Adsorption of ruthenium red to phospholipid membranes

We have measured the distribution of the hexavalent ruthenium red cation (RuR) between water and phospholipid membranes, have shown the critical importance of membrane negative surface charge for RuR binding, and determined the association constant of RuR for different phospholipid bilayers. The stu...

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Bibliographic Details
Published in:Biophysical journal 1996-02, Vol.70 (2), p.818-830
Main Authors: Voelker, D., Smejtek, P.
Format: Article
Language:English
Subjects:
Adsorption
Biophysical Phenomena
Biophysics
Electrochemistry
In Vitro Techniques
Lipid Bilayers - chemistry
Liposomes - chemistry
Membrane Potentials
Models, Chemical
Ruthenium Red - chemistry
Ruthenium Red - pharmacokinetics
Sarcoplasmic Reticulum - chemistry
Sarcoplasmic Reticulum - metabolism
Surface Properties
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Summary:We have measured the distribution of the hexavalent ruthenium red cation (RuR) between water and phospholipid membranes, have shown the critical importance of membrane negative surface charge for RuR binding, and determined the association constant of RuR for different phospholipid bilayers. The studies were performed with liposomes made of mixtures of zwitterionic L-alpha-phosphatidylcholine (PC), and one of the negatively charged phospholipids: L-alpha-phosphatidylserine (PS), L-alpha-phosphatidylinositol (PI), or L-alpha-phosphatidylglycerol (PG). Lipid composition of PC:PX membranes was 1:0, 19:1, 9:1, and 4:1. Liposomes were processed using freeze-and-thaw treatment, and their size distribution was characterized by light scattering and electron microscopy. Experimental distribution isotherms of RuR obtained by ultracentrifugation and spectrophotometry can be reproduced with the Langmuir-Stern-Grahame model, assuming that RuR behaves in the diffuse double layer as an ion with effective valency < 6. In terms of this model, PC-PS, PC-PI, and PC-PG membranes were found to be electrostatically equivalent and the intrinsic association constants of RuR were obtained. RuR has highest affinity to PS-containing membranes; its association constant for PC-PI and PC-PG membranes is about 5 times smaller than that for PC-PS membranes. From the comparison of RuR binding to mixed negatively charged phospholipid membranes and RuR binding to sarcoplasmic reticulum (SR), we conclude that the low-affinity RuR binding sites may indeed be associated with the lipid bilayer of SR.
ISSN:0006-3495
1542-0086
DOI:10.1016/S0006-3495(96)79621-2