Characteristics of phospholipase C present in membranes of Xenopus laevis oocytes. Stimulation by phosphatidic acid.

1. Phospholipase C activity present in the membranes of Xenopus laevis oocytes has been studied. 2. These membranes contain an activity capable of hydrolyzing phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate. 3. Hydrolysis of PtdIns 4,5-P2 is absolutely dependent on the presence of Ca2+, however, the hydrolysis of PtdIns occurs in the absence of Ca2+ but addition of the cation stimulates the reaction. 4. Spermine, spermidine and polylysine cause significant stimulation of the phospholipase C activity. 5. Phosphatidic acid causes approximately a 2-fold stimulation of the hydrolysis of both PtdIns and PtdIns 4,5-P2. With PtdIns as substrate, this stimulatory effect of phosphatidic acid is specific and reaches a maximum at a 400 microM concentration.