Stability of 11S globulin from Vicia faba seeds

Abstract

Heat denaturation of 11S globulin, a dodecameric globular protein isolated from Vicia faba seeds was studied using scanning microcalorimetry at pH 7.6 and NaCl concentrations from 0 to 1 M. The specific enthalpy of denaturation was shown to be a linear function of temperature. The ratio of the calorimetric enthalpy to the effective one (Van't‐Hoff's) per protomer of 11 S globulin was 0.9 ± 0.06. It is concluded that at first approximation 11 S globulin protomers denaturated independently in conformity with the two‐state model. The plotted temperature‐dependent specific free energy of 11 S globulin denaturation at different NaCl concentrations demonstrated that an increase in the salt content brought about the rise in protein stability. The maximum 11 S globulin stability is reached at about 300°K. The molar free energy of denaturation at 300°K in 1 M NaCl is 918 kJ/mol.