Binding of oxovanadium(V) anion to bovine serum albumin,human serum albumin and bovine pancreatic trypsin

The binding of vanadium(V) to bovine serum albumin (BSA), human serum albumin (HSA), and bovine pancreatic trypsin in the absence and presence of urea has been studied at different pH values and temperatures by spectrophotometric and equilibrium dialysis methods. The binding data were found to be pH and temperature dependent. The binding data at pH 5.57, studied by the absorbance method, were found approximately identical with those obtained from the equilibrium dialysis method at this pH. The enthalpy change at pH 5.57 for vanadium(V)-protein was −368.4 cal Mole⁻¹ for BSA, −328.8 cal Mole⁻¹ for HSA and −1372 cal Mole⁻¹ for trypsin respectively. The association constants and the number of binding sites were calculated from Scatchard plots and found to be at maximum at lower pH and at lower temperature. The free energy of the combining sites was lowest at higher pH and highest at low pH. Therefore, a lower temperature and a lower pH offered more sites in the protein molecule for interaction with vanadium(V) ions. Statistical effects seem to be more significant at lower vanadium(V) ion concentrations, and electrostatic effects more significant at higher concentrations.