title: Calcium association with phosphatidylserine. Modification by cholesterol and phosphatidylcholine in monolayers and bilayers.
abstract: We have examined the association of Ca2+ with phosphatidylserine/cholesterol and phosphatidylserine/dimyristoylphosphatidylcholine mixed monolayers using a surface radiocounting technique. No Ca2+ association with pure monolayers of the uncharged molecules was observed. The Ca2+/phosphatidylserine surface ratio was approximately 1:2 in expanded monolayers of the pure anionic lipid and in phosphatidylserine/phosphatidylcholine mixtures. An increase in surface-associated Ca2+ to a number ratio of 1:1 was observed in phosphatidylserine/cholesterol films when the mole fraction of cholesterol was raised to 0.5 and above and the phospholipid number density held constant. We interpret these findings as a prevention of intermolecular salt formation by the sterol. Further support is provided by particle electrophoresis.
mesh_terms: D002118:Calcium; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002784:Cholesterol; D004586:Electrophoresis; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010718:Phosphatidylserines
chemical_list: D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D002784:Cholesterol; D002118:Calcium