Abstract

A series of lipid probes, phosphatidylcholines labeled with Me4-BODIPY-8 (4,4-difluoro-1,3,5,7- tetramethyl-4-bora-3a,4a-diaza-s-indacen-8-yl) fluorophore attached to the end of an acyl residue at different distances from the polar head, were used as depth-dependent probes for the apolar zone of model membrane systems, large unilamellar vesicles (LUVs). Data on the anisotropy of probe fluorescence demonstrated different mobility profiles for the fluorophore microenvironment in LUVs of different composition at various temperatures, which indicates a high sensitivity of these probes as tools for studying membrane systems. An interesting anomaly was observed for LUVs from dimiristoylphosphatidylcholine (DMPC) or from a DMPC-cholesterol mixture: the anisotropy of the fluorophore located near the bilayer center is larger than that of the fluorophore located further from the center; i.e., the mobility of the microenvironment is lower in the first case. This anomaly is supposed to result from the penetration of the unlabeled long chain of the probes into the opposite bilayer leaflet. Such a possibility should be taken into account in constructing fluorescent probes and interpreting the results.