Factors that regulate the activity of the phosphatidylinositol kinase present in oocyte membranes of Xenopus laevis.

1. Phosphatidylinositol kinase present in the membranes of Xenopus laevis oocytes was characterized. 2. The enzyme requires Mg2+ or Mn2+ at 10 mM and exogenous phosphatidylinositol (50 microM) increases the formation of phosphatidylinositol-4-phosphate. 3. The oocyte phosphatidylinositol kinase cannot use GTP as a phosphate donor but this compound inhibits competitively the utilization of ATP. 4. Addition of phosphatidylserine and phosphatidylinositol-4,5-bisphosphate stimulates the phosphorylation of phosphatidylinositol but 2,3-bisphosphoglycerate at 5 mM concentration is a strong inhibitor of the reaction.