Competitive incorporation of carotenoids and cholesterol into microsomal membranes

Liposomes were used as carriers to incorporate carotenoids (beta-carotene, lutein and zeaxanthin) and/or cholesterol into pig liver microsomes. The incorporation yields were calculated from the UV-Vis spectra of the carotenold- and/or cholesterol-doped liposomes. Although mostly the incorporation of carotenoids and cholesterol into microsomal membranes is competitive, lutein favours the incorporation of cholesterol. Vice versa, cholesterol determines the lutein location in the membrane: lutein molecules dislocate from a partly membrane plane parallel to a more membrane perpendicular position. The fluorescent dyes Laurdan and Dil-C-18 that locate in different regions of the bilayer were used to label the doped microsomes. Both dyes get quenched. The different way of their quenching indicates a different way of their interaction with the carotenoids. Laurdan interacts directly with them but Dil-C-18 is displaced.