(B) Representative emission spectra of mixtures containing ECFP-D4H, mVenus-Lact-C2, and liposomes containing indicated compositions of lipids. Note that FRET signal was increased in the presence of both cholesterol (50%) and phosphatidylserine (DOPS) (20%) and that FRET signal was decreased when sphingomyelin (SM) (25%) was additionally incorporated into the liposomes. Asterisks indicate positions of emission maximum of ECFP (*477 nm) and FRET (**525 nm). DOPC, phosphatidylcholine (1,2-dioleoyl-sn-glycero-3-phosphocholine); DOPS, phosphatidylserine (1,2-dioleoyl-sn-glycero-3-phospho-L-serine); Chol., cholesterol; SM, sphingomyelin (N-oleoyl-D-erythro-sphingosylphosphorylcholine). (C) Quantification of the ratio of FRET signal at 525 nm to ECFP emission at 480 nm (FRET/ECFP) (see Materials and Methods) from mixtures as shown in (D) (mean ± SEM, n = 4 independent experiments; Dunnett's multiple comparisons test, **P < 0.0001). 