title: An intramolecular excimer forming probe used to study the interaction of alpha-lactalbumin with model membranes.
abstract: The nonconjugated bichromophoric molecule 1,3-di(1-pyrenyl)propane shows, besides the pyrene monomer fluorescence, a structureless emission due to an intramolecular excited dimer (excimer). In the case of intramolecular excimer forming systems, the ratio of the emission intensities of excimer vs. monomer (IE/IM) is sensitive to changes in membrane structure as will be illustrated here. The present molecule is a useful probe to report on lipid-protein interactions, at least in our model system. We have introduced it into the hydrocarbon layer of dimyristoylphosphatidylcholine vesicles in order to study their interaction with alpha-lactalbumin (alpha-LA) as a function of pH and temperature. On the basis of steady-state fluorescence, kinetic, and energy transfer studies, we have found that, at pH 4, alpha-LA strongly interacts with the lipid bilayer. In steady-state fluorescence experiments, changes of the ratio IE/IM and shifts of the transition temperature have been observed, reflecting changes of membrane structure caused by interaction with alpha-LA. Kinetic studies of the rate of interaction of alpha-lactalbumin and measurements of energy transfer from excited tryptophan(s) to the fluorescent probe confirm the steady-state experiments. Our results agree with previously reported microcalorimetric, gel chromatographic, and fluorescence polarization studies.
mesh_terms: D000818:Animals; D002417:Cattle; D004134:Dimyristoylphosphatidylcholine; D005260:Female; D007700:Kinetics; D007768:Lactalbumin; D008081:Liposomes; D008892:Milk; D010713:Phosphatidylcholines; D011485:Protein Binding; D011721:Pyrenes; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D008081:Liposomes; D010713:Phosphatidylcholines; D011721:Pyrenes; C035116:1,3-di-(1-pyrenyl)propane; D007768:Lactalbumin; D004134:Dimyristoylphosphatidylcholine