Cysteic acid from cysteine

Cysteic acid (3-sulfoalanine, l-amino-3-sulfopropionic acid) [13100-82-8, 3024-83-7] M 169.2, m 260"(dec). Likely impurities are cystine and oxides of cysteine. Crystd from water by adding 2 volumes of EtOH. When recrystd from aqueous MeOH it has m 264-266°, and the anhydrous acid has m 260°(dec). [Chapeville and Formageot Biochim Biophys Acta 26 538 1957 J Biol Chem 72 435 1927.]... 

Sanchez-Cano et al. have proposed paired synthesis for obtaining L-cysteic acid and L-cysteine from L-cystine which greatly improves the economical parameters [57], The global process-flow for the paired synthesis, with L-cystine and water as starting materials is shown in Fig. 3. Table 2 compares the results for the paired (B) and the individual syntheses (A, C). 

Fig. 24-25), another component of nervous tissue. Cysteic acid can arise in an alternative way from O-acetylserine and sulfite (reaction 1, Fig. 24-25), and taurine can also be formed by decarboxylation of cysteine sulfinic acid to hypotaurine and oxidation of the latter (reaction m). Cysteic acid can be converted to the sulfolipid of chloroplasts (p. 387 Eq. 20-12). 

The two preparations from A. oryzae reportedly differ in amino acid and carbohydrate composition. The enzyme prepared by Minato contained 25% carbohydrate no cysteine was detected either by titration with p-mercuribenzoate in 6M urea or by cysteic acid analysis after performic acid oxidation (179). In contrast, Wolfenden et al. (92) reported 14 cysteine residues per mole of enzyme which reacted instantaneously with p-mercuribenzoate in the absence of urea. No explanation is available for this apparent discrepancy. 

More recently, there have been numerous collaborative studies (81-84) that have attempted to improve the accuracy and precision of this method. A typical example by MacDonald et al. (81) reported a collaborative study by seven laboratories. Samples were oxidized with performic acid for 16 hours over ice bath. After oxidation, HBr was used to destroy excess performic acid. Samples were then roto-evaporated to dryness, dissolved in 6N HC1, nitrogen purged, and then hydrolysed for 18 hours at 100°C. Interlaboratory precision for cysteic acid determination in six food ingredients ranged from 7 to 10%. For methionine sulfone, interlaboratory precisions ranged from 1 to 13% for the same six food ingredients. The mean recovery of cysteine was 95% and of... 

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). 

Cysteic acid is obtained in nearly quantitative yield from cysteine with aqueous hydrogen peroxide in the presence of iron(II) ions.397 Molybdates and tungstates have also been used as effective catalysts for similar transformations.398 An excellent route for the oxidation of 2-thioethanol to isothionic acid has been developed.399 Heteropolyoxometallates supported on alumina400 can also be used to oxidize a range of organo-sulfur compounds. For example, alkyl monosulfides to sulfoxides and sulfones, and thiols to sulfonic acids are a few possibilities (Figure 3.98). 

Figure 14.7. Pathways for the synthesis of taurine from cysteine. Cysteine sulfinate decarboxylase, EC 4.1.1.29 cysteic acid decarboxylase, EC 4.1.1.29 (glutamate decarboxylase, EC 4.1.1.15) cysteine oxidase, EC 1.13.11.20 cysteamine oxygenase, EC 1.13.11.19 and hypotaurine oxidase, EC 1.8.1.3. Relative molecular masses (Mr) cysteine, 121.2 cysteamine, 77.2 cysteine sulfinic acid, 153.2 cysteic acid, 169.2 hypotaurine, 109.1 and taurine, 125.1.

Synthesis of 1-cysteic acid and 1-cysteine from cystine RSSR —> RSO3H ... 

These 3 sulfur-containing amino acids and their derivatives are susceptible to oxidation and other destructive reactions. Even when great care has been taken to remove all oxygen from hydrolysis tubes, considerable losses of cysteine and cystine are found after acid hydrolysis, and this usually prevents direct quantitation of these amino acids in proteins. However, total cysteine plus half-cystine content may be determined as cysteic acid after performic acid... 

