Op. J. Biophy., Vol. 2 No. 1, 2012, pp. 4-14
Urea denatures proteins at different concentrations, depending on the experimental conditions and the protein. We in- vestigated the pressure-induced denaturation of bovine serum albumin (BSA) in the presence of subdenaturing concen- trations of urea based on a two-state equilibrium. Pressure-induced denaturation was enhanced at urea concentrations of 3.5 M to 8.0 M, with the free energy of denaturation at atmospheric pressure ranging from +5.0 to –2.5 kJ/mol of BSA. The m values appeared to be biphasic, with m1 and m2 of 0.92 and 2.35 kJ mol ·M , respectively. Plots of DG0 versus ln[U] yielded values of the apparent stoichiometric coefficient, of 1.68 and 6.67 mol of urea/mol of BSA for m1 and m2, respectively. These values were compared with the m and stoichiometry values of other monomeric proteins reported in or calculated from the literature. The very low values systematically observed for proteins were suggestive of heterogeneity in the free energy of denaturation. Thus, a stoichiometry value of 140 mol of urea/mol of BSA may indicate the existence of a heterogeneous molecular population with respect to the free energy of denaturation.
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