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.
|Number of pages||6|
|Publication status||Published - 1 Jan 1974|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology