The non-parallel increase of amylase, chymotrypsinogen and procarboxypeptidase in the developing chick pancreas

Developmental changes in the levels of α-amylase, procarboxypeptidase and chymotrypsinogen were studied in the pancreas of the chick embryo (developmental age 13-20 days) and the newly-hatched chick (development age 21-23 days). 1. 1.|Levels of zymogens were determined by measuring the activity of the corresponding proteolytic enzyme after activation of the zymogen with trypsin. For this purpose controlled conditions of activation of procarboxypeptidase and chymotrypsinogen were developed which would permit full activation of the zymogens in homogenates of pancreas at different stages of development. 2. 2.|When homogenates of pancreas at different stages of development were mixed, enzyme activities were additive. This seems to rule out the possibility that changing concentrations of inhibitors or activators during development influence the activities of the enzymes studied. 3. 3.|The specific activities of all three enzymes increase most steeply after 18 days of development reaching a maximum in the 1-day chick (22 days of development). However, in spite of this similarity, the level of each enzyme changes with age in a different and characteristic manner. From 13-22 days of development the specific activities of amylase, carboxypeptidase and chymotrypsin increase 9-fold, 24-fold and 200-fold, respectively.