Cystine, properties

Properties and Structure. a -Acid glycoprotein (a -AGP) has a molecular mass of about 41,000 and consists of a peptide chain having 181 amino acid residues and five carbohydrate units (14,15). Two cystine disulfide cross-linkages connect residues 5 and 147 and residues 72 and 164. The carbohydrate units comprise 45% of the molecule and contain siaUc acid, hexosamine, and neutral hexoses. In phosphate buffer the isoelectric point of the... 

Schweitz et al. purified four related toxins (Rpl, RpII, RpIII, and RpIV) from sea anemone Radianthus paumotensis (Rp) and studied their pharmacological properties (9). During the course of initial NMR studies, the reported sequence of RpII was found to have errors, and was redetermined (8). Subsequently Metrione et al. determined the sequence of RpIII as well (10). T e other two Rp toxin sequences are yet to be determined. Sequences of the Rp, and several other sea anemone toxins, are shown in Table I. We have used a two letter code to denote the species consistently and this notation differs from the earlier designations of Norton and Wiithrich groups. In our notation. As la and Ax I correspond to ATX la and AP-A, respectively. From alignment of the cystines in these sequences, it is clear that Rp toxins have three disulfide bonds, as do the other toxins. 

Oxidative bleaching of wool is invariably carried out with hydrogen peroxide. The active species involved is likely to be the same as on cellulosic substrates but specific reactions with wool amino acid residues must be considered. The primary reaction is oxidation of cystine disulphide bonds leading to the formation of cysteic acid residues (Scheme 10.41). The rupture of disulphide crosslinks, with attendant increase in urea-bisulphite and alkali solubility values, adversely affects fibre properties. As the severity of bleaching conditions increases, the urea-bisulphite solubility remains little changed but the relationships between alkali solubility and cysteic acid (Figure 10.36) and between cystine and cysteic acid (Figure... 

A development reported recently [519] involves reduction of the cystine disulphide bonds in wool with either thioglycolic acid or tetrakis(hydroxymethyl)phosphonium chloride to form thiol groups, followed by crosslinking with bifunctional reactive dyes. This gave improved insect resistance but had adverse effects on physical properties such as strength, shrinkage and stiffness, thus limiting the potential of the process for commercial use. 

Investigations of the effects of UV- and hypochlorite-induced oxidative modification of 20 amino acids and human serum albumin (HSA) on their antiradical properties showed unexpected results [36], Seven amino acids (cystine, histidine, methionine, phenylalanine, serine, tryptophan, and tyrosine) and HSA developed ACW following oxidation (see examples in Fig. 14). The fresh (produced in 1998) HSA from Serva had no antiradical capacity, but it acquired this quality during irradiation. The out-of-date HSA sample (Dessau, GDR, 1987, expiration date 7/1/1992) showed a remarkable ACW even in an unirradiated state. 

Fischer and Suzuki soon afterwards showed that Neuberg and Mayer s stone cystine contained tyrosine, and that its different behaviour to protein cystine was due to the presence of this compound. Rothera also could find no difference between stone cystine and protein cystine, and further, Gabriel s synthesis of isocysteine or a-thio-/8-aminopropionic acid and isocystine, which had quite different properties to cystine, though the two were much alike in many of their reactions, proved that stone cystine and protein cystine must be identical substances. Finally, it has been shown by Friedmann that a-thiolactic acid, ammonia PT. I. 4... 

In the case of dibenzoyl cystine the effect of substitution of various groups in the molecule on its properties of gelatinisation supports this hypothesis of growth in dchelon. 

Disulfide bonds in the amino -acid cystine are important to the properties of many proteins by maintaining covalent intramolecular bonds and crosslinks between protein chains (16). 

Advantage is taken of the properties of antimctabolitcs in chemotherapy. In cancer chemotherapy, several antimetabolites are used. These include methotrexate, 6-mercaptopunne, 6-thioguanine, 5-fluorouracil, and cystine arabinoside. In the chemotherapy of metastatic breast cancer, 5-fluorouracil and methotrexate, in combination with cyclophosphamide, have been used. Antimetabolites, sometimes along with corticosteroids, are used in the therapy of various autoimmune diseases, such as thrombocytenic purpura, thyroiditis, Goodpasture s syndrome, among others. 

Y. Liu, K. Breslauer, and S. Anderson, Designing Out Disulfide Bonds Thermodynamic Properties of 30-51 Cystine Substitution Mutants of Bovine Pancreatic Trypsin Inhibitor , Biochemistry, 36, 5323-5335 (1997). 

Notice the R group on each amino acid. The R group is called the side chain of the amino acid. Nearly all organisms use the same 20 a-amino acids to synthesize proteins. Many amino acids and amino acid derivatives, such as hydroxyprotine and cystine, can be created by post-translational modifications after the polypeptide is formed. Ten amino acids are essential. ("Essential" means that they cannot be synthesized by the body, so they must be ingested. Some books list 8 or 9 amino acids as essential. The discrepancy involves whether or not to list as essential those amino acids that are derivatives of other essential amino acids.) Each amino acid differs only in its R group. The R groups have different chemical properties. These proper-... 

Chemically, human hair contains approximately 85 percent protein, 7 percent water, 3 percent lipid, 4.7 percent protein-bound sulfur (as cystine), and low concentrations of trace minerals (e.g., iron, zinc, copper). The phosphorus content is approximately 80 milligrams per 100 grams (0.003 ounces per 3.5 ounces) of hair. Hair is normally associated with sebum and exocrine secretions from skin glands that confer greasiness but influence its water content and mechanical and physical properties. 

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