Interaction between duodenase, a proteinase with dual specificity, and soybean inhibitors of Bowman-Birk and Kunitz type

The interaction between duodenase, which belongs to a group of Janus-faced proteinases, and classical Bowman--Birk (BBI) and Kunitz (STI) type inhibitors from soybean was investigated. Duodenase was shown to interact only with the antichymotrypsin site (Leu-Ser) of BBI, whereas the antitrypsin site (Lys-Ser) of the inhibitor appeared to be vacant and capable of interaction with trypsin. The inhibition constants of duodenase by BBI, the BBI--trypsin complex, and STI were 4, 400, and 40 nM, respectively.