Fig. 4.

Mutations L81A and R122A stabilize cationic trypsin against chymotrypsin C-mediated degradation. Wild-type, L81A, and R122A cationic trypsins were incubated at 2 μM concentration with 300 nM chymotrypsin C in 0.1 M Tris·HCl (pH 8.0) and 25 μM CaCl₂ (final concentrations). (A) At the indicated times, residual trypsin activity was measured as described in Fig. 1A. (B and C). Aliquots (100 μl) were precipitated with 10% trichloroacetic acid (final concentration) and analyzed by SDS/15% PAGE under reducing conditions.