Microcalorimetric study on conformational change of denatured RNase A adsorbed onto a moderately hydrophobic surface

The microcalorimetric method was used to measure the displacement adsorption heat of denatured (by 1.8 mol L−1 guanidine hydrochloride (GuHCl)) Ribonuclease A (RNase A) adsorbed onto a moderately hydrophobic surface (PEG-600) from various ammonium sulfate ((NH4)2SO4) concentration solutions at 298 K. According to the thermodynamics of the stoichiometric displacement theory for adsorption (SDT-A) and the measured adsorption isotherms, the adsorption thermodynamic functions, ΔG, ΔS, ΔH, and their fractions were obtained. In combination with FTIR analysis, the regulation of conformational change of adsorbed denatured RNase A was found. The results showed that the moderately hydrophobic surface can provide energy to denatured protein and make it gain more ordered conformation with (NH4)2SO4 concentration increment. The analysis of thermodynamic fractions showed that the contribution of four subprocesses associated with the displacement adsorption of RNase A was different in various (NH4)2SO4 concentrations.