REDUCED-DENATURED RIBONUCLEASE-A IS NOT IN A COMPACT STATE

Dynamic light scattering and circular dichroism experiments were perfo rmed to determine the compactness and residual secondary structure of reduced and by 6 M guanidine hydrochloride denatured ribonuclease A, W e find that reduction of the four disulphide bonds by dithiothreitol a t 20 degrees C leads to total unfolding and that a temperature increas e has no further effect on the dimension, The Stokes' radius of ribonu clease A at 20 degrees C is R(s) = (1.90 +/- 0.04) nm (native) and R(s ) = (3.14 +/- 0.06) nm (reduced-denatured). Furthermore, circular dich roism spectra do not indicate any residual secondary structure. We sug gest that reduced-denatured Ribonuclease A has a random coil-like conf ormation and is not in a compact denatured state.