title: Ca(phosphatidate)2 can traverse liposomal bilayers.
abstract: Phosphatidic acid can act as Ca2+ cross-membrane ionophore without the necessity of previous autoxidation. The apparent PA-CA2+ dissociation constant is 3 X 10(-3), i.e., in the range of extracellular Ca2+ concentration. There is at least 100-fold preference for Ca2+ over Mg2+. Ca2+ transfer rates are proportional to the square of phosphatidic acid concentration in the bilayer. Removal of the fatty acid ester CO groups reduces the Ca2+ ferrying rate by more than 90 percent. It appears that the cation is held in a cage formed by phosphate and carbonyl oxygens of two PA molecules. In this coordination complex both Ca2+ and the phosphatidic acid headgroups are dehydrated, and the Ca(phosphatide)2 assembly becomes lipid-soluble and can traverse the bilayer.
mesh_terms: D002118:Calcium / Q000378:metabolism*; D007476:Ionophores; D008051:Lipid Bilayers; D008081:Liposomes / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010712:Phosphatidic Acids / Q000378:metabolism*
chemical_list: D007476:Ionophores; D008051:Lipid Bilayers; D008081:Liposomes; D010712:Phosphatidic Acids; D002118:Calcium