Description

L-cystine (formula: (SCH2CH(NH2) CO2H)2), the L-form of cystine) is a covalently linked dimeric nonessential amino acid formed through the oxidation of cysteine. It is contained in many foods including eggs, meat, dairy products, and whole grains as well as in skin and hairs. L-cystine and L-methionine are the amino-acids required for wound healing and formation of epithelial tissue. It is able to stimulate the hematopoietic system and promote the formation of white and red blood cells. It can also be used as a component of parental and enteral nutrition. It can also be used for the treatment of dermatitis and protection of liver function. L-cystine is manufactured through the enzymatic conversion from DL-amino thiazoline carboxylic acid.

Chemical Properties

A white or almost white, crystalline powder, practically insoluble in water and in alcohol.

Uses

L-Cystine is a non-essential amino acid for human development. L-Cystine is formed by the dimerization of two cysteines through the sulfur.

General Description

This Standard Reference Material (SRM) is intended primarily for use in validating microchemical procedures for the determination of carbon, hydrogen, nitrogen, and sulfur in organic matter. SRM 143d is pure crystalline cystine supplied in a 2 g unit size. For more information, please refer to the SDS and COA.SRM 143D_cert SRM 143D _SDS

Biochem/physiol Actions

Cysteine is the source of disulfide linkages in proteins and has a role in sulfur transport. It undergoes rapid oxidation to form cystine at physiological pH. L-cystine is crucial for oxygen production and low density lipoprotein modification by arterial smooth muscle cells. It also has a role in the synthesis of glutathione.

Safety Profile

Low toxicity by ingestion. When heated to decomposition it emits toxic fumes of PO, and SOx

Purification Methods

Cystine disulfoxide impurity is removed by treating an aqueous suspension with H2S. The cystine is filtered off, washed with distilled water and dried at 100o under a vacuum over P2O5. Crystallise it by dissolving in 1.5M HCl, then adjusting to neutral pH with ammonia. Likely impurities are D-cystine, meso-cystine and tyrosine. Also purify it by dissolving it in 10% NH3 and adding gradually dilute AcOH until the point of precipitation and cooling slowly [Dughton & Harrison Acta Cryst 12 396, 402 1959.] Alternatively dissolve it in 6N NH4OH and evaporate it at room temperature for crystallisation to occur. [Chaney & Steinrauf Acta Cryst 30 711 1974, Beilstein 4 IV 3155.]