Reconstitution of membranes with fractions of triton X-100 which are easily removed.

Triton X-100 is a neutral detergent which is often employed for reconstitution of lipidprotein membranes. It is, however, difficult to remove entirely from the final reconstituted membrane preparation. We have analyzed the molecular components of the Triton X-100 complex of molecules that remain in reconstituted membranes which are prepared by, first, Triton X-100 solubilization and, second, by detergent removal with polystyrene beads and gel filtration. The analysis was performed with radioactive Triton X-100 and by silica gel chromatography. It showed that the components of Triton X-100 that are difficult to remove from a membrane are the highand low-molecular-weight ones. Using only an intermediate-molecular-weight, radioactive Triton, lipids and Sindbis virus envelope proteins have been solubilized and used to prepare reconstituted membranes which retain half as many Triton/lipid molecules, or one-fifth as many Triton/protein molecules as do vesicles prepared with complete Triton X-100. The membranes prepared with fractionated Triton are also of more homogeneous size, by gel chromatography, than are membranes prepared with unfractionated Triton.