Analysis of the domain structure of membranes by fragmentation and separation in aqueous polymer two-phase systems

Partitioning and concentrating biomaterials in aqueous phase systems

Aqueous phase separation is a general phenomenon which occurs when structurally distinct water-soluble macromolecules are dissolved, above certain concentrations, in water. The number of aqueous phases obtained depends on the number of such distinct macromolecular species used. Aqueous two-phase systems, primarily those containing poly(ethylene glycol) and dextran, have been widely used for the separation of biomaterials (macromolecules, membranes, organelles, cells) by partitioning. The polymer and salt compositions and concentrations chosen greatly affect the physical properties of the phases. These, in turn, interact with the physical properties of biomaterials included in the phases and affect their partitioning. Specific extractions of biomaterials can be effected by including affinity ligands in the systems. The phase systems can also be used to obtain information on the surface properties of materials partitioned in them; to study interactions between biomaterials; and to concentrate such materials.

Characterization of a non-detergent PS II-cytochrome b/f preparation (BS)

A non-detergent photosystem II preparation, named BS, has been characterized by countercurrent distribution, light saturation curves, absorption spectra and fluorescence at room and at low temperature (-196°C). The BS fraction is prepared by a sonication-phase partitioning procedure (Svensson P and Albertsson P-Å, Photosynth Res 20: 249-259, 1989) which removes the stroma lamellae and the margins from the grana and leaves the appressed partition region intact in the form of vesicles. These are closed structures of inside-out conformation. They have a chlorophyll a/b ratio of 1.8-2.0, have a high oxygen evolving capacity (295 μmol O2 per mg chl h), are depleted in P700 and enriched in the cytochrome b/f complex. They have about 2 Photosystem II reaction centers per 1 cytochrome b/f complex.The plastoquinone pool available for PS II in the BS vesicles is 6-7 quinones per reaction center, about the same as for the whole thylakoid. It is concluded, therefore, that the plastoquinone of the stroma lamellae is not available to the PS II in the grana and that plastoquinone does not act as a long range electron transport shuttler between the grana and stroma lamellae.Compared with Photosystem II particles prepared by detergent (Triton X-100) treatment, the BS vesicles retain more cytochrome b/f complex and are more homogenous in their surface properties, as revealed by countercurrent distribution, and they have a more efficient energy transfer from the antenna pigments to the reaction center.

Heterogeneity of smooth endoplasmic reticulum from rat liver studied by two-phase partitioning

Smooth microsomal membranes, prepared from rat liver by sucrose-density-gradient centrifugation, were subfractionated by counter-current distribution in an aqueous two-phase system consisting of poly(ethylene glycol) and Dextran T500. A comparison of the distribution curves of marker enzymes, together with theoretically calculated curves, indicated the presence of at least five membrane subfractions, differing in the ratios of the marker enzymes. Glucose-6-phosphatase and arylesterase distributed in one manner, and NADPH-cytochrome c reductase and NADH-ferricyanide reductase in another. Evidence for further heterogeneities in the distribution of marker enzymes in smooth microsomes was obtained by analysing the membrane domain structure using a recently described method [Albertsson (1988) Q. Rev. Biophys. 21, 61-98]. Phenobarbital treatment did not influence the behaviour of the marker enzymes.