Carotenoids in DPPC vesicles: membrane dynamics

Incorporation of carotenoids into membranes is supposed to change their physical properties with consequences to signal transduction and membrane protein activities. Here the physical parameters membrane fluidity, micropolarity and anisotropy are considered and measured in multilamellar and unilamellar vesicles of dipalmitoylphosphatidyicholine (DPPC) after incorporation of 1, 2.5 and 5 mol% beta-carotene, lutein, zeaxanthin, canthaxanthin, or astaxhanthin 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 change 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 significantly only by those carotenoids which incorporate worst into the membrane. This leads to the hypothesis that carotenoid incorporation into membranes is governed not only by carotenoid polarity hut also by their ability to change membrane anisotropy. (C) 1999 Elsevier Science B.V. All rights reserved.