The highest concentration of cystine can be found in?

Keratins are a type of intermediate filament that comprises a large poion of many epithelial cells. The characteristics of skin, nails, and hair are all due to keratins. Keratins contain a large amount of the disulfide amino acid cystine. Approximately 14% of the protein composing human hair is cystine. This is the chemical basis of depilatory creams, which are reducing agents that render keratins soluble by breaking the disulfide bridges of these insoluble proteins. The basic structure of intermediate filament proteins is a two- or three-stranded a-helical core 300 amino acids in length. Note: Cystine storage disease: Defective carrier-mediated transpo of cystine results in cystinosis with deposition of cystine crystals in tissues and early moality from acute renal failure. Ref: Rodwell V.W. (2011). Chapter 29. Catabolism of the Carbon Skeletons of Amino Acids. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.