Heterogeneity and Incomplete Disulfide Reduction in the High-sulfur Proteins of Wool

Abstract

During the course of a study into the causes of heterogeneity of the high-sulfur proteins of wool, it was observed that the powerful reducing agent tributylphosphine although able to completely reduce the high-sulfur proteins in 8 M urea at pH 7·5 was unable to do so in the solvent system 5 M sodium iodide-25 % (v/v) propanol. In a preparation prepared in the latter solvent system each electrophoretically resolvable high-sulfur protein was found to contain at least one intrachain disulfide bond and on average there were two of these resistant disulfides to every polypeptide chain, assuming a mean molecular weight of 20000. It is suggested that the high-sulfur proteins take up a particular conformation in 5 M sodium iodide-25 % propanol which makes certain disulfides inaccessible to tributylphosphine. The nature of this conformation is unknown but it may be significant that high-sulfur proteins, normally thought to have no ordered structure, were found by optical rotatory dispersion measurements to contain about 10% ",-helix in 5 M sodium iodide-25 % propanol.