The dimer of cysteine produced when its sulphydryl group (—SH) is oxidised forming a disulphide ( S—S—) bridge.
Two cysteine amino acids that are covalently linked via a disulfide bond. These units are important in biochemistry in that disulfide bridges represent one important way in which the conformation of a protein is maintained in the active form. Cystine bridges lock the structure of the proteins in which they occur in place by disallowing certain types of (molecule) chain movement. When the disulfide bond is with a “free” cysteine (i.e., one that is not a part of the same protein molecule’s amino-acid backbone) the “free” cysteine is known as a thiol group. Cystine can be metabolized from methionine by certain animals (e.g., swine), but not vice versa.
A sulfur-containing, nonessential amino acid that occurs notably in keratin and insulin. In the diet, exerts a sparing effect on methionine.
An amino acid. It can cause stones to form in the urinary system of people who have a rare inherited metabolic disorder.
A molecule containing two cysteines joined through the terminal sulfur atoms.
Cystine is an amino acid produced as a metabolite of cysteine. Although cystine is not incorporated into proteins within the body, it is formed within proteins by the joining of two cysteine thiol side-chains in the production of a disulfide bond. Disulfide bonds are important in determining a protein’s conformation and providing stability to the structure.
A sulfur-containing amino acid produced by the action of acids on proteins that contain this compound. It is an important source of sulfur in metabolism.
Under normal circumstances, the kidney tubules are responsible for reabsorbing an amino acid. However, in the case of cystinuria, an inherited disorder, the body fails to reabsorb cystine and certain other amino acids in sufficient quantities. Consequently, cystine crystals precipitate within the kidneys, leading to the development of obstructive renal failure.