title: Binding of calcium to phosphatidylcholines as determined by proton magnetic resonance and infrared spectroscopy.
abstract: The interactions of calcium, magnesium, and the rare earth cations, cerium, neodymium, and praseodymium, with phosphatidylcholines were studied by proton magnetic resonance and infared spectroscopy. The calcium-induced chemical shifts for the various protons of phosphatidylcholine were C alpha choline greater than C beta choline greater than N(CH3)3 greater than C3 glycerol. No significant chemical shifts were observed for the C1 and C2 glycerol protons. None of the acyl chain protons were affected by the presence of calcium. Analysis of the salt-induced chemical shifts yielded binding curves with an excellent fit with the theoretical. The vicinal coupling constants for the various protons of phosphatidylcholine did not appear to change in the presence of calcium. The lanthanide-induced isotropic shifts for the protons of phosphatidylcholines followed the order Cbeta choline greater than C3 glycerol greater than Calpha choline greater than N(CH3)3. Examination of the P=O stretching band (1150-1300 cm-1) of phosphatidylcholines by differential infrared spectroscopy showed that this band shifted to shorter wavelengths in the presence of calcium. The site of calcium binding to phosphatidylcholines as deduced from the proton magnetic resonance and infrared data is discussed in light of the high specificity for calcium in enhancing the amino-catalyzed methanolysis of phosphatidylcholines.
mesh_terms: D001665:Binding Sites; D002118:Calcium; D002563:Cerium; D008274:Magnesium; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D008958:Models, Molecular; D008968:Molecular Conformation; D009354:Neodymium; D010713:Phosphatidylcholines; D011221:Praseodymium; D013055:Spectrophotometry, Infrared
chemical_list: D010713:Phosphatidylcholines; D009354:Neodymium; D002563:Cerium; D008274:Magnesium; D011221:Praseodymium; D002118:Calcium