Disulfide containing proteins denatured in 6 mol/L guanidinium chloride are not completely unfolded

The unfolded states of serum albumin, lysozyme and ribonuclease denatured in GuHCl with their disulfide bridges intact or reduced and carboxyamidomethylated have been compared by their circular dichroism, second-derivative and difference spectra in the ultraviolet region. Results obtained indicate that although the secondary structures of denatured proteins with intact disulfides are largely destroyed, they still have considerable ordered conformation even in 6 mol/L guanidinium chloride as indicated by the differences in the extents of exposure of the aromatic residues compared to the denatured proteins without the native disulfide bonds.