Evidence for the presence of a trypsin inhibitor within rabbit and mouse tumour cells.

Post-granule supernatant fractions obtained from induced tumour cells in rabbits and from Ehrlich ascites tumour cells in mice have been shown to contain a protease inhibitor, inhibiting trypsin (EC 3.4.21.4) and neutral proteases located in the cytoplasm of the cells. This inhibition was found to be irreversible over the time period studied, independent of the time of enzyme incubation and independent of the extent of trypsin digestion within an insoluble substrate (within the limits of linear enzyme kinetics).