Depth-Dependent Investigation of the Apolar Zone of Lipid Membranes Using a Series of Fluorescent Probes, Me4-BODIPY-8-Labeled Phosphatidylcholines

A. V. Omel’kov1, Yu. B. Pavlova1, I. A. Boldyrev1 and Jul. G. Molotkovsky1 #

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1 Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, Moscow, 117997, Russia

Received: December 18, 2006;  in final form: January 15, 2007

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 acyl residue at different distances from the polar head, were used as depth-dependent probes for the apolar zone of the model membrane systems, large unilamellar vesicles (LUV). Data on the anisotropy of probe fluorescence demonstrated a 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 unlabeled long chain of the probes to the opposite bilayer leaflet. Such a possibility should be taken into account when constructing the fluorescent probes and interpreting the results.

Key words:  bilayer structure; BODIPY; fluorescence anisotropy; fluorescent lipid probes

Russian Journal of Bioorganic Chemistry 2007, 33(5): 505-510