Endogenous Cathepsin Activation of Trypsinogen in Extracts of Dog Pancreas.∗

Summary Evidence is presented that endogenous trypsinogen in extracts of dog pancreas is activated under the same conditions that cathepsin B activates trypsinogen in vitro. The activation occurs at pH 3.6 and is enhanced by cysteine and is inhibited by iodoacetic acid. The tentative conclusion reached is that cathepsin B-like enzymes in pancreas are catalyzing the reaction. The possible clinical implications of such reactions is discussed.