Possible lysosomal activation of pancreatic zymogens. Activation of both human trypsinogens by cathepsin B and spontaneous acid. Activation of human trypsinogen 1.

Human trypsinogens 1 and 2 were activated at the same rate by pure human cathepsin B at pH 3.8. Human trypsinogen 1 was also spontaneously activated during incubation at acidic pH, activation being most rapid at pH 5.0. In contrast, trypsinogen 2 showed little or no activation under these conditions. The presence of calcium salts (20mM) delayed the onset of activation under all conditions tested. These findings support the proposal that premature activation of the pancreatic zymogens may result from their entry into the lysosomal system in pancreatitis.