We have studied the electrostatic and other interactions of the inorganic, hexavalent dye Ruthenium Red (RR) with phospholipid vesicles composed of phosphatidylcholine (PC) and phosphatidylserine (PS) or phosphatidylinositol (Pl) in various mixtures and concentrations. Experiments were based on spectrophotometric absorption measurements which compared RR concentrations in the presence and in the absence of liposomes at different dye concentrations. Multilamellar liposomes were obtained by handshaken preparations. Five freeze-and-thaw cycles of the lipid-RR suspension produced an ion equilibrium distribution at the membrane-water interface. Results are given in terms of the Gouy-Chapman-Stem adsorption theory with the linear partition coefficient and a newly introduced effective ion valency as parameters. Data on the time stability of RR solutions and their interaction with laboratory equipment are given. Furthermore, we characterize the freeze-and-thawing process and present an electron micrograph of liposomes. Two main results were found. First, the Gouy-Chapman-Stem theory correctly describes adsorption of a hexavalent ion to charged phospholipid vesicles if an effective valency is introduced. The effective valency accounts for the finite size of the ions and the repulsion between the ions. Values ranged between 2.9 and 4.1. Effective valencies decrease with increasing membrane surface charge density and are independent of the lipid concentration. Second, Ruthenium Red adsorbs to phospholipids and the adsorption is strongly related to the surface charge density of the membrane. Vesicles made from a mixture of PC and PI adsorb significantly less than vesicles made from a mixture of PC and PS. The second result is of special interest for molecular biology since biological membranes consist to a large extent of phospholipids. Sarcoplasmic reticulum (SR) membranes are discussed as an example. Liposomes (PC:PS 20: 1) with surface charge densities comparable to SR membranes adsorb a maximum of about 9±3nmol RR per mg lipid.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5953 |
| Date | 06 July 1994 |
| Creators | Voelker, Dirk |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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