Specificity of Na+ binding to phosphatidylserine vesicles from a 23Na NMR relaxation rate study.
23Na NMR relaxation rate measurements show that Na+ binds specifically to phosphatidylserine vesicles and is displaced partially from the binding site by K+ and Ca2+ but to a considerably less extent by tetraethylammonium ion. The data indicate that tetraethylammonium ion affects the binding of Na+ only slightly, by affecting the surface potential through its presence in the double layer, without competing for a phosphatidylserine binding site. Values for the intrinsic binding constant for the Na+-phosphatidylserine complex that would be consistent with the competition experiments (and the dependence of the relaxation rate on concentration of free Na+) fall in the range 0.4--1.2 M-1 with a better fit towards the higher values. We conclude that in the absence of competing cations in solution an appreciable fraction of the phosphatidylserine sites could be associated with bound Na+ at 0.1 M Na+ concentration.
D002118:Calcium; D055598:Chemical Phenomena; D002621:Chemistry; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D008567:Membranes, Artificial; D010718:Phosphatidylserines; D011188:Potassium; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D013816:Thermodynamics
D008567:Membranes, Artificial; D010718:Phosphatidylserines; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D011188:Potassium; D002118:Calcium