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Biomedical subjects

A B Rubin

Publications and source records attributed to A B Rubin.

At least 55 records · Page 3Linked to original sources
PubMed1990

Thermal stability of electron transport in PS II membranes and particles from the thermophilic cyanobacteria.

Thermal stability of the ferricyanide (FC) and dichlorophenolindophenol (DCIP) reducing reactions was investigated in isolated membrane preparations and PS II particles with active water splitting system from the cyanobacterium Synechococcus elongatus. In a hypotonic medium, the thermostability was seen to be much higher for the DCIP than for the FC reduction reaction. After the addition of high concentrations of polyethylene glycol (Mwt = 4000) or sodium citrate to the medium, the FC reduction reaction appeared to be more temperature resistant. Data on the effects of temperature, DCMU and detergents on the electron transfer rate in PS II provide evidence suggesting that the different thermal stabilities of the two reactions are due to different physico-chemical properties of the electron donor sites to FC and DCIP. The data suggest that regions of contact between individual macromolecular complexes of the electron transport chain are the most labile sites of the photosynthetic apparatus. The role of the composition and properties of the intracellular medium on thermostability are emphasized.

2,6-Dichloroindophenol↗
PubMed1990

Tetracaine inhibition of electron transport in pea chloroplasts is coupled to calcium displacement by the local anesthetic.

Chloroplasts isolated from pea seadlings grown on water containing 45Ca2+ were treated with local anesthetic tetracaine. Addition of tetracaine inactivated the electron transport activity of donor side photosystem II. This inhibition was accompanied by 45Ca2+ release from the chloroplast membranes as the whole and destroyed by osmotic shock. No such effect was observed when Tris or hydroxylamine were used to inhibit the donor side photosystem II. Upon thermal inactivation of chloroplasts 45Ca2+ release occurred but at temperatures above 80 degrees. The functional role of Ca2+ in photosystem II is discussed.

Calcium↗
PubMed1989

Near-UV activation of enzymatic conversion of 5-hydroxytryptophan to serotonin.

Near-UV (337 nm) photoactivation of the 5-hydroxytryptophan decarboxylation reaction producing serotonin has been observed. The photoactivation effect was investigated as a function of fluence rate and fluence, and pH. Photoactivation of decarboxylase activity was found to occur at nearly neutral pH values (low activity of the enzyme in the dark). The findings indicate that the effect of light is similar to a pH shift toward the acid region, which causes the enzyme conversion from the inactive to active form. Pyridoxal phosphate, the decarboxylase cofactor, in the form of an adduct absorbing at 330-340 nm, is suggested as a candidate for the role of the photoactive chromophore of decarboxylase.

5-Hydroxytryptophan↗
PubMed1989

[Molecular mechanisms of the action of local anesthetics].

Raman spectroscopy revealed a suppression of the polyene chain of C40-carotenoids in membrane of the frog nerve during local action of an anesthetic agent in resting and excitation. The phosphatidylcholine binding decreased during rhythmic excitation and local anesthetic action. A mechanism of potential-dependent changes of the carotenoid conformation during local anesthetic action, was discussed.

Action Potentials↗
PubMed1988

Spectral, Photophysical, and Stability Properties of Isolated Photosystem II Reaction Center.

Photosystem II reaction center (RC) preparations isolated from spinach (Spinacea oleracea) by the Nanba-Satoh procedure (O Nanba, K Satoh 1987 Proc Natl Acad Sci USA 84: 109-112) are quite labile, even at 4 degrees C in the dark. Simple spectroscopic criteria were developed to characterize the native state of the material. Degradation of the RC results in (a) blue-shifting of the red-most absorption maximum, (b) a shift of the 77 K fluorescence maximum from approximately 682 nm to approximately 670 nm, and (c) a shift of fluorescence lifetime components from 1.3-4 nanoseconds and >25 nanoseconds to approximately 6-7 nanoseconds. Fluorescence properties at 77 K seem to be a more sensitive spectral indicator of the integrity of the material. The >25 nanosecond lifetime component is assigned to P680(+) Pheophytin(-) recombination luminescence, which suggests a correlation between the observed spectral shifts and the photochemical competence of the preparation. Substitution of lauryl maltoside for Triton X-100 immediately after RC isolation stabilizes the RCs and suggests that Triton may be responsible for the instability.

Journal Article↗
PubMed1984

Permeability of bilayer lipid membranes for superoxide (O2-.) radicals.

Egg yolk phosphatidylcholine monolamellar liposomes (1000 A in diameter) loaded with cytochrome c were placed into an external solution, in which superoxide radicals, O2-., were generated by a xanthine-xanthine oxidase system. The penetration of the superoxide radicals across the liposomal membrane was detected by cytochrome c reduction in the inner liposome compartment. The effects of modifiers and temperature on this process were studied. The permeability of liposomal membrane for O2-. (P'O-2 = (7.6 +/- 0.3) X 10(-8) cm/s), or HO.2 (P'HO.2 = 4.9 X 10(-4) cm/s) were determined. The effect of the transmembrane electric potential (K+ concentration gradient, valinomycin) on the permeability of liposomal membranes for O2-. were investigated. It was found that O2-. can penetrate across liposomal membrane in an uncharged form. The feasibility of penetration of superoxide radicals through liposomal membrane, predominantly via anionic channels, was demonstrated by the use of an intramolecular cholesterol-amphotericin B complex.

