The localization of PI and PIP kinase activities in the sea urchin egg and their modulation following fertilization

Phosphatidylinositol phosphate (PIP) kinase activity is localized to the cortical region of unfertilized sea urchin eggs, while phosphatidylinositol (PI) kinase activity is found in both cortical and noncortical membranes. Following fertilization PIP kinase activity decreases, while PI kinase activity remains unchanged. The selective loss of PIP kinase activity is related to cortical granule exocytosis since the drop in activity does not occur if exocytosis is prevented by high hydrostatic pressure. When isolated cortices are exposed to elevated concentrations of calcium, both the PI and PIP kinase activities increase, suggesting that activation of these enzymes might occur when calcium levels increase within the fertilized egg prior to cortical granule exocytosis. The polyamine spermine also stimulates the formation of phosphatidylinositol bisphosphate at physiological concentrations.