Polylysine and polyamine stimulation of the phosphatidylinositol kinases of amphibian oocyte membranes

Phosphatidylinositol kinase present in Xenopus laevis oocyte membranes catalyzes the formation of phosphatidylinositol 4-phosphate using phosphatidylinositol and ATP as substrates while the activity of a second enzyme, phosphatidylinositol-4-phosphate kinase, results in the synthesis of phosphatidylinositol 4,5-bisphosphate. Large (Mr greater than 20,000) homopolymers of L-lysine or L-ornithine can stimulate the activity of both of these enzymes by at least 2-fold at 10-20 microM concentrations. Under similar conditions poly-L-arginine fails to stimulate the reaction causing a partial inhibition. Smaller polylysine (25 lysines) or lysine-rich oligopeptides such as one corresponding to the last 14 amino acids of the carboxyl end of c-Ki-ras 2 protein produce appreciable stimulation of phosphatidylinositol but at concentrations of 300-500 microM. Spermine and spermidine at millimolar concentrations also stimulate exogenous phosphatidylinositol phosphorylation. The amino-glycoside antibiotic neomycin has a biphasic effect, stimulating the phosphatidylinositol kinase at concentrations below 0.5 mM and strongly inhibiting at higher concentrations. Polylysine also moderately stimulates the loss of radioactivity of phosphatidylinositol-4-32P] phosphate observed in oocyte membranes. Polylysine and polyornithine do not change the apparent Km for ATP of the phosphatidylinositol kinase but increase the Vmax of the reaction.