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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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(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.



C6H12N2S2 A white, crystalline amino acid formed biosynthetically from cysteine.
References in periodicals archive ?
44 (BE2) g kg-1 feed DM from October to December, at relatively stable cystine levels, had a beneficial influence on growth performance, protein digestibility and nitrogen retention in blue Arctic foxes.
We found statistically significant correlations between increased resistance to itraconazole and higher enzymatic activity of naphthyl phosphohydrolase and alpha-galactosidase; increased resistance to fluconazole and higher enzymatic activity of trypsin and beta-glucosidase; increased susceptibility to 5-fluorocytosine and higher enzymatic activity of alkaline phosphatase, valine arylamidase, trypsin and chymotrypsin; increased susceptibility to ketoconazole and higher enzymatic activity of cystine arylamidase.
Impairment of the transporter system responsible for transporting cystine out of lysosomes results in the accumulation of cystine crystals in tissues such as the kidneys, eyes, bone marrow, liver, spleen, pancreas, thyroid, skeletal muscles, thyroid, and brain.
The goal of treatment in cystinuria is to prevent recurrence of stones by decreasing urinary cystine concentrations to below the solubility limit (< 250 mg/L) or increasing the solubility of cystine.
Stark, On the reversible reaction of cyanate with sulfhydryl groups and the determination of NH2-terminal cysteine and cystine in proteins, J.
Quantification of intracellular cystine is critical to both diagnosis and therapeutic monitoring of cystinosis patients.
The effect of amino acids like, alanine, aspartic acid, cysteine, cystine, glutamine, histidine, lysine, tyrosine, thiamine, leucine and lysine supplemented in the basal medium was investigated.
The abovementioned data suggest that old fibroblasts may be deficient in cystine transport.
Struvite (magnesium ammonium phosphate) and calcium oxalate calculi are the most common canine uroliths, followed by urate, silicate, cystine and mixed types.
URS is a treatment alternative in cases where shock wave lithotripsy failed in patients with impacted or cystine stones, obese patients, individuals with bleeding diathesis, pregnant women and in centres without ESWL facility.
Eggs from laying hens, 32 and 44 weeks old, were distributed in a totally randomized experimental design within a 3 x 2 x 2 x 2 factorial scheme, covering the following factors: RCP--reduction of crude protein and methionine + cystine (control, valorization of one and two times the protease enzyme); PRO protease (with or without); STO--storing conditions (at room temperature or under refrigeration); TM--stocking period (14 and 28 days), with a total of 24 treatments, with seven replications of one egg per experimental unit.
Its resistance stems from the synthesis of the toxic defense protein, Maize Insect Resistant Cystine Protease 1 (Mir1-CP).