Thermochimica Acta, Vol.359, No.2, 181-188, 2000
Thermodynamic parameters for beta-lactoglobulin dissociation over a broad temperature range at pH 2.6 and 7.0
Thermodynamic parameters were determined for the dissociation of beta-lactoglobulin(beta-Lg) at temperatures from -15 to 85 degrees C, The effect of temperature on K-d (equilibrium constant for dimer reversible arrow monomer dissociation) was described by a second-order Van't Hoff equation (ln K-d=AT(-2)+BT-1+C) or Gibbs-Helmholtz equation. The Gibbs free energy (Delta G), enthalpy (Delta H), entropy (Delta S) and thermal capacity (Delta C-p) for beta-Lg dissociation were evaluated. At 25 degrees C standard temperature thermodynamic parameters were Delta G(0)=24.8 (+/-0.35) kJ mol(-1), Delta H-0=57 (+/-13) kJ mol(-1), Delta S-0=92 (+/-30) J mol(-1) K-1 and Delta C-p=2383 J mol(-1) K-1 at pH 2.6. For beta-Lg dissociation at pH 7, Delta G(0)=28.6 (+/-2.7) kJ mol(-1), Delta H-0=107.5 (+/-6.3) kJ mol(-1), Delta S-0=265.7 (+/-39) J mol(-1) K-1 and Delta C-p=2383 J mol(-1) K-1. Simulated temperature-dissociation profiles of beta-Lg show that the fraction of dissociated protein increases with increasing temperature, decreasing pH and with decreasing protein concentration.