ABSTRACT
The major proteolytic enzyme isolated from soluble fractions of the pathogenic strain HM1: IMSS of Entamoeba histolytica exhibits the properties of a typical cysteine proteinase (Scholze and Schulte, 1988). It has a molecular weight of 27 kDa, an isoelectric point of about 5, an optimal activity against azocasein in a mildly acidic range with maximum activity at pH 4.5. The N-terminal amino acid sequence determined by automated Edman degradation (Schulte and Scholze, 1989) shows homology to papain and cathepsins B, H and L, as well as to another cysteine proteinase isolated from E. histolytica, histolysin (Luaces and Barrett, 1988). It is not yet clear whether the two amoebic proteinases are identical; however, in view of the homology of the enzyme described here to the papain-like cysteine proteinases we propose to name it amoebapain. Since amoebapain is active against native type I collagen from human skin as well as against the extracellular matrix proteins fibronectin and laminin, it has properties consistent with it being a cytotoxin.
