Phospholipase A enzymes of Entamoeba histolytica: description and subcellular localization

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.