Effects of trypsin on protein synthesis in macrophages

Treatment of rabbit alveolar macrophages with crystalline trypsin (0.04–2 mg/10⁸ cells) inhibits protein synthesis and results in increased leakage of cell proteins. Trypsinization does not significantly decrease cellular DNA content or viability, and it does not increase protein breakdown.Trypsin treatment results in decreased oxidation of [1-¹⁴C]glucose and [6-¹⁴C]glucose, and also a decrease in ATP content. Trypsinization also causes a depression of net leucine transport and a reduction in the translational activity of polyribosomes.When normal and trypsinized macrophages are preincubated at 37 °C for several hours and then pulse-labelled with radioactive leucine, protein synthesis is stimulated to approximately the same extent in both the control and the enzyme-treated cells. Since the trypsinized cells still exhibit depressed protein synthesis, this suggests that the inhibition cannot be readily reversed.Indirect evidence indicates that the inhibition of protein synthesis is not due to entry of trypsin into the cells and suggests that the inhibition is due to changes in metabolism resulting from the action of the enzyme at the cell surface.