title: The bivalent-cation dependence of phosphatidylinositol synthesis in a cell-free system from lymphocytes.
abstract: The bivalent-cation requirements of two enzymes involved in phosphatidylinositol synthesis were defined for pig lymphocyte membranes using a citric acid buffer. CTP:phosphatidic acid cytidylyltransferase (EC 2.7.7.41) is activated by free Mn2+ concentrations above 20nM and by free Mg2+ concentrations above 10 microM. When activated by Mg2+, the enzyme is weakly inhibited by Ca2+ (Ki greater than 250 microM), but Ca2+ has no effect when Mn2+ is used to stimulate CDP-diacylglycerol synthesis. The synthesis of phosphatidylinositol from phosphatidic acid is also stimulated by Mn2+ and Mg2+ concentrations similar to those above and is inhibited by free Ca2+ concentrations above 500nM, probably by its action on CDP-diacylglycerol:inositol 3-phosphatidyltransferase (EC 2.7.8.11). Taken together, these studies suggest that under physiological conditions phosphatidylinositol synthesis is activated by Mg2+ and it is possible that it is further regulated by the free concentrations of Ca2+ and/or Mn2+.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002474:Cell-Free System / Q000187:drug effects; D003567:Cytidine Diphosphate Diglycerides / Q000096:biosynthesis; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology*; D008345:Manganese / Q000494:pharmacology*; D009713:Nucleotidyltransferases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000096:biosynthesis*; D013552:Swine
chemical_list: D003567:Cytidine Diphosphate Diglycerides; D010716:Phosphatidylinositols; D008345:Manganese; D009713:Nucleotidyltransferases; C022348:phosphatidate cytidylyltransferase; D008274:Magnesium; D002118:Calcium