| Regional Biophysics Meeting 2005, March 16-20, Zreče, Slovenia | [MembBiophys] |
Model membranes composed of different lipid constituents exhibit coexistence of diverse lipid phases for appropriate temperature or composition. Since lipids in different phases display different structural and motional properties it is expected that the corresponding spin probe electron paramagnetic resonance (EPR) spectra will be superimpositions of several spectral components. From comparison of proportions of spectral components of EPR spectrum with the fractions of corresponding lipid phases obtained from known phase diagrams the partition coefficient of spin probe between different lipid phases can be established. The aim of our study was to determine the partition coefficient of spin probe MeFASL(10,3) (methyl ester of 5-doxyl palmitate) between coexisting lipid phases in two binary mixtures: dimyristoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DMPC/DPPC) and dimyristoylphosphatidylcholine/cholesterol (DMPC/Chol). The first mixture exhibits liquid-disordered/gel (Ld/S) phase coexistence, while in the second one gel/liquid-ordered (S/Lo) and liquid-disordered/liquid-ordered (Ld/Lo) phase coexistence are possible. The EPR spectra of model membranes were decomposed into two spectral components, because the phase diagrams for the used mixtures show that two lipid phases coexist at the most. The measured temperature dependence of the proportions of spectral components of EPR spectra was compared to the calculated temperature dependence of fractions of corresponding lipid phases. It can be concluded from this comparison that MeFASL(10,3) partitions approximately equally between different phases. The knowledge of partitioning of the spin probe between lipid regions of different properties permits accurate estimation of proportions of different lipid domain types in biological membranes.
Email: zoran.arsov@ijs.si
Address: Laboratory of Biophysics,