The present study identifies the phosphorylation sites of the 85-kDa cytosolic phospholipase A 2 (cPLA 2)inhuman platelets and HeLa cells. Tryptic digests of 32 P-phosphorylated and-immunoprecipitated cPLA 2 were analyzed by microbore high performance liquid chromatography and two-dimensional phosphopeptide mapping against synthetic phosphopeptide standards. Thrombin stimulated significant phosphorylation of platelet cPLA 2 at two sites, Ser-505 and Ser-727. Exclusive phosphorylation on these two sites was also seen in collagen-stimulated platelets and HeLa cells stimulated with interferon- � or arsenite; no tyrosine phosphorylation was detected. The inhibitor of the 38-kDa stressactivated protein kinase (p38 mapk), SB 203580, reduced phosphorylation of both Ser-505 and Ser-727 by 50 an
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