Amphotericin B↗
PubMed1984

[Permeability of bilayer phospholipid membranes to superoxide oxygen radicals].

Lecithin monolayer liposomes (1000 A in diameter) loaded with cytochrome c were placed into the external solution, in which O2 superoxide radicals were regenerated by the xanthine-xanthine oxidase system. The penetration of superoxide radicals across the liposomal membranes was followed by cytochrome c reduction in the interval volume of the liposomes. The effects of lipid membrane modifiers and temperature on this process were investigated. The results obtained were used for calculation of the permeability coefficients of bilayer lipid membranes for O(2) (P'O(2) = (7.6 +/- 0.3) . 10(-8) cm . s-1) or HO . 2(P'HO(2) = 4.9 x 10(-4) cm . s-1). The effect of the transmembrane electric potential (concentration gradient of H+, valinomycin) on the permeability of liposomal membranes for the superoxide radical was studied. The superoxide radical was down to penetrate across the bilayer lipid membranes in an unloaded state. Using an intramolecular cholesterol-amphotericin B-complex, the superoxide radicals were shown to penetrate across the bilayer lipid membranes, predominantly via the anionic channels.

Amphotericin B↗
PubMed1982

Mössbauer spectroscopy of iron metabolism and iron intracellular distribution in liver of rats.

Mössbauer spectroscopy was used to investigate the distribution of iron in rat organs and its localisation in liver subcellular fraction. A 57Fe-sucrose complex solution was injected by 0.5 ml doses into tail veins of animals every day, during a 6-day period. Mössbauer spectra were measured in spleen, blood, liver and liver subcellular fractions. The mössbauer spectrum of a spleen sample has two symmetrical doublets, one with delta = 0.6 mm/s and delta = 0.7 mm/s, and the other with delta = 1.0 mm/s and delta = 2.35 mm/s. The Mössbauer spectrum of blood has parameters which are close to those for carboxyhemoglobin and oxyhemoglobin complexes. After the addition of sodium citrate, the proportion of the carboxyhemoglobin complex increases. The Mössbauer spectrum of liver has a two-component pattern with two symmetrical doublets, the first with delta = 0.6 mm/s and delta = 0.63 mm/s and the second with delta = 1.4 mm/s and delta = 3.45 mm/s. The first component, which was identified as ferritin, is present in all subcellular fractions (800 x gav sediment fraction, mitochondrial/lysosomal, microsomal and supernatant fractions), with its greatest content in microsomal fraction. After the addition of NaBH4 to mitochondrial/lysosomal fraction, about 20% of the iron contained in ferritin was reduced. In the Mössbauer spectrum this is reflected by an appearance of a doublet with delta = 0.85 mm/s and delta = 3.7 mm/s.

Animals↗
PubMed1982

[Reconstitution of the function of the coupling complex of chloroplasts on phospholipid vesicles].

The function of H+-ATPase (CF1-CF0) complex from spinach chloroplasts was reconstituted on azolectin liposomes. Using these proteoliposomes, the 32P-ATP exchange reaction sensitive to dicyclohexylcarbodiimide and uncouplers was established. Combined incorporation of H+-ATPase and bacteriorhodopsin as a delta mu H+ inducer results in photophosphorylation. The optimal conditions for production of liposomes with a low permeability of membranes for ions were elaborated with a view towards improving the existing reconstitution methods.

Adenosine Triphosphatases↗
PubMed1981

Fast stages of photoelectric processes in biological membranes. III. Bacterial photosynthetic redox system.

Chromatophores of photosynthetic bacteria Rhodospirillum rubrum, Rhodopseudomonas sphaeroides and Chromatium minutissimum were associated with a collodion film impregnated with a decane solution of asolectin. A very short light flash inducing a single turnover of the chromatophore photosynthetic redox system was found to induce the formation of an electrical potential difference amounting to 60 mV, directed across the film as measured with an orthodox electrometer technique. The main phase of the photoelectric response had a tau value of less than 200 ns. Addition of menadione and some other redox mediators increases the main phase amplitude and induces a slower phase (tau = 200 microseconds). In Ch. minutissimum chromatophores that retained their endogenous cytochrome c pool, one more electrogenic phase was revealed (tau = 20 microseconds). Redox titrations of the electric response and bacteriochlorophyll absorption at 430 nm as well as measurements of the kinetics of cytochrome c oxidation have indicated that the fastest electrogenic phase is due to electron transfer from bacteriochlorophyll to Fe-ubiquinone, the 20-microseconds phase to cytochrome c2+ - bacteriochlorophyll+ oxidoreduction, and the 200-microseconds phase to Fe-ubiquinone- oxidation by a secondary quinone. In the decay of the photoelectric response, a 30-ms phase was identified which was explained by a reverse electron transfer from reduced Fe-ubiquinone to oxidated bacteriochlorophyll. The difference in the fast kinetics of photoelectric generation by the bacteriochlorophyll system from those by bacterial and animal rhodopsins has been discussed.

