title: Phospholipase A enzymes of Entamoeba histolytica: description and subcellular localization.
abstract: Cytolysis of target cells by Entamoeba histolytica is a rapid, contact-dependent event that appears to involve calcium and amebic phospholipase A enzymes. There are two phospholipase A enzymes of E. histolytica: one calcium independent and optimally active at an acid pH, and a second calcium dependent and most active at an alkaline pH. The amebic calcium-dependent enzyme was inhibited by pharmacological antagonists that have been shown to reduce cytolysis of target cells by intact amebae: phosphatidylcholine (10(-3) M), Rosenthal's inhibitor (dimethyl-dl-2,3-distearoylpropyl-2'-hydroxyethyl ammonium acetate; 10(-4) M), quinacrine (10(-4) M), and hydrocortisone (10(-4) M). Calcium-independent phospholipase A activity was inhibited by Rosenthal's inhibitor (10(-4) M) and quinacrine (10(-3) M). The calcium-dependent phospholipase A enzyme is highly associated with plasma membrane fractions; the calcium-independent enzyme is predominantly found in soluble fractions. These findings further suggest an association of calcium-dependent phospholipase A activity with cytolytic activity of E. histolytica.
authors.forename: S A
authors.initials: SA
authors.lastname: Long-Krug
authors.forename: K J
authors.initials: KJ
authors.lastname: Fischer
authors.forename: R M
authors.initials: RM
authors.lastname: Hysmith
authors.forename: J I
authors.initials: JI
authors.lastname: Ravdin
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D004748:Entamoeba histolytica / Q000201:enzymology* / Q000254:growth & development / Q000648:ultrastructure; D006854:Hydrocortisone / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D010713:Phosphatidylcholines / Q000494:pharmacology; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011796:Quinacrine / Q000494:pharmacology; D013228:Stearates / Q000494:pharmacology; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D010713:Phosphatidylcholines; D013228:Stearates; C015161:Rosenthal's inhibitor; D010740:Phospholipases; D010741:Phospholipases A; D011796:Quinacrine; D002118:Calcium; D006854:Hydrocortisone