The protein is completely hydrolyzed by acid (6 N HCl, 24 hours or longer at 110°C, under vacuum or inert gas) to its constituent amino acids and the resultant hydrolysate is evaporated to dryness. The amino acid composition is determined on protein hydrolysates obtained after 24,48, and 72 hours of acid treatment. The content of amino acids with bulky aliphatic side chains such as isoleucine, leucine, and valine, which undergo slow hydrolysis, is calculated from an extrapolation of the hydrolysate data to infinite time. The content of hydroxyl-containing amino acids, which are slowly destroyed during hydrolysis, is obtained by a corresponding extrapolation to zero time. Since cysteine, cystine, and methionine residues are somewhat unstable to hydrolysis, these residues are oxidized to cysteic acid and methionine sulfone, respectively, with performic acid before quantitative analysis. Cysteine, or half-cystine, is quantitated as a derivative such as carboxymethyl cysteine after reduction and alkylation, a necessary prerequisite to subsequent sequence analysis. Tryptophan... 

The in vivo mechanism of 35S-taurine formation from 35S-cysteine in the rat has been studied by Awapara and Wingo148. Ten minutes after injection, large amounts of 35S cysteine and traces of sulphate-35S were found only in the liver. After 20 minutes small amounts of 2-aminoethanesulphinic-3 5 S acid were also found (equation 81). Taurine began to appear in the liver 30 minutes after the injection. Two hours after administration, analyses for [35S]taurine, alanine, [35S]cysteic acid and 2-aminoethanesulphinic acid were carried out in liver, kidney, heart and spleen of the rats. [3 5S]Cysteic acid had been detected only when large amounts of 35S-labelled cysteine were injected. It has been suggested that the degradation of [35S]cysteine in vivo proceeds in rats according to equation 81. Formation of 2-aminoethanesulphinic acid and its oxidation to taurine is a preferred pathway. Much less [35S]sulphate than 2-aminoethanesulphinic-35S acid and taurine-35S had been found one hour after incorporation of 35S-labelled cysteine. 

Enzymatic decarboxylation169 of L-cysteic acid-35S (equation 86) by the tissues of chicken embryo has been investigated by Fromageot and coworkers170. Enzyme preparations from liver appeared to be the most active, and the authors determined [35S]taurine as well as unreacted 35S-cysteic acid, 35S-/Lsulphonylpyruvic acid and 35S-sulphate. The reaction is inhibited by L-cysteine sulphinic acid, by DL-a-methylcysteic acid, CH2ICOONa, NaCN and by hydroxylamine. The enzyme is activated by pyridoxal phosphate. 

The metabolism of 35S-labelled sulphur amino acids in marine and fresh water invertebrates has been studied and reviewed by Awapara and coworkers179 180. The general conclusion drawn from these studies was that the metabolism of sulphur-bearing amino acids in two molluscs studied is qualitatively the same as in mammals. Taurine, which serves as an osmoregulator in marine molluscs, is formed either by decarboxylation of cysteic acid (in Rangia cuneata) or by oxidation of hypotaurine (in Mytilus edulis), derived from cysteinesulphinic acid by decarboxylation. In Arenicola cristata only the terminal reactions are different. Methionine and cysteine sulphur incorporates into taurocyamine by transamidation between taurine and arginine. 

The amino acid composition of either the whole HDL or each of the subclasses has been found identical and different from the low-density lipoprotein class (Shore, 1957 Scanu and Hughes, 1962). Particularly high contents of glutamic acid and leucine were found as contrasted with a low content of methionine (Shore, 1957 Scanu and Hughes, 1962). Cysteine or cystine as cysteic acid was either absent (Scanu and Hughes, 1962) or present in small amounts (V. Shore and B. Shore, 1962). 

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