Phosphatidylinositol cleavage in lymphocytes. Requirement for calcium ions at a low concentration and effects of other cations.
The soluble activity in lymphocytes which converts phosphatidylinositol into 1,2-diacylglycerol and inositol phosphates requires Ca(2+) ions. At pH7 maximum activity occurs at [Ca(2+)](free) approximately 0.7mum whereas at pH5.5 the equivalent value is approx. 50mum. At [Ca(2+)](free) approximately 1mum, a concentration similar to common intracellular values, essentially all activity is confined to the peak of activity at pH7.0. Previous reports of requirements for larger amounts of Ca(2+) may reflect the fact that the Ca(2+)-buffering capacity of phosphatidylinositol means that high substrate concentrations can effectively decrease [Ca(2+)](free). Cations which displace Ca(2+) from association with phosphatidylinositol can, at low [Ca(2+)](free), enhance enzyme activity. Phosphatidylinositol breakdown in intact cells might be controlled, at least in part, by changes in intracellular [Ca(2+)](free).
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D013552:Swine
D010716:Phosphatidylinositols; D004533:Egtazic Acid; D011189:Potassium Chloride; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium