Thermodynamic analysis of interactions between denaturants and protein surface exposed on unfolding: Interpretation of urea and guanidinium chloride m‐values and their correlation with changes in accessible surface area (ASA) using preferential interaction coefficients and the local‐bulk domain mode

A denaturant m‐value is the magnitude of the slope of a typically linear plot of the unfolding free energy change ΔG°obs vs. molar concentration (C3) of denaturant. For a given protein, the guanidinium chloride (GuHCl) m‐value is approximately twice as large as the urea m‐value. Myers et al. (Protein Sci 1995;4:2138–2148) found that experimental m‐values for protein unfolding in both urea and GuHCl are proportional to ΔASA  corrmax , the calculated maximum amount of protein surface exposed to water in unfolding, corrected empirically for the effects of disulfide crosslinks: (urea m‐value/ΔASA  corrmax ) = 0.14±0.01 cal M−1 Å−2 and (GuHCl m‐value/ΔASA  corrmax ) = 0.28±0.03 cal M−1 Å−2.

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