Trypsin Inhibitor from Bovine Pancreatic Juice

From the ¹ From the Biology Department, Brookhaven National Laboratory, Upton, New York 11973

A trypsin inhibitor has been isolated in 54% yield from bovine pancreatic juice by gel filtration on Sephadex G-75 at pH 8.1 and by elution chromatography on DEAE-cellulose at pH 9.0. It appears to be homogeneous by equilibrium chromatography, equilibrium sedimentation ultracentrifugation, and amino acid analysis, and on the basis of the stoichiometry of its interaction with trypsin. The polypeptide inhibitor has a molecular weight of 6155 and has the following amino acid composition: Asp₇, Thr₄, Ser₂, Glu₇, Pro₄, Gly₅, Ala₁, Cys₆, Val₄, Met₁, Ileu₃, Leu₄, Tyr₂, Lys₃, and Arg₃.

The inhibitor is secreted in the pancreatic juice in the free form (not in a complex with trypsin) and it prevents the trypsin-catalyzed activation of the proteolytic zymogens. The amount of inhibitor is equivalent to 1% of the total potential trypsin in pancreatic juice.

Although two trypsin inhibitors have been isolated from acid extracts of the gland, only one (Kazal type) is present in the secretion. This suggests that the inhibitors are segregated at the subcellular level in the pancreatic acinar cells.

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