Keratin is characterised by high content of amino acids such as glycine, alanine, serine and valine. Also, keratin contains in its structure minor amounts of methionine, lysine and tryptophane. Most eminent components (7÷12%) are cystine and cysteine, which are sulphur-containing amino acids. One of the cystine carboxyl groups makes peptide bonds of a single chain, while other groups, i.e. amino and carboxyl, are included in the peptide bond of another polypeptide chain. The chemical activity of keratin is largely dependent on cystine that undergoes hydrolysis, oxidation and reduction. Table 1 presents the amino acids compositionof keratins of different origins.