Cationic factors affecting phospholipase activities from human lung

Abstract

1 The effects of varying H⁺ and other cation concentrations on phospholipase activity were investigated on two particulate fractions from human lung, corresponding to the mitochondrial and microsomal fractions. 2 Three ¹⁴C-labelled substrates, arachidonyl-phosphatidylcholine (PC), -phosphatidylethanolamine (PE) and -phosphatidylinositol (PI) were used. 3 For two substrates, PE and PI, hydrolysis was maximal at pH 6, with either subcellular fraction. 4 Hydrolysis of all three substrates was strongly inhibited by EDTA and EGTA (10–25 mm). Addition of 2,2-dipyridyl, o-phenanthroline, 8-hydroxyquinoline or desferrioxamine (10 μm-1 mm) did not inhibit but often increased hydrolysis of all substrates. 5 Addition of Zn²⁺, as ZnCl₂, (10 μm-1 mm) inhibited PE and PI, but not PC, hydrolysis. 6 The phospholipase activities from human lung appear to be dependent on Ca²⁺ for maximal activity and to be inhibited by other metal ions including Zn²⁺.