Effect of activation peptide mutations on autoactivation of human cationic trypsinogen. Approximately 2 μM wild-type or mutant trypsinogen (final concentration in a final volume of 100 μl) was incubated at 37°C, in 0.1 M Tris-HCl (pH 8.0) with no Ca²⁺ added (A) or with 1 mM CaCl₂ (B) or in 0.1 M Na-acetate buffer (pH 5.0) in the presence of 2 mg/ml bovine serum albumin (C). Aliquots of 2.5 μl were withdrawn from reaction mixtures at indicated times and trypsin activity was determined with the synthetic substrate N-CBZ-Gly-Pro-Arg-p-nitroanilide. Activity was expressed as percentage of the potential total activity, as determined on similar zymogen samples activated with enteropeptidase