Lysolecithin-cholesterol interaction. A spin-resonance and electron-micrographic study

Another publication (rand, R. P., Pangborn, W., Purdon, A. D., and Tinker, D. O.(1975) Can. j. Biochem. 53, 189-195) has established that lysolecithin and cholesterol interact to form an equimolar complex. We have investigated this complex using the techniques of electron spin resonance (e.s.r) and electronmicroscopy. By varying the cholesterol concentration with lysolecithin in both thin films and dispersions studied by these techniques, we have observed the interaction between lysolecithin and equimolar complex below 50 mol % cholesterol, and between crystalline cholesterol and equimolar complex above 50 mol % cholesterol. We have observed an interesting alteration in morphology by electron microscopy, and an isotropic to anisotropic spectral change using 3-dosylcholestane and 12-doxylstearic acid spin-labelled probes when the cholesterol concentration is increased from 20 to 33 mol %. The equimolar complex is stable in the presence of crystalline cholesterol, and exhibits no phase changes in the physiological temperature range. Implications for membrane structure are discussed.