Selective 1H-NMR relaxation investigations of membrane-bound drugs in vitro. 2. Angiotensin II.

Binding interactions between human angiotensin II and dipalmitoylphosphatidylcholine bilayer vesicles have been detected by measuring the selective proton spin-lattice relaxation rates of aromatic protons within the peptide. Involvement of the imidazole moiety of the His-6 residue has been demonstrated by the pH dependence of the NMR observables. A lower limit of the binding constant has been evaluated at 78.12 mol-1 dm3 for the interaction involving nonionic intermolecular forces between aromatic residues and the lipid matrix.