Polyphosphoinositides Are Present in Plasma Membranes Isolated from Fusogenic Carrot Cells

Fusogenic carrot cells grown in suspension culture were labeled 12 hours with myo-[2-(3)H]inositol. Plasma membranes were isolated from the prelabeled fusogenic carrot cells by both aqueous polymer two-phase partitioning and Renografin density gradients. With both methods, the plasma membrane-enriched fractions, as identified by marker enzymes, were enriched in [(3)H]inositol-labeled phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP(2)). An additional [(3)H]inositol-labeled lipid, lysophosphatidylinositol monophosphate, which migrated between PIP and PIP(2) on thin layer plates, was found primarily in the plasma membrane-rich fraction of the fusogenic cells. This was in contrast to lysophosphatidylinositol which is found primarily in the lower phase, microsomal/mitochrondrial-rich fraction.