Ascorbic Acid↗
PubMed1981

[Light-induced generation of membrane potential in intact chloroplasts suspended in H2O or D2O media].

The membrane potential changes induced by short flashes and continuous light were investigated in isolated chloroplasts of Peperomia metallica suspended in H2O- or D2O media. The potential generated in H2O-suspended chloroplasts by a single turnover flash is approximately two times lower than the maximal level of potential induced by continuous light. The photoelectric response of D2O-suspended chloroplasts differs from that of H2O-suspended chloroplasts by an increased amplitude and a prolonged phase of the potential rise. Te dark decay of the potential proceeds 2-3 times slower in the D2O-suspended chloroplasts as compared to the H2O-suspended chloroplasts. The magnitude of the flash-induced potential is somewhat lower for the chloroplasts in D2O than for the chloroplasts in the H2O medium. The results obtained suggest that the substitution of H2O for D2O results in a decrease of the ionic conductance and an increase of stability of thylakoid membranes. It was shown that the rise of electrical potential under continuous illumination proceeds in two stages. The difference kinetics of membrane potential changes are observed under conditions of separate activity of two systems of photosynthesis.

Chloroplasts↗
PubMed1981

[Structural-functional characteristics of photosynthetic reaction centers extracted by treatment with lauryldimethylamine oxide from Rhodopseudomonas sphaeroides (wild type)].

A method for isolation of photoactive reaction centers from Rps. sphaeroides (wild type) chromatophores, using lauryldimethylamine oxide (LDAO) as detergent, is described. The preparation obtained is free of a light-harvesting pigment-protein complex and cytochromes. A high degree of purity can be demonstrated from the adsorption indexes of the preparation equal to A280 : A800 = 1.2--1.3; A760 : A800 : A870 = 1 : 2 : 0.9. Data from polyacrylamide gel electrophoresis suggest that the integral protein component of the preparation is made up of three polypeptides with molecular weights of 30 000, 24 000 and 20 000. Under continuous illumination the preparation exhibits an effective electron transfer from the bacteriochlorophyll dimer (BChl)2 to a system of quinone acceptors (X1, X2). The ambient potential Em of (BChl)2 half-recovery was estimated as + 475 mV and pH 7.2. The rate constant for direct electron transfer from X1- to X2 is about 0.5 . 10(3) s-1 at 300 degrees K (0.01 M phosphate buffer; 0.05% LDAO, pH 7.2). The activity of this transfer is exponentially reduced with a decrease in temperature within the range of 300 to 230 degrees K, with an activation energy, Ea, of approximately equal to 8 kcal. The recombination rate constant of light-induced ion-radicals, (BChl)2+ and X1-, was found to be 5 . 10(-2) s-1 at 180 degrees K. The preparations thus obtained can be used for studying mechanisms of primary events in photosynthesis and electron-exchange conformations in the reaction center.

Bacterial Proteins↗
PubMed1980

Electric field promotion of the bacteriorhodopsin BR570 to BR412 photoconversion in films of Halobacterium halobium purple membranes.

The combined action of electric field (105-107 V x m-1) and light (380-580 nm, 80 W x m-2) activating the photoenergetic reaction of bacteriorhodopsin (BR) in dry films of purple membranes from Halobacterium halobium was studied. A new stimulating effect of the field on the BR412 intermediate accumulation in the normal photochromic cycle of BR570 has been observed. The formation of the product BR412 is supposed to be accompanied by specific rearrangements of certain charged, polar and polarizable groups in the BR pigment-protein matrix. Such an intrinsic polarization could be promoted by an external electric field, the displacement vector of those groups being oriented in the direction of the filed. The dielectric polarization properties of the purple membranes have been demonstrated by electret-thermal analysis.

Bacteriorhodopsins↗
PubMed1980

Photo-induced electron transport and water state in Rhodospirillum rubrum chromatophores.

It is shown that in bacterial chromatophores the pronounced changes in the free water content with a proton spin-spin relaxation time (T2) of 10(-3)--10(-2) s does not influence the efficiency of electron transfer from the photosynthetic reaction centre to the membrane pool of secondary acceptors. An abrupt inhibition of this process occurs only after the loss of the water with faster proton spin-spin relaxation time (T2 of 10(-4) s). The process is reversible. The water fraction in question is obviously bound to the chromatophore proteins and forms the primary hydration layer.

Bacterial Chromatophores↗