Cysteic acid, structure

Polydiscamide A (309), discodermins A-H (298-305) and halicylindramides A-E (306-308, 310 and 311) form a series of depsipeptides composed of 13 or 14 amino acids and bear a sulfonic acid group in a cysteic acid residue, with Cys(03H), with the JV-terminus blocked by a formyl group. Their total structures, including absolute stereochemistries, were determined in most cases by a combination of spectral and chemical methods. 

A problem with the chromatographic determination of cysteic acid is that there is almost no retention of cysteic acid. For both reversed-phase HPLC and ion-exchange amino acid analyzers (usually employing cation-exchange resins), cysteic acid is essentially eluted within or near the void volume of the column. This makes it more susceptible to unknown chromatographic interferences from various matrices. When cysteine is alkylated by 3-bromopropylamine, the product (S-3-aminopropylcysteine) looks very similar to lysine in structure. Hale et al. (90) show that this alkylated species affords excellent chromatographic separation on four different commercially available amino acid analysis systems and that, indeed, it does elute very near lysine in each case (see Fig. 4). 

Cystine, which contains a disulfide bond, is reported to be the most numerous and reactive amino acid present in hair keratin. Disulfide bonds in cystine are reduced by mercaptans and phosphines, and oxidized by perborates, bromates, and bleach. These reactions result in structural rearrangements within keratin which may affect the physiochemical properties of hair, since disulfide bonds in cystine contribute to the stability of hair. For example, hydrogen peroxide bleaching of hair is an oxidative process which occurs readily in an alkaline medium. This results in the formation of perhydroxy anions which have been proposed to react with cystine to form cysteic acid residues. The process of bleaching results in the loss of approximately 15% of the cystine bonds originally present in keratin and may explain the increased permeability of bleached hair to chemicals. - ... 

To return now to chain A, Meedom (78) almost completely established the structure of this chain by the classic techniques of partial degradation. The single doubtful detail concerned the relative location of proline and alanine in the fourth and fifth positions. It is now known (67, 75) that aminopeptidase splits cysteic acid and glycine quickly and then valine much more slowly. This fact suggests that proline may be the fourth residue. When the DNP-derivative of the main peptide left behind by amino peptidase is submitted to partial degradation by acid, the dipeptide DNP. -Val.Pro is obtained. Thus the complete sequence may be written ... 

Wang et al. (1994) analyzed by MD the roles of the "double catalytic triad" in papain catalysis, based on the structure of the enzyme, which is not completely known from crystallography (Kamphuis et al., 1984) due to the oxidation state of Cys-25 (present as cysteic acid in the crystal). Stochastic boundary MD (Brooks and Karplus, 1983) was carried out on the whole enzyme + 350 water molecules. Three "layers" were treated according to their distance from the sulfur atom of Cys-25 - atoms within 12A, atoms between 12-16A and the more distant atoms were kept fixed. CHARMM forcefield was employed. The active site geometry was examined as a function of pH, for various mutual states of S-/SH and Im/ImH+. In addition, the mutations of Asp-158 (Menard et al., 1991) were studied. 

It is clear from the results that the structure of wool is extremely complex. Almost all of the monoamino acids occur linked to both sides of glutamic and cysteic acids. The small number of aspartic acid peptides identified is probably due to the lower content of aspartic acid in wool so that the peptide spots would probably be faint and would not show on the chromatograms. 

Unaltered human hair is hair that has not been chemically modified by treatment with bleaches, permanent waves, straighteners, or hair dyes. Numerous publications [6,12-27] describe results of the amino acid analysis of unaltered human hair. Table 2-1 depicts the structures for 21 amino acids that have been identified in human hair. Cysteic acid and other amino acids, derived from those amino acids of Table 2-1, are also present in either weathered or cosmetically altered hair, see Table 2-2. Table 2-3 summarizes results from several sources describing quantitative whole-fiber analyses of these 21 amino acids. These same amino acids are classified according to functional group in Table 2-4. 

Probably the most important achievement in insulin research was the determination of its primary structure by Frederick Sanger and his associates in Cambridge, England. In order to elucidate the amino acid sequence of the hormone it was necessary to separate the two chains constituting the molecule. This was accomplished by oxidation with performic acid. This operation cleaved the three disulfide bridges by converting each cystine to two cysteic acid residues ... 

Investigations into urine and plasma samples must consider that certain compounds such as antibiotics are not metabolized after its administration. Antibiotics pass through the body without changing their structure and, finally, get into the urine or plasma and interfere with the amino acid analysis via reaction with ninhydrin. Perry et al. [52] reported this problem for the first time. In urine samples oxidized with hydrogen peroxide, they detected a signal in the retention range of cysteic acid and homocystine, which they attributed to o-penicillamine-sulfonic acid. This compound was formed by oxidation of the antibiotic D-peni-cillamine, which was administered to the patient whose urine was investigated. 

An alternate and competing pathway for the metabolism of cysteinesulfinic acid is its oxidation to cysteic acid (reaction 7, Fig. 2). A new enzyme, L-cysteinesulfinate dehydrogenase, has been isolated from P. vulgaris which catalyzes this reaction. Its unique property is that it is reported to require a hitherto unknown coenzyme, designated as Co III, for activity. A good source of Co III is boiled yeast extract. The reduced form of the coenzyme has an absorption spectrum characteristic of dehydropyridine nucleotides. The structure of this supposed new coenzyme is uncertain. The fact that it can substitute for DPN in many reactions supposedly specific for the latter leads to some wonderment. 

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