Subcellular distribution and stability of the major hemolytic activity ofEntamoeba histolytica trophozoites

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Abstract
Since the hemolytic activity of extracts fromEntamoeba histolytica trophozoites previously described by us might determine at least partially the necrotic lesions of amebiasis, we have continued its characterization in vitro. Using rat erythrocytes as target cells, we have found that cytolysis byE. histolytica trophozoite extracts was (1) dose dependent, (2) localized mainly in a vesicular fraction whose absolute and specific activities were respectively 1.9 and 4.0 times higher than those of total extracts, (3) maximal at pH 8 in the presence of 1 mM Ca++, and (4) progressively lost by heating at 90°C or repeated freezing and thawing. From these results we infer that the major hemolytic factor ofE. histolytica may be a protein normally neutralized by an intracellular inhibitor or activated during fractionation.