EDTA-insensitive deacylation of phosphatidylinositol in porcine platelet membranes.
Pathways for EDTA-insensitive degradation of phosphatidylinositol (PI) were investigated in porcine platelet membranes and cytosol. The incubation of platelet membranes with [3H]glycerol-labeled PI in the presence of 2mM EDTA produced [3H]lysoPI and aqueous radioactive products, but not radioactive neutral lipids. The degradation in the membranes was optimal at pH8.0-9.0, while EDTA-insensitive hydrolysis was also observed in cytosol with optimal pH at pH7.0-9.0. The major water-soluble product was identified as glycerophosphoinositol. Under the conditions, [14C]arachidonate was released from 1-stearoyl-2-[14C]arachidonyl PI without accumulation of [14C]lysoPI. The deacylation activity preferred PI to phosphatidylcholine and phosphatidylethanolamine. Collectively, these results suggest that PI can be converted to lysoPI by phospholipase A2 in the absence of free Ca2+, providing the substrates for lysoPI-specific phospholipase C characterized earlier in porcine platelet membranes (Murase and Okuyama (1985) J.Biol.Chem. 260, 262-265).
Ueda
H
H
Department of Biological Chemistry, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.
Kobayashi
T
T
Kishimoto
M
M
Tsutsumi
T
T
Okuyama
H
H
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology*; D006868:Hydrolysis; D066298:In Vitro Techniques; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D013552:Swine; D014316:Tritium
D010716:Phosphatidylinositols; D010743:Phospholipids; D014316:Tritium; D004492:Edetic Acid