Trypsin Inhibitor from Human Pancreas and Pancreatic Juice

Abstract

Abstract Human pancreatic secretory trypsin inhibitor has been isolated in 55% yield from human pancreatic juice and in 45% yield from human post mortem pancreata by gel filtration on Sephadex G-75 in the presence of 10-4 m diisopropyl phosphofluoridate and by ion exchange chromatography on DEAE-cellulose and SP-Sephadex. The polypeptide inhibitor has a molecular weight of 6242 and contains 56 amino acid residues per molecule: Asp3, Asn5, Thr4, Ser3, Glu4, Gln2, Pro3, Gly5, Ala1, Cys6, Val2, Ile3, Leu4, Tyr3, Phe1, Lys4, and Arg3 and does not contain glucosamine or galactosamine. The inhibitor was isolated as five chromatographic forms with identical amino acid content, specific activity for trypsin inhibition and molecular weight on sodium dodecyl sulfate gel electrophoresis. All forms of the inhibitor are homogeneous by acrylamide gel electrophoresis, amino acid analysis, and on the basis of the stoichiometry of their interaction with trypsin. All of the three forms subjected to Edman degradation had Asx-Ser as their NH2-terminal residues. The multiple chromatographic forms could be distinguished on the basis of chromatographic behavior on ion exchange resins, by acrylamide gel electrophoresis and, for the three major forms, on the basis of amide content and susceptibility to enzymatic digestion. It is concluded that the multiple chromatographic forms differ in amide content. The inhibitor is secreted in the pancreatic juice in the free form (not combined with trypsin) in an amount equivalent to 0.1 to 0.8% of the total protein in pancreatic juice. The inhibitor is of the Kazal type and similar to the pancreatic secretory trypsin inhibitors isolated from pancreatic juice of other species. The human inhibitor is the only pancreatic secretory trypsin inhibitor studied which effectively inhibits human cationic trypsin.