Ivana Petkanchin

Electric properties of thylakoid membranes from pea mutants with modified carotenoid and chlorophyll-protein complex composition

Surface electric properties of thylakoid membranes from wild type and two mutant forms, Coeruleovireus 2/16 and Costata 2/133, of pea are investigated by electric light scattering and microelectrophoretic measurements. Characterization of the chlorophyll–protein complexes in thylakoid membranes reveals that the relative ratio of oligomeric (LHC II1) to monomeric (LHC II3) forms of the light-harvesting Chl a/b complex of Photosystem II is lower (3.34) in 2/133 mutant and higher (6.62) in 2/16 mutant than in wild type (4.57). This is accompanied by elevated amounts and a considerable reduction of all carotenoids in 2/16 and 2/133 mutant, respectively, as compared to the wild type. The concomitant variations of the permanent dipole moment (transversal charge asymmetry), electric polarizability and electrokinetic charge of the thylakoid membranes from both the mutants are discussed in terms of the differences in the supramolecular (oligomeric) organization of the light-harvesting complexes II within the photosynthetic apparatus.

Effect of pectin charge density on formation of multilayer films with chitosan.

The effect of pectin charge density on the formation of multilayer films with chitosan (PEC/CHI) is studied by means of electro-optics. Pectins of low (21%) and high (71%) degrees of esterification, which are inversely proportional to the pectin charge density, are used to form films on colloidal beta-FeOOH particles at pH 4.0 when the CHI is fully ionized. We find that, after deposition of the first 3-4 layers, the film thickness increases linearly with the number of adsorbed layers. However, the increase in the film thickness is larger when the film is terminated with CHI. Irregular increase of the film thickness is more marked for the PEC with higher density of charge. Oscillation in the electrical polarizability of the film-coated particles with the number of deposited layers is also registered in the PEC/CHI films. The charge balance of the multilayers, calculated from electrical polarizability of the film-coated particles, is positive, with larger excess of positive charge within the film constructed from CHI and less charged PEC. This is attributed to the ability of CHI to diffuse into the film at each deposition step. Despite the CHI diffusion, the film thickness increases linearly due to the dissolution of unstable PEC/CHI complexes from the film surface.

Comparison of electric light scattering and birefringence for polydisperse suspensions

SummaryA review is made of the existing theoretical expressions, describing the change of the scattered light intensity and the birefringence by application of an electrical field to a colloid solution.Furthermore, the geometrical functions for disc-shaped particles are calculated in this article for the case of electric light scattering and are. presented graphically. In addition, expressions are derived for the average value of the electrical polarizability (γ) for the case of polydisperse solutions.ZusammenfassungEs wird ein überblick über die existierenden theoretischen Beziehungen gegeben, die die Änderung der Intensität des Streulichtes und der Doppelbrechung von Kolloidsuspensionen im elektrischen Feld beschreiben.Weiterhin sind die geometrischen Funktionen für scheibchenförmige Teilchen in dieser Arbeit für den Fall der elektrooptischen Lichtstreuung berechnet und grafisch dargestellt. Außerdem werden Beziehungen für den Mittelwert der elektrischen Polarisierbarkeit (γ) für den Fall polydisperser Suspensionen abgeleitet.

INTERACTION OF HUMIC SUBSTANCES WITH SILICA AND ALUMINA COLLOIDS: ADSORPTION AND STABILITY. ELECTRO-OPTICAL STUDY

Abstract The adsorption of a humic substance — Na-humate — on aluminium oxide (γ-Al 2 O 3 ) and aerosil (SiO 2 ) particles was investigated using electric light scattering and electrophoresis. The electro-optic effect in γ-Al 2 O 3 dispersion is changed when varying the concentration of the humate polyanion and reduces to zero together with the electrophoretic mobility. A decrease of the rotation diffusion coefficient was registered above the isoelectric point (IEP), which indicates formation of a thick adsorption layer, stabilizing the dispersed system. The electro-optic effect relaxation frequency of the stabilized dispersed particles is greatly decreased, which is evidence of decreased counterion mobility. In the aerosil dispersed system the electro-optic effect increases with the addition of Na-humate. The frequency dependence of the electro-optic effect is also influenced by the presence of negative polyions. These changes in the electro-optic behaviour of the aerosil suspension are an indication of the fact that the polyion is adsorbed on a negatively charged surface, probably because of a strong specific interaction.

SURFACE ELECTRIC PROPERTIES OF THYLAKOID MEMBRANES FROM ARABIDOPSIS THALIANA MUTANTS

Electric light scattering measurements of thylakoid membranes from wild type and two mutant forms (JB67 and LK3) of Arabidopsis thaliana have shown that application of external electric pulses induces electric dipole moments of different origin. The asymmetric surface charge distribution and electric polarizability are significantly altered by the lipid modification. Mild trypsin treatment of Arabidopsis thylakoids leading to digestion of small polypeptides from the light-harvesting chlorophyll a/b protein complex of photosystem II (LHCP II) gives evidence for a lower content of LHCP II in the mutant forms. The results demonstrate the significance of the level of thylakoid lipid unsaturation in determining the surface charge distribution through changes either in the pigment-protein content and membrane appression induced by the lipid modification or in the exposure of charged polypeptides on the thylakoid membrane surface(s) arising from alteration of the lipid geometry.

