Hydrophobic interaction of alkanes with liposomes and lipoproteins.

Human serum lipoproteins and egg yolk lecithin liposomes are able to solubilize large amounts of n-hexane and n-octane. At the maximum water solubility of n-octane the mole ratio of alkane to lipoprotein was 65 for high density lipoprotein (holo-HDL) and 900 for low density lipoprotein (holo-LDL). Alkane binding to lipid-free apo-HDL is negligible compared to alkane solubility in holo-HDL. Alkane solubility in the lipoproteins and liposomes is thermodynamically consistent with the simple soution of hydrocarbon in the hydrophobic regions of these particles. The unitary free energies of alkane transfer are similar to values previously observed for detergent micelles but are less favorable by 0.8 kcal/mol from the free energy of transfer to liquid hydrocarbon. It is concluded that the thermodynamics of alkane transfer to the lipoproteins resembles that found for detergent micelles or liposomes rather than that anticipated for an "oil drop" (i.e. liquid hydrocarbon).