Cystine terms Links

Appendix 4A. We have retained the term cystine to indicate two disulphide-linked cysteines. 

Except for a small amount of the amino acid methionine, the sulfur in wool occurs in the form of the amino acid cystine. Only approximately 82% of clean wool consists of keratinous proteins, which are characterized by a high concentration of cystine. Approximately 17% of the fiber is protein material of relatively low cystine content (<3%) this has been termed nonkeratinous. As a result of the lower cystine content, the nonkeratinous proteins have a lower concentration of disulfide cross-links compared with the keratinous proteins in the fiber. The nonkeratinous material is, therefore, more labile and less resistant to chemical attack than the keratinous proteins. The nonkeratinous proteins are located primarily in the cell membrane complex between the cortical cells and in the endocuticle (Fig. 3). Approximately 13% of the total nonkeratinous material is also located within the cortical cells, where its distribution differs between the cells of the ortho- and paracortex. 

Wool is a protein fiber that is obtained from the fleece of - sheep. Aside from normal domestic sheep, there are other varieties, such as merino. The term w. covers also the hair of lamas (alpaca), camels, rabbits (angora) and goats (mohair, cashmere). Chemically, wool is a - protein, based on keratin, and consists of 24 different - amino acids. Most important is the content of S-containing amino acids (cystine), which are responsible for the disulfide cross-linking. 

---