Membrane Translocation Assayed by Fluorescence Spectroscopy

Assessing the ability of biomolecules or drugs to overcome lipid membranes in a receptor-independent way is of great importance in both basic research and applications involving the use of liposomes. A combination of uptake , release , and dilution experiments performed by steady-state fluorescence spectroscopy provides a powerful, straightforward, and inexpensive way of monitoring membrane translocation of fluorescent compounds. This is particularly true for peptides and proteins carrying intrinsic tryptophan residues, which eliminates the need for attaching extrinsic labeling moieties to the compound of interest. The approach encompasses three different kinds of fluorescence titrations and some simple calculations that can be carried out in a spreadsheet program. A complete set of experiments and data analyses can typically be completed within two days.