(redirected from Cysteinyl)
Also found in: Dictionary, Thesaurus, Medical.


(sĭs`tēn), organic compound, one of the 20 amino acidsamino acid
, any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins.
..... Click the link for more information.
 commonly found in animal proteinsprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
..... Click the link for more information.
. Only the l-stereoisomer participates in the biosynthesis of mammalian protein. It is particularly abundant in the proteins of hair, hooves, and the keratinkeratin
, any one of a class of fibrous protein molecules that serve as structural units for various living tissues. The keratins are the major protein components of hair, wool, nails, horn, hoofs, and the quills of feathers.
..... Click the link for more information.
 of the skin. Cysteine's importance is related to the presence of a sulfur-containing thiol group in its side chain. This group participates in the catalytic reactions of certain enzymes, such as that of papain, the enzyme from papaya latex used to make commercial meat tenderizers. The thiol group of one cysteine residue is capable of combining with the thiol group of another to form a disulfide bridge, either linking two peptide chains together, as in the case of insulininsulin,
hormone secreted by the β cells of the islets of Langerhans, specific groups of cells in the pancreas. Insufficiency of insulin in the body results in diabetes. Insulin was one of the first products to be manufactured using genetic engineering.
..... Click the link for more information.
, or causing a single peptide chain to fold back on itself, making a loop. This latter effect on the secondary structure of proteins is evidently of great importance in maintaining the proper configuration of both structural proteins and enzymes. Two cysteine molecules linked together by a disulfide linkage make up the amino acid cystine, often occurring as a separate entry in lists of common amino acids. A major complication of cystinuria, an inherited metabolic disease, one of whose symptoms is a twentyfold to thirtyfold increase in urinary excretion of cystine, is the precipitation of this relatively insoluble amino acid in the kidney, impairing its function. A similar sort of renal failure often accompanies cystinosis, another inherited disease. Cystine was isolated from a urinary calculus in 1810 and from horn tissue in 1899. The reduction of cystine to cysteine was reported in 1884, and the structures of the two amino acids were proved by chemical synthesis in 1903–4. Neither cysteine nor cystine is essential to the diet of man; cystine and cysteine are interconvertible, and cysteine is made in the body from serineserine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
..... Click the link for more information.
 and methioninemethionine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the L-stereoisomer appears in mammalian protein. It is one of the several essential amino acids needed in the diet; the human body cannot synthesize it from simpler metabolites.
..... Click the link for more information.



(also known as α-amino-β-thiopropionic acid), HSCH2CH(NH2)COOH, a sulfur-containing amino acid. Cysteine occurs in the optically active L- and D- forms as well as the racemic DL- form. L-cysteine is a component of glutathione and almost all natural proteins.

In the hydrolysis of proteins, cystine is converted into cystine, from which cysteine may be obtained by reduction. Cysteine is a replaceable amino acid. In mammals it is synthesized from the amino acids methionine and serine with the participation of adenosine triphosphate (ATP); in the process, cystathionine is formed as an intermediate. In some microorganisms and plants, cysteine is formed from serine and hydrogen sulfide with the participation of acetyl-coenzyme A and is used in the synthesis of methionine.

Because of the high reactivity of the sulfhydryl (—SH) groups, cysteine plays an important role in metabolism. The sulfhydryl groups of cysteine radicals at the active center of thiol enzymes either establish the enzyme-cofactor bond or participate directly in the enzymatic reaction—that is, in the formation and decomposition of the enzyme-substrate complex. Cysteine radicals located outside the active center give the enzyme its catalytically active conformation.

Cysteine plays a protective role in the body by binding toxic heavy metal ions (with the formation of mercaptides), arsenic compounds, cyanides (with the formation of thiazolidines), and aromatic hydrocarbons (with the formation of mercapturic acid). Cysteine and its decarboxylation product, cystamine, are used as radioprotectors. Cysteine is also used for the treatment of cataracts in early stages.


Young, L., and G. Maw. Metabolizm soedinenii sery. Moscow, 1961. (Translated from English.)
Meister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)
Torchinskii, Iu. M. Sul’fgidril’nye i disul’fidnye gruppy belkov. Moscow, 1971.



C3H7O2NS A crystalline amino acid occurring as a constituent of glutathione and cystine.
References in periodicals archive ?
These mayblockthe undesirable side effects ofboth [LTB.sub.4] and [LTC.sub.4] (a cysteinyl derived leukotriene) [89].
A study was carried out by Singh et al., in 2005, which showed that Zileuton, 5-LOX inhibitor and cysteinyl LT receptor antagonists, montelukast, Zafirlukast inhibited the number of writhes in acetic acid-induced writhing method but did not show analgesic activity in tail flick and hot plate methods.
Another limitation is the lack of biological surrogate markers like cysteinyl leukotriene levels which have shown to be higher in acute asthma exacerbations.
Severity of atherosclerotic lesions and plaque instability correlate with 5-LO levels [9], with both LT[B.sub.4] and the cysteinyl LTs involved in atherosclerosis development [10].
Cysteinyl leukotrienes such as LTC4, LTD4, and LTE4 are well-known mediators for inflammatory response and are involved in acute and chronic inflammatory conditions such as asthma and glomerulonephritis, and DPEP has an important role in elimination of leukotrienes by conversion of LTD4 to LTE4 [71].
Caspases (cysteinyl aspartate-specific protease) are the key regulatory enzymes of the apoptotic cascades [41].
These include the major granule-derived mediators histamine and tryptase and newly synthesised cysteinyl leukotrienes, whose effects on ASM contractility are well established.
The cell wall contains many phosphates, carbonyl and cysteinyl ligands which maintain the integrity of the membrane by acting as a diffusion barrier.
In addition to natural inhibitors some synthetic inhibitors like endopin 2C modified as serpinendopin 2C show selective inhibition of cathepsin L compared to papain or elastase [26]; other inhibitors like peptidyl-diazomethyl ketones are also useful irreversible inhibitors for inactivating cysteinyl proteinases in vitro and in vivo more effectively against cathepsin L than cathepsin S [27].
Quinones react nonenzymatically with nucleophilic moieties lysyl, tyrosyl, cysteinyl, and histidinyl residues of proteins [143-145].
Effects of a cysteinyl leukotriene receptor antagonist on eosinophil recruitment in experimental allergic rhinitis.