MOLECULE

L-Cystine

Cystine is an oxidized dimeric form of cysteine, an amino acid. It is formed by linking two cysteine residues via a disulfide bond (cys-S-S-cys) between the -SH groups. This organosulfur compound has the formula (SCH2CH(NH2) CO2H)2. It is a colorless solid that melts at 247-249 °C. It was discovered in 1810 by William Hyde Wollaston but was not recognized as being derived of proteins until it was isolated from the horn of a cow in 1899. Through formation of disulfide bonds within and between protein molecules, cystine is a significant determinant of the tertiary structure of most proteins. Cystine also functions in redox reactions. Disulfide bonding, along with hydrogen bonding and hydrophobic interactions, is partially responsible for the formation of the gluten matrix in bread. Cystine is found in high concentrations in the cells of the immune system, skeletal and connective tissues, skin, digestive enzymes, and in hair. It is found largely withing nonreducing organelles within cells such as the Golgi, ER, lysosomes and vesicles while cysteine is found in the reducing environment of the cytoplasm and the extracellular space. Cystine is the preferred form of cysteine for the synthesis of glutathione (a tripeptide consisting of cysteine, glutamate and glycine) in cells involved in the immune function including macrophages and astrocytes. Lymphocytes and neurons prefer cysteine for glutathione production. Optimizing glutathione levels in macrophages and astrocytes with cystine allows these cells to provide cysteine to lymphocytes and neurons directly upon demand. Cystine naturally occurs as a deposit in the urine and can form a calculus (hard mineral formation) when deposited in the kidney. Cystine is required for proper vitamin B6 utilization and is also helpful in the healing of burns and wounds, breaking down mucus deposits in illnesses such as bronchitis as well as cystic fibrosis. Cysteine also assists in the supply of insulin to the pancreas, which is needed for the assimilation of sugars and starches. It increases the level of glutathione in the lungs, liver, kidneys and bone marrow, and this may have an anti-aging effect on the body by reducing age-spots etc. Cystine is also found in Cannabis plants (PMID: 6991645).