Cholesterol Perturbs Lipid Bilayers Nonuniversally

Cholesterol is well known to modulate the physical properties of biomembranes. Using modern x-ray scattering methods, we have studied the effects of cholesterol on the bending modulus K_C, the thickness D_HH, and the orientational order parameter S_xray of lipid bilayers. We find that the effects are different for at least three classes of phospholipids characterized by different numbers of saturated hydrocarbon chains. Most strikingly, cholesterol strongly increases K_C when both chains of the phospholipid are fully saturated but not at all when there are two monounsaturated chains.