Denaturation of Tropomyosin by Guanidine Hydrochloride

The denaturation of tropomyosin by guanidine hydrochloride has been studied as a function of denaturant concentration and temperature. Denaturation involves both loss of a helix, which was followed by optical rotatory dispersion, and change in molecular weight. The transition between the native and unfolded states is reversible and the optical rotation results were shown to fulfil some of the criteria for a two‐state process. When the molecule is more than half‐unfolded, subunits of molecular weight 34,000 appear in solution. However the appearance of subunits does not parallel the unfolding as determined by optical rotation, indicating that the whole process cannot be considered as a two‐state one. The molecular weight in the transition region is very dependent on temperature, with indications of a reversible equilibrium between partly unfolded monomer and subunits. The system in this region of guanidine hydrochloride concentration did not show dependence of molecular weight or optical rotation on protein concentration as might be expected for a conformation‐linked association. Guanidine thiocyanate is a more effective denaturant than the chloride for tropomyosin whereas the carbonate and sulphate are relatively ineffective.