title: Binding of propranolol and gentamicin to small unilamellar phospholipid vesicles. Contribution of ionic and hydrophobic forces.
abstract: Binding of propranolol and gentamicin to small unilamellar phospholipid vesicles having different surface charges was studied at pH 4.4 using an ultra-centrifugation method, and the results were analyzed by an equation describing the Langmuir adsorption isotherms. Gentamicin, a polycationic drug, bound to negatively-charged small unilamellar vesicles composed of 60% phosphatidylcholine and 40% of either phosphatidylinositol, phosphatidylglycerol or phosphatidylserine in a manner consistent with a single class of binding sites but did not bind at all to small unilamellar vesicles of phosphatidylcholine alone. In contrast, propranolol bound readily to both neutral and negatively-charged liposomes in a manner consistent with two types of binding sites. Based on the binding parameters calculated from replots, it is suggested that the high-affinity site is probably at the surface of the liposome and that ionic forces are primarily responsible for this binding. The low-affinity, high-capacity binding site for propranolol was demonstrated with both neutral and negatively-charged liposomes and appeared to be independent of the surface charge. Gentamicin, which is not hydrophobic, did not bind to the low-affinity site. It is hypothesized that hydrophobic interactions are the driving force for propranolol binding to the low-affinity site which may be the interior of the lipid bilayer.
mesh_terms: D001665:Binding Sites; D005839:Gentamicins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007474:Ion Exchange; D008081:Liposomes / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011433:Propranolol / Q000378:metabolism*
chemical_list: D005839:Gentamicins; D008081:Liposomes; D010743:Phospholipids; D011433:Propranolol