slight pH increase in the acid zones. The propagating action potential diminished the maximum yield of chlorophyll fluorescence (F(m)') in the alkaline cell regions, as well as the quantum yield of photosystem II photochemistry, without affecting F(m)' in the acid cell regions. The results indicate an interference of membrane excitation in the mechanisms responsible for pH banding patterns in Characean algae. Apparently, the electrical excitation of the plasma membrane in the alkaline cell regions initiates a pathway that can modulate membrane events at the thylakoid membrane.

Action Potentials↗

PubMed2004

Effect of low temperatures on photochemical activity of PS1 reaction centers from Synechocystis sp. frozen under illumination.

After cooling of Synechocystis sp. photosystem 1 (PS1) reaction centers (RC) to 160 K under illumination most of the photoactive pigment is fixed for a long time in the oxidized state. The same effect is observed in purple bacteria RC. The dark reduction kinetics of PS1 P700 chlorophyll, which still retains its photochemical activity, in these samples was similar to that in samples cooled in the dark. We suggest that the photoinduced charge separation in PS1 RC, as well as in purple bacteria RC, is accompanied by conformational changes that can be fixed in samples cooled under illumination. As a result, the electrons photomobilized in RC cooled under illumination are unable to return backward the process of electron transfer to P700(+) after cessation of actinic illumination. Such irreversible trapping of electrons can take place in different parts of the PS1 RC electron acceptor chain.

Cold Temperature↗

PubMed2004

Apoptosis in serum-deprived vascular smooth muscle cells: evidence for cell volume-independent mechanism.

Shrinkage is the earliest hallmark of cells undergoing apoptosis. This study examines the role of this phenomenon in the onset of vascular smooth muscle cell (VSMC) apoptosis triggered by growth factor withdrawal. In hyperosmotic media, VSMC showed the same amplitude of shrinkage but were more resistant to apoptosis than endothelial, epithelial and immune system cells. As with growth factor withdrawal, apoptosis in hyperosmotically-shrunken VSMC was sharply potentiated by transfection with E1A-adenoviral protein and was suppressed by activation of cAMP signaling as well as by the pan-caspase inhibitor z-VAD.fmk. Both cell shrinkage and apoptosis in VSMC-E1A treated with hyperosmotic medium were potentiated under sustained Na+, K+ pump inhibition with ouabain that was in contrast to inhibition of apoptosis documented in ouabain-treated, serum-deprived cells. After 1-hr incubation in serum-deprived medium, VSMC-E1A volume declined by approximately 15%. Transfer from hypotonic to control medium decreased VSMC-E1A volume by approximately 25% without any induction of apoptosis. Neither swelling in hyposmotic medium nor dissipation of the transmembrane gradient of K+ and major organic osmolytes protected serum-deprived VSMC-E1A from apoptosis. Thus, our results show that similarly to immune system, endothelial and epithelial cells, extensive VSMC shrinkage in hyperosmotic medium leads to the development of apoptosis. In contrast to hyperosmotic medium, the modest cell volume decrease occurring in serum-deprived VSMC does not contribute to triggering of the apoptotic machinery.

Adenoviridae↗

PubMed2004

Effect of oxygen on temporary stabilization of photoreduced quinone acceptors in Rhodobacter sphaeroides reaction centers.

The effect of molecular oxygen on the photochemical activity of the Rhodobacter sphaeroides reaction centers frozen to 160 K under actinic illumination was investigated by the ESR method. About 90% of initially photochemically active bacteriochlorophyll (P) were fixed at 160 K for a long time in aerobic samples in an inactive form. In anaerobic samples, not more than 65% were fixed in an inactive form under the same conditions. In aerobic preparations, a small portion of photochemically active bacteriochlorophyll (about 10%) that retains its photochemical activity at 160 K after freezing under illumination has dark reduction kinetics similar to that of samples at room temperature after several seconds of actinic illumination. In anaerobic samples frozen under illumination, the remaining photochemically active reaction centers (35%) have the same dark reduction kinetics as samples illuminated at 295 K for 1-2 min. The conclusion is that the irreversible stabilization of bacteriochlorophyll P in the oxidized inactive state formed in the reaction centers frozen under illumination is brought about by light-induced conformational changes fixed under low temperatures.

Bacterial Chromatophores↗

PubMed2004

Investigation of erythrocyte shape, plasma membrane fluidity and conformation of haemoglobin haemoporphyrin under the influence of long-term space flight.

The investigation of long-term space flight (SF) effect on the blood cells function is of great importance for modern space biology and medicine. We established that the number of discocytes decreased in the period of early rehabilitation after long-term SF. After SF plasma membrane fluidity and phospholipid content decreased and cholesterol content increased. After SF the amount of haemoglobin decreased and the parameters characterizing haemoglobin haemoporyphyrin (HH) conformation changed. We suppose that erythrocyte shape, membrane fluidity and HH conformation are among factors affecting oxygen transfer during and after space flight.

