Entamoeba histolytica: correlation between virulence and content of proteolytic enzymes.

Intact trophozoites of the virulent Entamoeba histolytica strain HM-1:IMSS (HM-1) destroyed a monolayer of baby hamster kidney (BHK) cells at a higher rate and efficiency than trophozoites of the nonvirulent strain HK-9. The destructive effect could be partially attributed to the proteolytic activity of the amoeba, since quantitative differences were found in the enzymatic activity of the two strains tested. Crude extracts or secreted enzymes of HM-1 trophozoites digested Azocoll, as well as the bovine cold-insoluble globulin fraction, at a much higher rate than the corresponding preparations from HK-9. This proteolytic activity was found to be activated by free sulfhydryl groups. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the BHK cell proteins of pre- and postamoebic activities showed patterns similar to the trypsin effect on the same target cells. These enzymes were found to digest the proteins participating in the attachment of the target cells to the substrate and, consequently, cause detachment of these cells.