Comparative inhibition of trypsins from several species by soybean trypsin inhibitors

Inhibition by soybean trypsin inhibitor (SBTI) preparations of trypsins and of total proteolytic activity from several species was compared. Rat, monkey, human, bovine, porcine and mink trypsins were all inhibited 90-100% by SBTI, although there were species differences at low SBTI concentrations. Extent of inhibition of trypsin from the various species did not correlate with SBTI-induced pancreatic enlargement. Total proteolytic activity was inhibited up to 40% in rat, monkey, and human preparations by SBTI, and inhibition curves were similar. SBTIs extracted from unheated soy protein isolate (USPI) or raw soy flour (RSF) were approximately equal in their ability to inhibit human trypsin. SBTI extracted from heated soy protein isolate (SPI) was slightly less effective in inhibiting human trypsin than SBTI from either RSF or USPI.