Characterization of a fluorescence assay to monitor changes in the aqueous volume of lipid vesicles.
The fluorescent compound, 4',5'-bis[N,N-bis(carboxymethyl)aminomethyl] fluorescein (calcein) has been characterized for use in lipid vesicle studies. Particularly useful is its reaction with Co2+, which results in fluorescence quenching. This is accompanied by about a 10-nm blue shift in the uv absorbance bands and a small reduction in the visible absorbance band. For vesicle studies, Co2+ may be combined with citrate, which does not significantly hinder calcein quenching by Co2+. It does augment the absorbance of the metal ion. No significant interaction of citrate X Co2+ with phosphatidylserine vesicles was observed. Zn2+ is capable of displacing Co2+ and restoring calcein fluorescence. Fluorescence quenching due to formation of the calcein X Co2+ complex can also be reversed with EDTA. Thus, calcein is the basis of some simple reactions which can be used to assay changes in the aqueous volume of lipid vesicles.
D002021:Buffers; D002614:Chelating Agents; D055598:Chemical Phenomena; D002621:Chemistry; D005452:Fluoresceins; D008081:Liposomes / Q000032:analysis*; D008563:Membrane Lipids; D008670:Metals; D010743:Phospholipids; D013050:Spectrometry, Fluorescence
D002021:Buffers; D002614:Chelating Agents; D005452:Fluoresceins; D008081:Liposomes; D008563:Membrane Lipids; D008670:Metals; D010743:Phospholipids; C007740:fluorexon