Bovine pancreatic trypsin inhibitor and related isoinhibitors in bovine liver. A biochemical and histochemical study

A Kunitz-type inhibitor family has been biochemically and histochemically characterized in bovine liver. This family includes the well-known pancreatic trypsin inhibitor (BPTI) and three BPTI-related molecular forms (isoinhibitors I, II and III). The purification of the inhibitors was performed by affinity chromatography on immobilized trypsin followed by fast protein liquid chromatography. The inhibitors were identical to those identified previously in bovine spleen and lung. Light immunohistochemical experiments were done by a streptavidin-biotin-peroxidase method using two different immunoglobulin preparations, which selectively discriminated between BPTI and the other isoinhibitors. BPTI-related immunoreactivity was found exclusively at the level of isolated cells, of which many were identified as mast cells by toluidine blue staining. By contrast, isoinhibitor-related immunoreactivity showed a more widespread distribution, including hepatocytes, mast cells and biliary duct epithelial cells. Finally, specific immunoreactivity was also present in plasma. These results suggest that: i) BPTI and related isoinhibitors may be involved in the regulation of the activity of some mast cell proteases, as it happens in other bovine organs (Businaro et al. 1987, 1988); ii) BPTI isoinhibitors, but not BPTI itself, may also control proteolytic activities in hepatic specific structures (hepatocytes and biliary duct epithelial cells).