Enzymic Proteolysis byEntamoeba histolytica; biochemical characteristics and relationship with invasiveness

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Abstract
The proteolytic activity of extracts ofEntamoeba histolyticahas been further investigated. Casein and gelatin, but not haemaglobin, were hydrolysed. Activity was observed in the pH range 5·8 to 8·5 with optimal activity at pH 7·5 to 7·9. Activity was optimal at 37° C. and sulphydryl groups were not required. Concomitant bacteria showed no proteolytic activity. Hyaluronidase, collagenase and lecithinase could not be detected.An inhibitor of proteolytic enzyme was present in sera of all animals tested and in egg yolk. All culture media prepared from eggs were inhibitory, but inspissation or dilution of serum inactivated the serum inhibitor. Purified trypsin inhibitors from lima and soy bean were not active against the amoebic enzyme. Proteolytic enzymes were not secreted extracellularlyin vitro.High proteolytic activity was found in two out of five invasive, freshly isolated, strains ofE. histolyticaand after two series of liver passages of a single strain. The significance of these observations is discussed. It is concluded that the present evidence does not convincingly demonstrate that high proteolytic activity is required for tissue invasion by amoebae, but may accompany another factor.