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 ?
Nephropathic or "classic infantile" cystinosis the most common and most severe form of the disease is typically diagnosed in infancy and requires lifelong cystine depleting therapy.
Whereas, lipase, cystine arylamidase and napthol-AS-BI-phosphohydrolase were found at low grade level-2 (Fig.
Some of the promoters include cell membrane lipids (phospholipids, cholesterol, and glycolipids) [42], calcitriol hormone enhancement via parathyroid hormone stimulation [101], oxalate, calcium, sodium, cystine, and low urine volume [34].
We found statistically significant correlations between increased resistance to 5-fluorocytosine and higher enzymatic activity of alkaline phosphatase, chymotrypsin, and alpha-glucosidase; increased resistance to fluconazole and higher enzymatic activity of esterase and beta-glucosidase as well as increased susceptibility to ketoconazole and higher enzymatic activity of cystine arylamidase; increased susceptibility to fluconazole and higher enzymatic activity of mannosidase.
Although the topical cysteamine therapy had not reduced the opacities in the cornea caused by cystine crystals, no ocular or systemic complications were observed.
The average mean HU was reported as 565-698 HU for cystine and 700-1438 HU for CaOX stones in different studies (5,6,7,8).
Analysis of 24-hour urine will show elevated cystine concentrations of greater than 400 mg/L urine (Biyani & Cartledge, 2006).
The results for disulphides, S-sulfonate, cystine monoxide, and carboxylates are displayed in Figure 2 and data for cystine dioxide and cysteic acid are shown in Figure 3.
Plasma fHcy, tHcy, methionine (Met), and cystine (Cys) are monitored and tHcy and fHcy levels are lowered to within the recommended therapeutic range by dietary restriction of natural protein/methionine.
Immunocal has previously been shown to substantially increase blood or lymphocyte GSH levels in patients with HIV infection or cystic fibrosis, respectively, owing to its high concentration of nondenatured whey proteins containing the cysteine precursor, cystine (see Table 1 for composition) [30-32].
Crodasone Cystine and Keravis are included in the Step 1 formulation to build bonds and strengthen hair.
Pharmaceutical scientists in Sunderland have been awarded PS150,000 by the Cystinosis Foundation (CF) UK to support their research, which they hope will help them transform treatment for cystinosis, a devastating illness which occurs when the body becomes unable to process cystine, an amino acid.