Lipocortin-like anti-phospholipase A2 activity of endonexin

Endonexin (protein II, 32.5 kDa) has been purified to homogeneity from bovine liver in the following steps: selective extraction by EGTA from membranes precipitated with Triton X-100/calcium; chromatography on DEAF-TSK 545 at pH 7.0, endonexin being eluted at 0.1 M NaCl; affinity chromatography on polyacrylamide-immobilized phosphatidylserine; gel filtration on TSK 3000. The amino acid composition was essentially similar to that previously reported. Using [3H]oleic acid-labelled Escherichia coli membranes as substrate, endonexin inhibited phospholipase A2 from pig pancreas. Maximal inhibition was 55 and 70%, whereas 50% inhibition occurred at 480 and 120 nM endonexin and lipocortin II, respectively. These data could be related to common features shared by both lipocortins/calpactins and endonexin, i.e. the presence of a consensus sequence and the ability to bind to anionic phospholipids in a calcium-dependent manner.