CIRCULAR DICHROISM STUDIES ON NATIVE FETUIN AND SOME OF ITS DERIVATIVES

Circular dichroism studies on native fetuin suggest that the molecule possesses a low α-helical content in agreement with earlier optical rotatory dispersion studies on this protein. Addition of sodium dodecyl sulfate to the native protein increases the apparent helical content. Neuraminidase-treated fetuin possesses a circular dichroism spectrum similar to the native protein. The disulfide bridges in fetuin stabilize the native structure, since both oxidation and reduction of these moieties at pH 8.0 result in the increased presence of unordered sections in the polypeptide chain. Over the pH range 8.0 to 4.5, the reduced, carboxymethylated and oxidized derivatives all undergo a random coil å β transition. The native protein shows a distinct but complicated fine structure in the 250-300-mμ region, which reflects asymmetrical interactions involving tyrosine, tryptophan and disulfide bridges. When the molecule unfolds on denaturation with 8 M urea, or upon oxidation or reduction of the disulfide bridges, the aromatic side chains are separated from their close association with the centers of optical asymmetry, and the circular dichroism dichroic spectra in this region disappear or are diminished in intensity. © 1969.