Electron probe analysis and biochemical characterization of electron-dense granules secreted by Entamoeba histolytica

The interaction of Entamoeba histolytica with collagen induces the intracellular formation and release of electron-dense granules (EDGs) containing collagenase activity which are important in the pathogenicity of this parasite. Purified EDGs contain at least 25 polypeptides with acidic pIs, nine gelatinase activities, small molecules, including inorganic phosphate (Pi), pyrophosphate (PP) and other elements, including Na, Mg, S, Cl, K, Ca and Fe as measured by scanning transmission electron microscopy. Six of these polypeptides with apparent molecular weights of 108, 106, 104, 97, 68 and 59 kDa and two protease activities with apparent molecular weights of 40 and 85 kDa were detected exclusively in the EDGs and were not observed in total trophozoite extracts. Actin was also detected in the EDGs. Therefore, EDGs are a complex of mainly cationic proteins, which contains numerous proteolytic activities, actin and small molecules such as P(i), PP and cations.