Cystine Content of Wool

Abstract

Disulfide bonds in wool were reduced with tri-n-butylphosphine in 50% n-propanol at pH 7.6. Native and generated sulfhydryl groups were then alkylated in the same medium with 2-vinylpyridine. Cystine and the original of cysteine residues were thus changed quantitatively to residues of S-β-(2-pyridylethyl)-L-cysteine (2-PEC). Occurrence of this new amino acid in hydrolyzates of the modified wool was confirmed by independent synthesis. 2-PEC is stable to acid hydrolysis and is eluted from the basic physiological column of an amino acid analyzer as a discrete peak before arginine. Quantitative modification of sulfhydryl groups in reduced keratins to 2-PEC permits quantitative determination of cysteine or of cystine via cysteine by two independent techniques-ion-exchange chromatography and ultraviolet spectroscopy. The new procedure is suitable for routine analyses.