PLANT SERINE PROTEINASE-INHIBITORS - STRUCTURE AND BIOCHEMICAL APPLICATIONS ON PLASMA KALLIKREIN AND RELATED ENZYMES

The action of two Bowman-Birk and several plant Kunitz-type inhibitors were studied on trypsin, chymotrypsin, plasma kallikrein and factor X II. The primary structure of some of them was completely defined. The results showed that the Bowman-Birk type inhibitors, although potent i nhibitors for trypsin (K-i in the range of 1-2 nM), are not able to in hibit plasma kallikrein, Factor XII (K-i = 1.4 mu M) and chymotrypsin (K-i = 5.0 nM) are inhibited by Torresea cearensis trypsin inhibitor ( TcTI) but not by Dioclea glabra trypsin inhibitor (DgTI). Both inhibit ors reactive site regions are highly homologous, and the amino acid re sidues in P1 position are the same, Lys and His; major differences are in the charge of the C-terminal portion of the molecules, The studied Kunitz-type inhibitors were all able to inhibit plasma kallikrein (Ki between 4 and 80 nM), with the exception of Schizolobium parahyba chy motrypsin inhibitor (SpCI), that is specific for chymotrypsin. All Kun itz-type inhibitors inactivate chymotrypsin, but with a dissociation c onstant in the range of 0.1 to 0.6 mu M Factor XIIf is inhibited with K-i in the range of 0.1 mu M. Bauhinia bauhinioides trypsin inhibitor (BbTI) did not promote factor XIIf inhibition. The Kunitz-type inhibit ors are a highly homologous, sharing 60% identity in the N-terminal po rtion of the loop containing the reactive site, and 28.6% identity in the C-terminal portion of the same loop.