Insolubility of lipids in Triton X-100: physical origin and relationship to sphingolipid/cholesterol membrane domains (rafts)

The insolubility of lipids in detergents is a useful method for probing the structure of biological membranes. Insolubility in detergents like Triton X-100 is observed in lipid bilayers that exist in physical states in which lipid packing is tight. The Triton X-100-insoluble lipid fraction obtained after detergent extraction of eukaryotic cells is composed of detergent-ins oluble membranes rich in sphingolipids and cholesterol. These insoluble mem branes appear to arise from sphingolipid- and cholesterol-rich membrane dom ains (rafts) in the tightly packed liquid ordered state. Because the degree of lipid insolubility depends on the stability of lipid-lipid interactions relative to lipid-detergent interactions, the quantitative relationship be tween rafts and detergent-insoluble membranes is complex, and can depend on lipid composition, detergent and temperature. Nevertheless, when used cons ervatively detergent insolubility is an invaluable tool for studying cellul ar rafts and characterizing their composition. (C) 2000 Elsevier Science B. V. All rights reserved.