Enzymatic properties of human cytosolic phospholipase A2γ

Abstract

The enzymatic properties of cytosolic phospholipase A2γ (CPLA2γ), an isoform of 85-kDa group IV CPLA 2α: (CPLA2α) were studied I'M vitro and when the enzyme was expressed in cells. CPLA2γ expressed in Sf9 cells is associated with membrane. Membranes isolated from [3H] arachidonic acid-labeled Sf9 cells expressing cPLA2γ, constitutively release [3H]arachidonic acid. The membrane-associated activity is inhibited by the group TV PLA2 inhibitor methylarachidonyl fluorophosphonate, but not effectively by the group VI PLA2 inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H- tetrahydropyran-2-one. CPLA2γ has higher lysophospholipase activity than PLA2 activity. Purified His-cPLA2γ does not exhibit phospholipase A1 activity, but sequentially hydrolyzes fatty acid from the sn-2 and sn-1 positions of phosphatidylcholine. CPLA2γ overexpressed in HEK293 cells is constitutively active in isolated membranes, releasing large amounts of oleic, arachidonic, palmitic, and stearic acids; however, basal fatty acid release from intact cells is not increased. CPLA2α overexpressed in lung fibroblasts from cPLA2α-deficient mice is activated by mouse serum resulting in release of arachidonic, oleic, and palmitic acids, whereas overexpression of cPLA2α results primarily in arachidonic acid release. © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.