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

✍ Scribed by Paolo Ascenzi; Gino Amiconi; Martino Bolognesi; Enea Menegatti; Mario Guarneri

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 524 KB
• Volume: 3
• Category: Article
• ISSN: 0952-3499
• DOI: 10.1002/jmr.300030504

✦ Synopsis

Abstract

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.