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 ?
The levels of essential amino acids except cystine and methionine were comparable with that for the FAO reference protein.
Nephropathic cystinosis comprises 95% of cystinosis, a rare, life-threatening metabolic lysosomal storage disorder that causes toxic accumulation of cystine in all cells, tissues, and organs in the body.
We collected 4 urine fractions from each of the participating patients and detected 15 fractions with cystine supersaturation (42% of all investigated collection fractions).
Urinary cystine excretion and capacity in patients with cystinuria.
Renal crystal deposits and histopathology in patients with cystine stones.
Struvite, or infection stones take place with kidney or urinary tract infections while cystine stones make up less than 1% of kidney stones.
Cystine stones make up less than one percent of kidney stones and are more likely to develop in families with an inherited condition that leads to an excess of the chemical cystine in the urine.
Finally, Martin-Venegas also demonstrated that metabolism of HMTBA was more diverted to trans-sulfuration pathway, forming more Cystine and Taurine, strong detoxifying and anti-oxidant molecules.
It is caused by a build up of the amino acid cystine in her cells.
c) Breast Milk (a) Amino Acid Cheese WPC (c) Acid WPC (b) (ESPGHAN) Cystine 30 37 38 Histidine 44 46 41 Isoleucine 115 103 92 Leucine 192 207 169 Lysine 164 176 114 Methionine 46 48 24 Phenylalanine 78 80 81 Threonine 117 90 77 Tryptophan 32 36 33 Tyrosine 76 80 75 Valine 123 106 99 Met + Cys 76 85 62 Phe + Tyr 154 160 156 (a) ESPGHAN formulae recommendations Phenylalanine (Phe) + Tyrosine (Tyr) may be added together if the Phe:Tyr ratio is (0.
1 mL inoculated into 10mL) and mannitol selenite cystine (MSC) broth (Oxoid CM 399) (1 nat.
Kaiser-Kupfer devoted much of her research and clinical work was nephropathic cystinosis, a rare disease in which cystine crystals build up in the cornea.