Cholesterol↗

PubMed2003

The dependence of algal H2 production on Photosystem II and O2 consumption activities in sulfur-deprived Chlamydomonas reinhardtii cells.

Chlamydomonas reinhardtii cultures, deprived of inorganic sulfur, undergo dramatic changes during adaptation to the nutrient stress [Biotechnol. Bioeng. 78 (2002) 731]. When the capacity for Photosystem II (PSII) O(2) evolution decreases below that of respiration, the culture becomes anaerobic [Plant Physiol. 122 (2000) 127]. We demonstrate that (a) the photochemical activity of PSII, monitored by in situ fluorescence, also decreases slowly during the aerobic period; (b) at the exact time of anaerobiosis, the remaining PSII activity is rapidly down regulated; and (c) electron transfer from PSII to PSI abruptly decreases at that point. Shortly thereafter, the PSII photochemical activity is partially restored, and H(2) production starts. Hydrogen production, which lasts for 3-4 days, is catalyzed by an anaerobically induced, reversible hydrogenase. While most of the reductants used directly for H(2) gas photoproduction come from water, the remaining electrons must come from endogenous substrate degradation through the NAD(P)H plastoquinone (PQ) oxido-reductase pathway. We propose that the induced hydrogenase activity provides a sink for electrons in the absence of other alternative pathways, and its operation allows the partial oxidation of intermediate photosynthetic carriers, including the PQ pool, between PSII and PSI. We conclude that the reduced state of this pool, which controls PSII photochemical activity, is one of the main factors regulating H(2) production under sulfur-deprived conditions. Residual O(2) evolved under these conditions is probably consumed mostly by the aerobic oxidation of storage products linked to mitochondrial respiratory processes involving both the cytochrome oxidase and the alternative oxidase. These functions maintain the intracellular anaerobic conditions required to keep the hydrogenase enzyme in the active, induced form.

Animals↗

PubMed2003

Transitions from alkaline spots to regular bands during pH pattern formation at the plasmalemma of Chara cells.

A scanning pH-microprobe was used to study pH patterns near the surface of Chara corallina cells at various light intensities and during light-induced transitions from homogeneous pH distribution to alternating pH bands. In the irradiance (PAR) range 4-400 micromol quanta m(-2) s(-1), the sustained pH profiles consisted of alternating acid and alkaline bands with a characteristic length of 7-10 mm and pH shifts as large as 2-3 units. At lower irradiance, the number of alkaline bands decreased while the amplitude of remaining peaks stayed high. On cyclic changes in light intensity, a hysteresis of pH banding was observed: the pH bands tolerated low irradiance in weakening light, but higher irradiance was required for their emergence after dark adaptation of the cell. The pH profiles measured for different paths of electrode scanning suggest that the pH pattern at low light level represents patches coexisting with bands. The exposure of the cell to high-intensity light led to formation of radially symmetrical bands. Transformations of the pH pattern induced by lowering the light intensity were similar to those induced by transcellular electric current (1.5-3 microA). The data suggest that band formation at the plasmalemma of Chara cells proceeds through the initial appearance of multiple patches with a localized H(+)-transporting activity and subsequent spot rearrangements (fusion, deletions, widening), leading to establishment of alternating bands.

Adaptation, Physiological↗

PubMed2003

[Effect of short-term hypoxia and re-oxygenation on mice peritoneal macrophages in vitro].

Microfluorimetry of single cells could help to analyze their morphology and function state during changes of gas environment. It is very important to have a possibility of the cell visual control during hypoxia and collection of dynamic fluorimetric data in digital form. The effects of short-term pO2 decrease were studied. For estimating the effects of hypoxia and reoxygenation we used the mice peritoneal macrophages, which are very sensitive to physical, chemical and regulatory stimuli. A special small chamber for fluorimetric measurements during pO2 changes, was developed. The level of active oxygen forms, intracellular pH, and cell membrane instability were investigated during replacement of air by nitrogen or argon (of the basal level decreased to 20% of basic level) and in subsequent reoxygenation. The increase of active oxygen forms was shown during 30 min of hypoxia and their level continued to rise immediately after reoxygenation. A short-term decrease and subsequent increase of pO2 in the medium led to an increase of intracellular pH level. The shifts of measured cell indices were stabilized after 30-40 min of pO2 changes thus suggesting a fast comprehension of countermeasure cell mechanisms. No macrophages with membrane disorders were found despite the rise of the active oxygen forms level during hypoxia and reoxygenation in vitro. There were no significant differences between nitrogen and argon used for replacement of air in the medium. The data obtained suggest a high resistance of macrophages against pO2 changes and an involvement of the antioxidative mechanisms for cell protection especially during reoxygenation period.

Animals↗

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↗