Embryonic and Adult Chymotrypsinogens of Chicken Pancreas

Abstract

BEEF and pig pancreas contain chymotrypsinogens A, B and C, homologous proteins whose activation products have different substrate specificities^1–4. Chymotrypsinogens of the A and B type have been found in several vertebrate species⁵ whereas the C type chymotrypsinogen seemed to be restricted to the pig and cow^2–4. An investigation in this laboratory⁶ showed that chick pancreas secretory granules contain three chymotrypsinogens, called chymotrypsinogens 1, 2 and 3. The specificities of the activation products of chymotrypsinogens 1 and 2 resembled those of bovine chymotrypsinogens B and A respectively ^2,6,7. Because of the small relative amounts of chymotrypsinogen 3 in the extracts, the specificity of its activation product could not be determined with certainty, but some similarities to mammalian chymotrypsin C were detected⁶. As the data of a later investigation⁸ suggested that embryonic chick pancreas might contain relatively large amounts of chymotrypsinogen 3, the chymotrypsinogens in the developing chick pancreas were further studied. This report shows that the specificity of chick embryo chymotrypsin 3 is similar to that of mammalian chymotrypsin C. We also show that chymotrypsinogen 3 is the major chymotrypsinogen species during embryonic development but becomes a minor species after hatching, when chymotrypsinogens 1 and 2 become prominent.