ABSTRACT
Using microelectrophoresis and electric light scattering techniques, we investigated the adsorption characteristics, surface coverage and surface electric parameters of superstructures from two isoforms of plastocyanin, PCa and PCb, in an oxidized state adsorbed on beta-ferric hydrous oxide particles. The surface electric charge and electric dipole moments of the composite particles and the thickness of the protein adsorption layer are determined in a wide pH range, at different ionic strengths and concentration ratios of PC to beta-FeOOH. The adsorption of the two proteins was found to shift the particles' isoelectric point and to alter the total electric charge and the electric dipole moments of the oxide particles to different extent. A "reversal" in the direction of the permanent dipole moment is observed at lower pH for PCb- than for PCa-coated oxide particles. Strict correlation is found between the changes in the electrokinetic charge of the composite particles and the variation in their "permanent" dipole moments. Data suggest that the adsorption of the proteins is driven by electrostatic and/or hydrophobic interactions with the oxide surfaces dependent on pH. The adsorption behaviour is consistent with the involvement of the "eastern" and "northern" patches of the plastocyanin molecules in their adsorption on the oxide surfaces that are differently charged depending on pH.
Subject(s)
Electrochemistry/methods , Ferric Compounds/chemistry , Plastocyanin/chemistry , Plastocyanin/pharmacokinetics , Proteins/chemistry , Adsorption , Coated Materials, Biocompatible , Electrophoresis/methods , Hydrogen-Ion Concentration , Isoelectric Point , Isomerism , Light , Models, Chemical , Osmolar Concentration , Particle Size , Protein Conformation , Protein Isoforms/chemistry , Rotation , Scattering, Radiation , Surface PropertiesABSTRACT
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.
Subject(s)
Chlorophyll/physiology , Hordeum/physiology , Photosynthetic Reaction Center Complex Proteins/metabolism , Thylakoids/physiology , Chlorophyll/genetics , Electricity , Hordeum/genetics , Hordeum/radiation effects , Kinetics , Light , Light-Harvesting Protein Complexes , Protein Kinases/metabolism , Scattering, Radiation , Thylakoids/ultrastructureABSTRACT
Temperature-induced changes in protein intrinsic fluorescence of native, delipidated and deionized purple membranes are investigated. It is found that the removal of cations most strongly affects the protein and its thermal stability. The denaturation of dei-BR completes at 70 degrees C, while delipidated and native BR still maintain their native structure at this temperature. Both the quantum yield and the fluorescence maximum suggest correlation between the Trp-retinal coupling and protein structural stability. The low red shift of the fluorescence maximum caused by increasing of temperature indicates limited unfolding of bacteriorhodopsin upon denaturation.
Subject(s)
Bacteriorhodopsins/chemistry , Cations , Drug Stability , Halobacterium salinarum/metabolism , Hot Temperature , Lipids/chemistry , Protein Denaturation , Spectrometry, Fluorescence , ThermodynamicsABSTRACT
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 II(1)) to monomeric (LHC II(3)) 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.
ABSTRACT
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.
