Reactive sites of an anticarcinogenic Bowman-Birk proteinase inhibitor are similar to other trypsin inhibitors.

The three-dimensional structure of the Bowman-Birk type proteinase inhibitor (PI-11) has been deter; mined by x-ray crystallography and refined at 2.6-A resolution.This protein is a specific inhibitor of trypsin.Two reactive site loops, one at each end of the PI-I1 molecule, are structurally similar to each other and to reactive-site loops of pancreatic secretory trypsin inhibitor (Bolognesi, M.,