Nanomolar concentrations of Bowman-Birk soybean protease inhibitor suppress x-ray-induced transformation in vitro.

Experiments reported here indicate a crude soybean extract, if defatted with acetone, effectively blocks cell transformation in vitro. An active component of this crude extract is the Bowman-Birk trypsin and chymotrypsin inhibitor. The chymotrypsin-inhibitory region of the Bowman-Birk inhibitor is responsible for suppressing in vitro transformation. Another low molecular weight soybean trypsin inhibitor does not significantly suppress transformation. The Bowman-Birk inhibitor (i) has an irreversible effect on the transformation process, (ii) can suppress radiation-induced transformation even when added to cultures many days after the carcinogen exposure, and (iii) is effective in its ability to suppress transformation when present in the medium at a concentration as low as 0.125 nM.