Revised equilibrium thermodynamic parameters for thermal denaturation of beta-lactoglobulin at pH 2.6

Thermodynamic parameters for thermal denaturation of beta -lactoglobulin (b eta -lg) should account for the dissociation coupled unfolding (DCU) transi tions, Dimer reversible arrow Monomer reversible arrow Unfolded state. Puri fied beta -1g (0.4-4 mg ml(-1) in 50 mM glycine-glycine-HCl buffer, pH 2.6) was heated and monitored by W-difference spectrophotometry. The Monomer re versible arrow Unfolded state transition occurred at 65-95 degreesC with T- m equal to 82 degreesC and a Gibbs free energy change (DeltaG(U)(0)) of 51 kJ mol(-1). Such results were combined with. parameters for beta -1g dissoc iation leading to the Gibbs free energy change for DCU (DeltaG(DCU)(0)) of 128 energy change for DCU (DeltaG(DCU)(0)) of 128 (+/-8.3) kJ mol(-1). The enthalpy and entropy change for DCU was (DeltaH(DCU)(0)) equal to 373 kJ mo l(-1) and (DeltaH(DCU)(0)) 824 J mol(-1) K-1. Thus, the room temperature st ability of beta -1g is 76 kJ mol(-1) higher than reported previously. The p ossible significance of such results for protein stability function relatio ns (PSFR) is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.