cystine

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cystine:

see cysteinecysteine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of mammalian protein.
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Cystine

 

(also known as β,β’-dithio-di-α-aminopropionic acid), [HOOCCH(NH2)CH2S]2, a sulfur-containing amino acid; a disulfide of cysteine. Cystine exists as two optically active forms— D-cystine and L-cystine—and two optically inactive forms— DL-cystine and wieso-cystine. L-cystine is a component of almost all natural proteins and peptides. Hair and wool keratin contain up to 18 percent cystine (together with cysteine). The covalent disulfide (—S—S—) bonds formed by cystine residues between and within individual polypeptide chains maintain a definite three-dimensional molecular structure for proteins and biologically active peptides. The retention of disulfide bonds is a requisite for the characteristic properties of fibrous proteins, such as keratins, as well as for the normal activity of various hormones, such as oxytocin, vasopressin, and insulin, and for various enzymes, such as ribonuclease and chymotrypsin. Cystine is a non-essential amino acid. Its biosynthesis and metabolism in organisms are closely linked to cysteine, since cystine and cysteine readily interconvert in living organisms.

A hereditary disturbance of cystine metabolism leads to the development in childhood of cystinosis, a disease in which cystine crystals are deposited in the tissues, causing various problems. The increased excretion of cystine in urine—cystinuria—leads in severe cases to the formation of cystine calculi, from which cystine was first isolated in 1810.

E. N. SAFONOVA

cystine

[′si‚stēn]
(biochemistry)
C6H12N2S2 A white, crystalline amino acid formed biosynthetically from cysteine.
References in periodicals archive ?
Scientists realized that the co-administration of L-cystine and L-theanine could restore age-related impairment of immune competence, helping to prevent influenza and other viral infections--and in turn, preventing deadly complications.
The test group received 280 milligrams of L-theanine and 700 milligrams of L-cystine once a day for 14 days.
The scientists found that certain subsets of the L-theanine and L-cystine group had an increased rate of seroconversion, the precise point at which the immune system develops antibody protection against a microorganism as a result of immunization.
The report concluded that, "Co-administration of L-cystine and L-theanine before vaccination may enhance the immune response to influenza vaccine in elderly subjects with low serum total protein or hemoglobin.
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Hertel H, Gollnick H, Matthies C, Baumann I, Orfanos CE: Low dosage retinol and L-cystine combination improve alopecia of the diffuse type following long-term oral administration.
D'Agostini E Fiallo P Penisi TM, Flora S: Chemoprevention of smoke-induced alopecia in mice by oral administration of L-cystine and vitamin B6.