Entamoeba histolytica and E. invadens: Sulfhydryl‐Dependent Proteolytic Activity1

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Abstract
Sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME) activate proteolytic enzymes present in extracts of E. histolytica and E. invadens; SDS (0.5%) and 2-ME (1.4 and 715 mM) doubled the enzymatic activity when assayed on a stained insoluble substrate. Urea (4 M) did not reduce this activity, suggesting that amoebic proteases are stable in the above denaturant conditions. Specific reagents for SH groups completely inhibited proteolytic activity regardless of pH. Inhibition with alkylating agents, such as N-ethylmaleimide and iodoacetamide, was reversed with 715 mM 2-ME as was also observed with papain. The main proteolytic enzymes contained in extracts of E. histolytica and E. invadens may be dependent on free thiol groups.