Characterization of several phospholipase activities and diacylglycerol/2-monoacylglycerol lipases in rat alveolar macrophages.
We measured phospholipase activities in both the microsomal and the cytosolic enriched fractions of rat alveolar macrophages by using exogenous arachidonic acid-labeled phospholipids. The microsomal fractions contain a neutral calcium-independent phospholipase A2 (PLA2) which acts on substrates phosphatidylcholine (PC) and phosphatidylinositol (PI), a calcium-independent PLA2 acting on phosphatidylethanolamine (PE), and a neutral calcium-dependent PI-specific PLC. The cytosolic fractions contain calcium-dependent phospholipase: PLA2 that hydrolyses PC at alkaline pH, and a neutral PI-specific phospholipase C (PLC). The largest release of arachidonic acid from PI occurred with the cytosolic fractions at pH 6 in the presence of calcium. That hydrolysis involved a PLA2, and a PLC followed by the action of a diacyglycerol and 2-monoacylglycerol lipases. The cytosol also contains a calcium-independent PLA2 acting on PE. Our investigation shows that rat alveolar macrophages possess a number of phospholipases, as well as diacylglycerol and 2-monoacylglycerol lipases. The above enzymes could play an essential role in the remodeling of membrane phospholipids in resting cells, and the generation of physiologically active lipids in activated cells.
Errasfa
M
M
Department of Preventive Medicine, Harvard Medical School, Massachusetts General Hospital, Boston 02114.
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008264:Macrophages / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008994:Monoacylglycerol Lipases / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D011650:Pulmonary Alveoli / Q000166:cytology; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
D001095:Arachidonic Acids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010716:Phosphatidylinositols; D010740:Phospholipases; D008994:Monoacylglycerol Lipases; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2; D002118:Calcium