title: Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to human Lys77-plasmin.
abstract: The effect of pH and temperature on the association equilibrium constant (Ka) for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI Kunitz inhibitor) to human Lys77-plasmin has been investigated. Ka values decrease with decreasing pH, reflecting the acid-pK and -midpoint shifts, upon BPTI binding, of a single ionizable group, between pH 5 and 9, and of a three-proton transition, between pH 3 and 5. At pH 8.0, values of thermodynamic parameters for BPTI binding to human Lys77-plasmin are: Ka = 1.2 X 10(9) M-1, delta G degree = -12.2 kcal/mol, and delta S degree = +49 entropy units (at 21 degrees C); and delta H degree = +2.3 kcal/mol (temperature independent between 5 degrees C and 45 degrees C; 1 kcal = 4184 J). BPTI binding properties of human Lys77-plasmin have been analysed in parallel with those of serine (pro)enzymes acting on cationic and non-cationic substrates. Considering the known molecular structures of homologous serine (pro)enzymes, or Kunitz and Kazal-type inhibitors and of their complexes, the observed binding behaviour of BPTI to human Lys77-plasmin was related to the inferred stereochemistry of the enzyme-inhibitor contact region.
mesh_terms: D000818:Animals; D007611:Aprotinin / Q000378:metabolism*; D001665:Binding Sites; D002417:Cattle; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010446:Peptide Fragments / Q000378:metabolism*; D013696:Temperature
chemical_list: D010446:Peptide Fragments; C033809:lys-plasmin; D007611:Aprotinin; D005341:Fibrinolysin