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Binding of the soybean Bowman‐Birk proteinase inhibitor and of its chymotrypsin and trypsin inhibiting fragments to bovine α‐chymotrypsin and bovine β‐trypsin. A thermodynamic study
Author(s) -
Ascenzi Paolo,
Amiconi Gino,
Bolognesi Martino,
Menegatti Enea,
Guarneri Mario
Publication year - 1990
Publication title -
journal of molecular recognition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.401
H-Index - 79
eISSN - 1099-1352
pISSN - 0952-3499
DOI - 10.1002/jmr.300030504
Subject(s) - chymotrypsin , trypsin , chemistry , enzyme , kunitz sti protease inhibitor , binding site , biochemistry , stereochemistry
The effect of pH and temperature on the apparent association equilibrium constant ( K a ) for the binding of the soybean Bowman‐Birk proteinase inhibitor (BBI) and of its chymotrypsin and trypsin inhibiting fragments (F‐C(p), F‐T(p) and F‐T(t), respectively) to bovine α‐chymotrypsin (α‐chymotrypsin) and bovine β‐trypsin (β‐trypsin) has been investigated. On the basis of K a values, the proteinase inhibitor affinity can be arranged as follows: β‐chymotrypsin: BBI ≈ β‐trypsin:BBI ≈ β‐trypsin:F‐T(t) ≈ β‐trypsin:F‐T(p) ≫ α‐chymotrypsin:F‐C(p), F‐C(p), F‐T(p) and F‐T(t) do not inhibit β‐trypsin and α‐chymotrypsin action, respectively. On lowering the pH from 9.5 to 4.5, values of K a for BBI, F‐C(p), F‐T(p) and/or F‐T(t) binding to α‐chymotrypsin and β‐trypsin decrease, thus reflecting the acid‐p K shift of the invariant His57 catalytic residue from 7.0, in the free enzymes, to 5.2, in the proteinase:inhibitor complexes. Considering the known molecular models, the observed binding behaviour of BBI, F‐C(p), F‐T(p) and F‐T(t) was related to the inferred stereochemistry of the proteinase:inhibitor contact regions.