Synthesis and fluorescence properties of novel transmembrane probes and determination of their orientation within vesicles

Two novel transmembrane fluorescent diester probes D and E bearing an anthr acenediyl moiety in the middle of the molecule have been synthesized. Their absorption and fluorescence spectra in CHCl3 solution as well as their flu orescence characteristics in dimyristoylphosphatidylcholine (DMPC) large un ilamellar vesicles were determined. Although their absorption spectra (firs t transition, S-0 --> S-1) present a good overlap with the fluorescence spe ctrum of tryptophan, only probe E could be a good acceptor for the energy-t ransfer experiments, since a strong overlap exists between the absorption s pectrum of tryptophan and the second transition (S-0 --> S-2) of the absorp tion spectrum of probe D. The Forster critical distance R-0 for energy tran sfer between tryptophan (donor) and probe E (acceptor) is found to be 23-24 Angstrom. Finally, linear-dichroism studies on shear-deformed DMPC vesicle s show the incorporated probe E to lie essentially perpendicular to the bil ayer plane. These results establish that probe E could be useful in the stu dy of membrane-bound protein topography by the fluorescence-energy-transfer method.