Biomedical subjects
Publications and source records attributed to A B Rubin.
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Changes in the membrane-associated Ca2+ concentration and viscosity of the plasmatic membrane of P- and R-cells segmented ganglia of medicinal leech upon a variation of extracellular serotonin concentration were investigated. It is shown that the transmission of rhythmic excitation from P- to R-cells is due to the formation of the serotonin-dependent synapse and affects the distribution of the membrane-associated Ca2+ and intracellular processes controlling the viscosity of the membrane.
A comparative study was carried out of temperature dependence of kinetics of dark reduction of bacteriochlorophyll P870 oxidized both by pulsed laser and continuous actinic light in preparations of photosynthetic reaction centres-bacteriochlorophyll-protein complexes from Rhodopseudomonas spheroides, strain 1760-1. Half-time of the recombination of primary products--P870+ and reduced primary electron acceptor A1, which decreases with temperature lowering from 180-240 ms at 120K, is determined. Values of the rate constant of electron transfer from A1 to secondary acceptors at 29,K (2.7.10-1s-1) and the activation energy of this reaction in the range of 298-255K which is 11.8 kcal/mole are calculated.
The basic mechanisms of kinetic regulation of photosynthetic processes are considered, which provide a strict light regulation of electron transfer in photosynthetic reaction centers and a more flexible regulation at the level of interaction of photosystems, transmembrane ion fluxes and coupling with dark reactions of the Calvin cycle. A generalized model was developed, which integrates the modern knowledge about photosynthetic processes of higher plants. The general principles of multilevel regulation in photosynthetic systems are discussed.
The light-dependent reactivation of photosystem II in Chlorella pyrenoidosa Chick, CALU-175 cells, inactivated with supraoptimal temperatures (40-43 degrees C) in the dark or during heterotrophic growth was studied. It was shown that the inactivation of photosystem II after incubation in the dark at 41-42 degrees C, which showed up in the suppression of relative yield of variable chlorophyll fluorescence Fv due to an increase in yield F0 could be completely reversed by light. The inactivation of photosystem II at 43 degrees C in the dark could not be reversed by subsequent irradiation. In this case, the suppression of Fv/Fm was related not only to the growth of F0 but also with the decrease in Fm. The light dependences of the rate and extent of reactivation of yield Fv after heterotrophic growth or incubation of chlorella at 41 degrees C in the dark completely coincided. The full light-induced reactivation of photosystem II took place as the rate of photoinduced electron transport reached the rate of nonphotochemical reduction of plastoquinone in the dark. These results suggest that the light-reversed inactivation of photosystem II after heterotrophic growth or incubation at 41 degrees C in the dark is due to the redox-interaction of the primary quinone acceptor with plastoquinone reduced by the electron flux from the substrates of chlororespiration.
A model of electrodiffusion processes in the vicinity of cell membrane was developed. The model takes into account chemical reactions, Coulomb interactions between charged particles and the effect of external electric field. It was concluded that the applied electric field can change the characteristics of space-time patterns in the system. Dissipative structures slowly move and this is accompanied by a change in the number of structure elements. The characteristic equation includes odd powers of the wavenumber, which can lead to the appearance of soliton-like structures. The dissipative structures can appear not only due to the Turing diffusion instability but due to the disperse instability under electric field the applied.
A new concept illustrated by a corresponding mathematical model of nitrate metabolism regulation is proposed. The model is based on root nitrate compartmentation in several functional pools: storage, metabolic and a mobile pool which is intended for translocation to shoots. Data on nitrate uptake, compartmentation, reduction in intact roots and translocation to shoots were obtained on steady-state wheat seedlings grown at 25 and 12 degrees C in the root zone. The net uptake, influx/efflux ratio, mobile pool size and translocation changed depending on the medium temperature. The oscillations of the net uptake rate, nitrate tissue concentration were revealed and the effect of temperature on these changes was demonstrated. The scheme of regulation is based on the idea that net uptake through nitrate influx/efflux is under the control of the nitrate the mobile pool whose size was dependent on the nitrate translocation into shoots. The mathematical model is represented by a system of ordinary differential equations simplified according to the time hierarchy of reactions. It has a limit cycle at definite values of the parameters. The model postulates the mechanism of a positive feed-back regulation of the transfer of newly absorbed nitrate into translocated pool formed in the root cortex. Theoretical results are verified experimentally.
The role of membrane-bound Ca2+ in the regulation of Ca2+ transport through voltage-gated Ca2+ channel, and NMDA-glutamate and n-acetylcholine receptors upon interaction of a neuron with glia during rhythmic excitation was studied. It was found that the redistribution and transport of Ca2+ play a crucial role in the conductance of rhythmic excitation in both a "neuron-neuron" system and the processes providing the maintenance of a stationary level of rhythmic excitation in the system "neuron-glia".
Photosynthetic reaction centres were isolated from the cells of Rhodopseudomonas spheroides, strain 1760-1, using sodium dodecyl sulphate. The preparations purified by precipitation with ammonium sulphate showed absorbance ratios of A280 : A800=2.1. and A765 : A800 : A870=1 : 2 : 1; about 75% of the bacteriochlorophyll absorbing at 870 nm (P870) were photochemically active. Both absolute and difference "light minus dark" absorption spectra were obtained for the reaction centre suspensions and vacuum-dried films at room and low temperatures. Shift to the longer wavelength of the 870 nm absorption band resulting from temperature lowering suggests the existence of temperature-determined conformations of the bacteriochlorophyll-protein complex of the reaction centres. Characteristic time of an electron transfer from the photoexcited P870 to the primary intermediate of photochemical process as evaluated from the data of pulsed laser fluorometry of the reaction centres was found to be (21--15)+/-8 picoseconds. The oxidized P870 dark reduction kinetics dependence on the actinic light intensity gives evidence for the functioning of heterogeneous pool of the secondary electron acceptors in the reaction centre preparations. Filling in of this pool with electrons is decreased under temperature lowering or vacuum drying and its electron capacity is limited under isooctane treatment resulting in ubiquinon extraction. The ability of the reaction centre preparations to catalyze the photochemical oxidation of iminoxyl aromatic radical was demonstrated.
In isolated photosynthetic reaction centres of Rps. spheroides and chromatophores R. rubrum the spectral position of the longest wavelength absorption band of P870, effectiveness of electron removal from the photochemical pair (P870 -- primary electron acceptor, A1) and the rate constant for recombination of photooxidized P870 with photoreduced A1 undergo marked and fully reversible changes over the temperature interval from +20 to -70 degrees. Dehydration of the samples has the effect similar to that induced by temperature lowering. The data suggest that the spectral position of the main maximum of pigment complex P870 absorption band may be regarded as a sensitive inner probe of the structure-functional state of the investigated preparations.
The temperature dependencies of the photoconversion of pigments P870--P890 were studied using isolated chromatophores and photosynthetic reaction centres (RC's) of purple bacteria. The samples were prepared by extraction with organic solvents (light petroleum and a combination of light petroleum and methanol) and modified through cross-linking the functional groups of proteins by treatment with glutaraldehyde or denatured by various physical and chemical treatments. The data provide further evidence that the pool of RC secondary acceptors is formed by the compounds of quinone nature located in the hydrophobic surrounding. Similar molecules localized in a more polar medium act as primary acceptors. The findings indicate on the essential role of macromolecular components in the RC's functioning and also suggest that the photochemical charge separation is conformation-controlled.