Processing of pro-colipase and trypsinogen by pancreatic dipeptidyl peptidase IV.

Purified dipeptidyl peptidase IV from porcine pancreas or from human placenta cleaves N-terminal dipeptides from two proteins of the pancreatic juice, namely trypsinogen and pro-colipase. Phenylalanyl-proline is very effectively released (Km approximately 50 microM) from bovine or porcine trypsinogen. Both purified dipeptidyl peptidases also rapidly cleave valyl-proline from the N-terminus of porcine pro-colipase. This degradation does not increase the colipase activity of the precursor. However, under certain conditions, which are not fully understandable at present, dipeptidyl peptidase IV releases more slowly a second dipeptide, aspartyl-proline, from pro-colipase, and this results in a partial activation. Dipeptidyl peptidase IV apparently lines the excretory ducts of porcine pancreas and, therefore, is in close contact to the proteins of pancreatic juice in vivo. The possible significance of these degradations is discussed.