Proteases Occurring in the Cell Membrane: A Possible Cell Receptor for the Bowman-Birk Type of Protease Inhibitors1

The legume-derived Bowman-Birk trypsin and chymotrypsin protease inhibitors (BBI) are effective anticarcinogens in vivo and in vitro. The chymotrypsin-inhibitory domain has been shown to be responsible for this anticarcinogenic action. In this study we identify hydrolytic enzymes by their ability to hydrolyze the relatively specific chymotrypsin substrate succinyl-Ala-Ala-Pro-Phe-aminomethyl coumarin. Results presented in this study show: (a) there is an approximately 2-fold increase in the activity of these enzyme(s) between normal and transformed C3H/10T1/? cells; (b) there are five such enzymes associated with transformed cells (separated by diethylaminoethyl-cellulose chromatography); (c) only two of these enzymes are inhibited by BBI; (</)the BBI-inhibitable enzymes are membrane associated; (e) the BBI-inhibitable enzymes are similar to each other but different from pancreatic chymotrypsin. BBI has thus distinguished a subpopulation of enzymes capable of hydrolyzing succinyl-Ala-Ala-Pro-Phe-aminomethyl coumarin which may mediate the transformation of C3H/10T1/} cells.