Keratin contains

Keratins: These are characteristic constituents of chidermal tissue such as horn, hair, nails, wool, hoofs, and feathers. All hard keratins on hydrolysis yield as pa of their amino acids, histidine, lysine, and arginine in the ratio of 1:4:12. The soft or pseudokeratins such as those occurring in the outermost layers of the skin do not have these amino acids in the same ratio. In neurokeratin, the ratio is 1:2:2. Human hair has a higher content of cysteine than that of other species it is called a aa aa-keratin. b bb bb-keratins are deficient in cysteine and, rich in glycine and alanine. They are present in spider&;s web, silk, and reptilian scalesRef: Textbook of medical biochemistry, MN Chatterji, 8th edition, page no: 84