A low‐molecular‐mass Kazal‐type protease inhibitor isolated from rat hepatocytes is identical to rat pancreatic secretory trypsin inhibitor II

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Abstract
A low‐molecular‐mass serine protease inhibitor was purified from hepatocytes and liver of rats. It was found to be a single polypeptide of 56 amino acid residues corresponding to Mr= 6224, a value that is in agreement with the molecular mass determined by gel chromatography. The inhibitor formed a complex in a molar ratio of 1:1 with trypsin. Its complete amino acid sequence was identical with that of pancreatic secretory trypsin inhibitor II (PSTI‐II) in pancreatic juice, but not with that of PSTI‐I [Uda, K., Ogawa, M., Shibata, T., Murata, A., Mori, T., Kikuchi, N., Yoshida, N., Tsunasawa, S. & Sakiyama, F. (1988) Biol. Chem. Hoppe‐Seyler 369, 55–61]. PSTIs have been reported to be primarily pancreatic secretory products, but in patients immunoreactive PSTI was found in the plasma and urine during acute inflammatory disease and shown to be produced ectopically in cancer tissues. Here we report for the first time that PSTI‐II is present in other normal tissues besides the pancreas.