Characterization ofa Polyphosphoinositide Phospholipase CfromthePlasmaMembraneofAvenasativa

Aphosphoinositide-specific phospholipase Cactivity wasidentified inoatroot(Avena sativa, cvVictory) plasma membranes purified byseparation inanaqueous two-phase polymer system. Theenzymeishighly active towardinositol phospholipids but onlyminimally active towardphosphatidylethanolamine and phosphatidylcholine. Activity approaches maximal levels at200 micromolar phosphatidylinositol 4-phosphate (PIP) andishighly dependent oncalcium; itisinhibited byImillimolar EGTAandis activated bycalcium withanapparent activation constant of2 micromolar. At10micromolar calcium and200micromolar inositol phospholipid, theenzymeisspecific forphosphatidylinositol 4,5