DSC studies of the conformational stability of barstar wild‐type

The temperature induced unfolding of barstar wild‐type of bacillus amyloliquefaciens (90 residues) has been characterized by differential scanning microcalorimetry. The process has been found to be reversible in the pH range from 6.4 to 8.3 in the absence of oxygen. It has been clearly shown by a ratio of δH_vH/δH_cal near 1 that denaturation follows a two‐state mechanism. For comparison, the C82A mutant was also studied. This mutant exhibits similar reversibility, but has a slightly lower transition temperature. The transition enthalpy of barstar wt (303 kJ mol⁻¹) exceeds that of the C82A mutant (276 kJ mol⁻¹) by approximately 10%. The heat capacity changes show a similar difference, δC_p being 5.3 + 1 kJ mol⁻¹ K⁻¹ for the wild‐type and 3.6 δ 1 kJ mol⁻¹ K⁻¹ for the C82A mutant. The extrapolated stability parameters at 25 °C are δG° = 23.5 + 2 kJ mol⁻¹ for barstar wt and δG⁰ = 25.5 + 2 kJ mol⁻¹ for the C82A mutant.