Carotenoids in DPPC vesicles: membrane dynamics

Incorporation of carotenoids into membranes is supposed to change their phy sical properties with consequences to signal transduction and membrane prot ein activities. Here the physical parameters membrane fluidity, micropolari ty and anisotropy are considered and measured in multilamellar and unilamel lar vesicles of dipalmitoylphosphatidyicholine (DPPC) after incorporation o f 1, 2.5 and 5 mol% beta-carotene, lutein, zeaxanthin, canthaxanthin, or as taxhanthin using 4 mol% pyrene or 1 mu M 1,6-diphenyl-1,3,5-hexatriene (DPH ) as fluorescent labels. Contrary to other investigations, no significant c hange in membrane fluidity (as evaluated by the pyrene excimer method) can be found. But a change of micropolarity in the pyrene label environment is obtained from the pyrene monomer fluorescence emission fine structure after incorporation of carotenoids. The membrane anisotropy is enhanced signific antly only by those carotenoids which incorporate worst into the membrane. This leads to the hypothesis that carotenoid incorporation into membranes i s governed not only by carotenoid polarity hut also by their ability to cha nge membrane anisotropy. (C) 1999 Elsevier Science B.V. All rights reserved .