The localization of trypsin in cultured mammalian cells.

The localization of trypsin in HeLa and CBM17 baby mouse kidney cells was studied using fluorescent and electron-microscope autoradiographical techniques. Intracellular uptake of trypsin, as well as cell surface localization, was demonstrated by the use of direct FITCand tritium acetylated-labelled trypsin and immunoreactive procedures. Intracellular penetration of the enzyme was temperature dependent and while evident at 37 and 25 °C was negligible at 4 °C. Higher proteolytic activity could be demonstrated in the supernatants from disrupted trypsin-treated cells than in supernatants from disrupted PBS-treated cultures. Treatment of trypsin with serum, whilst depressing enzyme protease activity, did not modify intracellular uptake of the enzyme and intracellular localization of trypsin persisted in cultured cells for up to about 48 h. The results, while not accounting for the primary event in cell alteration following exposure to trypsin, clearly suggest that consideration must be given to the fact that intracellular penetration of the enzyme may affect certain intrinsic processes of the cell.