Phosphatidylinositol cleavage in lymphocytes: requirement for calcium ions at a low concentration and effects of other cations

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Colleges, School and Institutes


The soluble activity in lymphocytes which converts phosphatidylinositol into 1,2 diacylglycerol and inositol phosphates requires Ca2+ ions. At pH7 maximum activity occurs at [Ca2+]free 0.7 μM whereas at pH5.5 the equivalent value is approx. 50 μM. At [Ca2+]free μM, 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 Ca2+ may reflect the fact that the Ca2+ buffering capacity of phosphatidylinositol means that high substrate concentrations can effectively decrease [Ca2+]free. Cations which displace Ca2+ from association with phosphatidylinositol can, at low [Ca2+]free enhance enzyme activity. Phosphatidylinositol breakdown in intact cells might be controlled, at least in part, by changes in intracellular [Ca2+]free.


Original languageEnglish
Pages (from-to)599-604
Number of pages6
JournalBiochemical Journal
Issue number3
Publication statusPublished - 1 Jan 1974