Circular dichroism of denatured barstar suggests residual structure,.

The circular dichroism (CD) spectrum of the denatured state of barstar has been analyzed as a function of urea and temperature. The near- and far-UV CD spectra change very rapidly in magnitude and shape with increasing temperature, unlike those of native protein, suggesting the presence of residual structure that changes with denaturing conditions. The effect of mutations indicates that there is residual structure in helix1 of the protein, consistent with NMR data. The changes in CD with conditions are consistent with the denatured state being a mixture of conformations of similar energy.