Kinetic and thermodynamic analysis of leech-derived tryptase inhibitor interaction with bovine tryptase and bovine trypsin

The interaction of leech-derived tryptase inhibitor (LDTI) with bovine live r capsule tryptase (BLCT) and bovine trypsin has been studied using both th ermodynamic and kinetic approaches. Several differences were detected: (i) the equilibrium affinity of LDTI for BLCT (K-a = 8.9 x 10(5) M-1) is about 600-fold lower than that for bovine trypsin (K-a = 5.1 x 10(8) M-1); (ii) L DTI behaves as a purely non-competitive inhibitor of BLCT, while it is a pu rely competitive inhibitor of bovine trypsin. These functional data are com pared with those previously reported for the LDTI binding to human tryptase , where tight inhibition occurs at two of the four active sites of the tetr amer (K-a = 7.1 x 10(8) M-1). Amino acid sequence alignment of BLCT, human beta II-tryptase and bovine trypsin allows us to infer some possible struct ural basis for the observed functional differences.