Measurement of the Proteinase Inhibitors of the Bovine Pancreas by Radioimmunoassay

Abstract

Bovine pancreas contains two polypeptide trypsin inhibitors that are not homologous and differ in their inhibitory activity towards chymotrypsin, kallikrein, elastase, and other serine proteinases. The Kunitz inhibitor and the Kazal inhibitor are present in approximately equimolar concentrations in bovine pancreatic tissue, yet only the Kazal inhibitor is detectable in the pancreatic juice. The Kazal inhibitor has been named the pancreatic secretory trypsin inhibitor, PSTI because its concentration in the pancreatic juice parallels that of the exocrine secretory proteins. The Kunitz inhibitor is considered the intracellular inhibitor, however, no direct information is available concerning the intracellular localization of these inhibitors in the pancreas. The preparation of /sup 125/I-labeled derivatives of Kazal and Kunitz inhibitors by the lactoperoxidase method and a radioimmunoassay for each inhibitor are described.