Kinetics of Structural Transitions Induced by pH Changes

Bovine trypsinogen, trypsin and chymotrypsinogen undergo an isomerization in acidic medium, like many other proteins. We have studied the kinetics of these isomerizations by means of pH changes in a stopped‐flow apparatus. The order of magnitude of the rate constants is 20–100 sec‐1. The model used to interpret the effect of pH on kinetics leads to an unequivocal identification of at least one carboxylate group buried in the native form of these proteins. The effects of temperature and ionic strength on the kinetics are described.