Glycoprotein-protein interaction examined by kinetic studies of pyrene transfer.

The transfer of pyrene between alpha 1-acid glycoprotein, acethylcholinesterase and sonicated liposomes was used to monitor glycoprotein-protein interaction on the lipid bilayer. When a density solution of glycoprotein or protein labeled with pyrene was mixed with unlabeled suspension of free-phospholipid liposomes, or suspensions containing the complexes of glycoprotein-lipid, protein-lipid, or glycoprotein-protein-lipid, pyrene excimer fluorescence increased with a half-time of approximately 30--50 msec. Since the increase in excimer fluorescence indicates an increase in the microscope concentrations of pyrene, the observed fluorescence change reflects pyrene transfer. The half-times for the increase in excimer fluorescence were determined in the presence of glycoprotein and protein in the liposomes. On the basis of the determined half-times it was concluded that both, glycoprotein and protein are bound on the lipid bilayer. Our data also suggest that the thickness of the lipid bilayer is significantly changed in this case. The observation suggests strongly that the limiting step in the transfer of pyrene is not the dissociation of pyrene, but the uptake of the pyrene monomers by the lipid phase.