Sphingomyelin-lecithin bilayers and their interaction with cholesterol

Abstract

Utilizing X-ray diffraction and differential scanning calorimetry (DSC), the structure and thermotropic properties of hydrated N-palmitoylsphingomyelin, the interaction of N-palmitoylsphingomyelin with dimyristolyllecithin and the interaction of cholesterol with N-palmitoylsphingomyelin and dimyristoyllecithin, both individually and in a 50:50 (mol/mol) mixture, were studied. N-Palmitoylsphingomyelin forms bilayers which undergo a thermotropic order-disorder (gel-liquid crystalline) transition at 40.5.degree. C (.DELTA.H = 5.8 kcal/mol). The bilayer repeat distance is 66.8 .ANG. at 10.degree. C and 61.6 .ANG. at 50.degree. C. N-Palmitoylsphingomyelin exhibits miscibility with dimyristoyllecithin in both the gel and liquid-crystalline phases, and no lateral phase separation occurs. Scanning calorimetry indicates that interaction with cholesterol is similar for both N-palmitoylsphingomyelin and dimyristoyllecithin and that in a 50:50 (mol/mol) mixture cholesterol shows no preferential affinity for either phospholipid.