Dynamic light scattering and circular dichroism experiments were performed to determine the compactness and residual secondary structure of reduced and by 6 M guanidine hydrochloride denatured ribonuclease A. We find that reduction of the four disulphide bonds by dithiothreitol at 20°C leads to total unfolding and that a temperature increase has no further effect on the dimension. The Stokes' radius of ribonuclease A at 20°C is R s = (1.90 ± 0.04) nm (native) and R s = (3.14 ± 0.06) nm (reduced-denatured). Furthermore, circular dichroism spectra do not indicate any residual secondary structure. We suggest that reduced-denatured Ribonuclease A has a random coil-like conformation and is not in a compact denatured state.
