Human fibroblasts contain a proteolytic activity which is inhibited by the Bowman-Birk protease inhibitor.

The Bowman Birk protease inhibitor (BBI) has been shown to be an effective suppressor of carcinogenesis in vivo and in vitro. In this report we demonstrate that normal human fibroblasts and Bloom cells contain a BBI-inhibitable proteolytic activity. The enzyme cleaves gelatin, has a molecular mass of 43 kDa, and is located in the cytosol. This activity has maximal activity at pH 8 and was inhibited by diisopropylfluorophosphate but was not affected by EDTA or 1,10-phenanthroline, indicating that this enzyme is a serine protease. We have reported previously that a similar BBI-inhibitable activity is present in C3H/10T1/2 mouse embryo fibroblast cells. Our results suggest that a common "target enzyme" of the BBI is present in mouse and human cells.