14N NMR of lipid bilayers: effects of ions and anesthetics.
The interaction of divalent and trivalent metal cations, ferricyanide, a lipophilic ion (tetraphenylborate), and a local anesthetic (tetracaine) with the phosphocholine head group of egg lecithin was investigated by using wide-line 14N and 31P NMR. Measurements of the 14N quadrupolar splittings in the presence of a variety of perturbing agents demonstrated that the 14N NMR technique can be used to directly monitor ion or anesthetic binding. The 14N quadrupolar splitting (delta nu Q) is a measure of the order parameter of the C beta-N bond segment, and changes in delta nu Q as large as 3.5 kHz were observed. Moreover, a comparison of the changes in the quadrupolar splittings induced by the binding of ions or anesthetics provided a sensitive method of discriminating between these perturbing agents in their ability to alter the orientational order of the C beta-N bond segment of the phosphocholine moiety. Without exception, addition of metal ions or anesthetics always resulted in a decrease of the 14N delta nu Q. This reduction reflects a change in the average orientation or degree of motional averaging at the C beta-N bond segment position. In the case of metal ion binding, the strength of the interaction increased with the charge of the metal ion in the order Ca2+ less than Ln3+, in agreement with a previous 2H NMR study [Akutsu, H., & Seelig, J. (1981) Biochemistry 20, 7366-7373].(ABSTRACT TRUNCATED AT 250 WORDS)
D000838:Anions; D002412:Cations; D055598:Chemical Phenomena; D002621:Chemistry; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy; D008674:Metals, Rare Earth; D008954:Models, Biological; D008968:Molecular Conformation; D010713:Phosphatidylcholines; D013748:Tetracaine
D000838:Anions; D002412:Cations; D008051:Lipid Bilayers; D008674:Metals, Rare Earth; D010713:Phosphatidylcholines; D013748:Tetracaine