Fluorescence quenching in model membranes. 1. Characterization of quenching caused by a spin-labeled phospholipid.

A new method is described to evaluate contact between fluorophors and lipids in model membranes. This method utilizes a nitroxide spin-labeled phosphatidylcholine to quench th fluorescence from a variety of membrane-bound molecules by a static process. The distance dependence of the fluorescence quenching is analyzed in terms of simple models. The analysis shows that quenching of diphenylhexatriene, p-terphenyl, and molecules containing tryptophan arises only from spin-labeled phospholipid that is in contact with the fluorophor.