Biochemical and electron microscopic observations of cytotoxic effect of a fraction from hemolytic streptococcus on Ehrlich ascites carcinoma cells.

A protein fraction (60-F), obtained from cell-free extract of living hemolytic streptococcus, Su-strain, by 50-60% saturation with ammonium sulfate, inhibited the de novo synthesis of nucleic acids and proteins in Ehrlich ascites carcinoma (EAC) cells. 60-F released RNA but not DNA from EAC cells. This cytotoxic or cytolytic effect of 60-F was substantiated morphologically by scanning and transmission electron microscopic (SEM and TEM) observations, showing that 60-F induced cellular changes such as a loss of microvilli, bleb formation, cell deformity and partial gap of cell membrane in EAC cells. In addition, it was found that 60-F was more stable in RPMI-1640 medium supplemented with fetal calf serum than in other various media examined and was sensitive to temperature, pH changes and trypsin digestion.