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-lacto globulin(beta-Lg) at temperatures from -15 to 85 degrees C, The effect of t emperature on K-d (equilibrium constant for dimer reversible arrow monomer dissociation) was described by a second-order Van't Hoff equation (ln K-d=A T(-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=26 5.7 (+/-39) J mol(-1) K-1 and Delta C-p=2383 J mol(-1) K-1. Simulated tempe rature-dissociation profiles of beta-Lg show that the fraction of dissociat ed protein increases with increasing temperature, decreasing pH and with de creasing protein concentration. (C) 2000 Elsevier Science B.V. All rights r eserved.