Electro-optics of colloids coated with multilayers from strong polyelectrolytes:surface charge relaxation.

The electrical properties and structure of polyelectrolyte multilayers prepared by layer-by-layer deposition of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) on ellipsoidal beta-ferric hydrous oxide particles are examined in situ using the electric light scattering method. In the initial nonlinear growth regime, the electro-optical effect is found to increase almost in the same manner as the thickness of the multilayer film. This reveals an increase in the multilayer surface charge due to the nonlinear increase in polyelectrolyte adsorption. Above five deposition cycles, the electro-optical effect reaches a plateau and the thickness increment per layer becomes constant, indicating regular film growth. Evidence is given that the concentration of small residual ions incorporated into the PSS/PDADMAC film is negligible. Polarization of counterions, bound near to the surface of the last-adsorbed polyion, is assumed to explain the relaxation of the electro-optical effect in the frequency range 10(3)-10(5) Hz.

Structure of polyelectrolyte layers on colloidal particles at different ionic strengths

Abstract The structure of polystyrenesulfonate (PSS) layer adsorbed onto ellipsoidal β-ferric hydrous oxide (β-FeOOH) particles is examined using electro-optics. Changes in the thickness are investigated by varying the ionic strength of the solution for rinsing the adsorbed PSS layer. An increase in the layer thickness is found after rinsing with water, which turns to a decrease when salt (NaCl) is added to the rinsing solution. No changes are registered if formation and rinsing of the layer is carried out at constant ionic strength. Compression of the PSS layer is also found after adsorption of an oppositely charged polyethylenimine (PEI) on the layer rinsed with water or in the presence of 10 −4 M NaCl. Complex-formation between the two oppositely charged polyions on the particle surface is supposed to explain the behavior of the polyelectrolyte bilayer.

Electrooptic study of the deionized form of bacteriorhodopsin

Electric field induced light scattering by suspensions of cation-depleted purple membranes, obtained by deionization of purple membrane (PM) suspensions on a cation exchange column or by electrodialysis at a pH around 6, shows a strong drop (more than 5 times) in the value of the permanent dipole moment relative to that of PM fragments. The membrane dipole moments were measured both at low dc and ac electric fields as well as by using electric field pulses with reversing polarity. Some slight changes in the dispersion of the electric polarizability were also observed.Microelectrophoretic measurements showed that the electric charge of the membrane fragments is increased by 30% after deionization. The importance of these data for the understanding of the blue membrane properties and subsequently for the mechanism of proton pumping are discussed.

Interaction of biological membranes with substituted 1,4-anthraquinones

Abstract The interaction of the substituted 1,4-anthraquinones with purple membranes (PM) is studied by the fluorescence and electric light scattering techniques. Substituted 1,4-anthraquinones are shown to quench bacteriorhodopsin tryptophan fluorescence. The quenching efficiency of 1,4-anthraquinone derivatives is smaller than that of 1,4-anthraquinone. It is the smallest at di-substituted 1,4-anthraquinones (R9=OCOCH 3 and R3=Cl or Br). The type of the halogen atom as substituent does not affect the quenching efficiency of di-substituted 1,4-anthraquinones (R9=OH or OCOCH 3 and R3=Cl or Br). The quenching efficiency depends on the position of the Cl atom for di-substituted 1,4-anthraquinone derivatives (R9=OH and R3=Cl or R9=OH and R10=Cl). 9-Hydroxy-1,4-anthraquinones induce decrease in purple membrane charge asymmetry distribution whereas mono-substituted 1,4-anthraquinones containing R9=OCH 3 or R9=OCOCH 3 induce increase in the membrane charge asymmetry. The membrane electric polarizability, related to the structure and dynamics of the electric double layer, decreases in the presence of 1,4-anthraquinone derivatives, the greatest effect being observed for the 9-hydroxy-1,4-anthraquinones. The energy transfer and the quenching of bR tryptophan fluorescence from 9-hydroxy-1,4-anthraquinones correlate with the variation of the surface electric properties of PM in the presence of relatively low concentrations of substituted 1,4-anthraquinones.

Contribution of LHC II complex to the electric properties of thylakoid membranes: an electric light scattering study of Chl b-less barley mutant.

Electric light scattering measurements demonstrate a strong decline in the permanent electric dipole moment and electric polarizability of both thylakoid membranes and photosystem II-enriched particles of the Chlorina f2 mutant which has severely reduced levels of light-harvesting chlorophyll a/b-binding proteins compared to the wild type barley chloroplasts. The shift in the electric polarizability relaxation to higher frequencies in thylakoids and photosystem II particles from Chlorina f2 reflects higher mobility of the interfacial charges of the mutant than that of the wild type membranes. The experimental data strongly suggest that the major light-harvesting complex of photosystem II directly contribute to the electric properties of thylakoid membranes.