Phospholipase A Enzymes of Entamoeba histolytica: Description and Subcellular Localization

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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 (10−3M), Rosenthal's inhibitor (dimethyl-dl-2,3-distearoylpropyl-2′-hydroxyethyl ammonium acetate; 10−4M), quinacrine (10−4M), and hydrocortisone (10−4M). Calcium-independent phospholipase A activity was inhibited by Rosenthal's inhibitor (10−4M) and quinacrine (10−3M). 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. histotytica.

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