Probing the lateral organization of membranes: fluorescence repercussions of pyrene probe distribution

Phospholipids pyrene labeled are widely used to investigate dynamics and or ganizations of membranes. We studied pyrene probe lateral distribution by a nalyzing the variations of the molar absorption coefficient (epsilon) versu s probe concentrations,, in small unilamellar vesicles (SUV) made of phosph olipids and/or glycolipids, with pyrene labeled phosphatidylcholine (PyPC) or phosphatidylglycerol (PyPG). The results were interpreted according to a n infinite associative model. They indicated that an effective self-associa tion process corresponding to K ranging from 30 to 100 M-1 occurred with th ose probes incorporated in dimannosyl diacylglycerol (DMDG). In contrast, a fter SUV labeling of egg yolk phosphatidylcholine (EggPC) or phosphatidylgl ycerol (EggPG), K values < 1 M-1 were determined. The corresponding percent ages of various stacked forms of pyrene probes were calculated. They indica ted that, for a 3% PyPG labeling, the monomer represented 21% of n-mers in DMDG and 94% in EggPC. The analysis of fluorescence experiments carried out on the same samples indicated that: (i) the fluorescence process of pyrene probes was generated by the monomers; and (ii) the excimer forming resulte d from a diffusional encounter between one excited and one non-excited mono mer. A correction of fluorescence data allowing a more correct interpretati on of fluorescence measurements was proposed. (C) 2001 Elsevier Science BN. All rights reserved.