INTERACTION OF TRYPSIN AND CHYMOTRYPSIN WITH A SOYBEAN PROTEINASE INHIBITOR

The Bowman-Birk inhibitor is an 8,000 molecular weight soybean protein which inhibits tryptic and α-chymotryptic activity. Two distinguishable forms, trypsin-modified and chymotrypsin-modified inhibitor, are produced at acid pH with catalytic amounts of enzyme. The modification caused by chymotrypsin could be the cleavage of a Tyr-X or Phe-X bond without release of a peptide fragment from the inhibitor. In either case, conversion to the modified form is at least 80% complete within 48 hours. Both modified forms are inefficient inhibitors. However, inhibiting capacity comparable to that of native inhibitor is restored upon prolonged exposure at pH 8 to a near-stoichiometric amount of enzyme. After such exposure, both modified forms exhibit native inhibitor characteristics. © 1969.