Cyst ine

Schieberle, P. and Hofmann, T. 1998. Characterization of key odorants in dry-heated cyste-ine/carbohydrate mixtures-comparison with aqueous reaction systems. In Flavor Analysis. (C.J. Mussinan and J. Morello, eds.) American Chemical Society, Washington, D.C. 

Other catabolic products include sulfenic acids (R-SOH), S-glucuronides, S-methylconjugates, cyste-ine-S-conjugates, and more. 

Olney, J.W., Misra, C.H. and DeGubareff, T. (1975). Cyste-ine-5-sulfate a brain damaging metabolite in sulfite oxidase deficiency. 7. Neuropathol. Exp. Neurol. 34 167-176. 

Kirley, T.L. (1989) Reduction and fluorescent labeling of cyst(e)ine-containing proteins for subsequent structural analysis. Anal. Biochem. 180, 231-236. 

The problems encountered are numerous. Tryptophan is highly prone to degradation in acid digestions. This is especially the case in food analysis, where samples often contain significant quantities of carbohydrates that greatly exacerbate tryptophan s degradative tendencies. Cyst(e)ine is partially oxidized during acid hydrolysis and will likely be found in several forms cystine, cysteine, cysteine sulfinic acid, and cysteic acid. Methionine can be partially lost in simi-... 

In addition to their importance as essential amino acids for humans, the quantitative determination of cysteine and methionine seems to be growing in importance in the animal feed industry. The dietary requirements for the sulfur amino acids tend to be very high in many animals. This is presumably due to the magnitude of hair/feather growth and the fact that the structural proteins that comprise hair/feathers often have high cyst(e)ine content. 

The analysis of methionine and cysteine is problematic. The sulfur containing side chains of these amino acids are prone to oxidation. The standard hydrochloric acid hydrolysis will cause the partial conversion of these amino acids into cystine, cysteine, cysteine sulfinic acid, cysteic acid, methionine, methionine sulfoxide, and methionine sulfone. The classic strategy (79) for dealing with this problem is simply to drive the oxidative process to completion (i.e., convert all the cyst(e)ine to cysteic acid) and then to analyze chromatographically for cysteic acid and/or methionine sulfone. This is traditionally accomplished by a prehydrolysis treatment of the sample with performic acid. While this method has sufficed over the years, the typical recovery (85 -90%) and precision (4% intra- and 15% interlaboratory) have been poor (80). 

It has been presumed that there are two possible causes for the poor recoveries of cyst(e)ine as cysteic acid. The first is the incomplete conversion of cyst(e)ine to cysteic acid by the per-formic acid oxidation. The second is the oxidative destruction of cysteic acid during the HC1 digestion due primarily to the presence of residual performic acid at elevated temperatures. In response to this possibility, many studies have employed the addition of HBr after the oxidative pretreatment to consume excess/residual peroxide. An interesting collaborative study reported by Llames and Fontaine (84) compares the use of HBr vs. metabisulfite for the purpose of scavenging leftover peroxide. It appears the use of hydrobromic acid yields slightly better results. 

Fruits and vegetables Cls with ion pairing, EC detection of native cyst(e)ine 229... 

AA Toran, R Barbera, R Farre, MJ Lagarda, JC Lopez. HPLC Method for cyst(e)ine and methionine in infant formulas. J Food Sci 61 1132-1135, 1996. 

BJ Mills, CT Stinson, MC Liu, CA Lang. Glutathione and cyst(e)ine profiles of vegetables using high performance liquid chromatography with dual electrochemical detection. J Food Comp Anal 10 90-101, 1997. 

Siliaed, R., Joenvall, H., Caelquist, M., Mutt, V. (1993). Chemical assay for cyst(e)ine-rich peptides detects a novel intestinal peptide ZF-1, homologous to a single zinc-finger motif. Ear. J. Biochem. 211, 377-380. 

E. Cho, N. Johnson and B. Snider, Tissue Glutathione as a Cyst(e)ine Reservoir During Cystine Depletion in Growing Rats, J Nutrition 114 (1984) 1853-1862. 

Ookhtens M, Kaplowitz N (1998) Role of the liver in interorgan homeostasis of glutathione and cyst(e)ine. Semin Liver Dis 18 313-29... 

Cystalysin bas a relatively broad substrate specificity. In addition to L-cysteine, cystalysin accommodates /3-cbloroalanine, cysteine metbyl ester, S -etbylcysteine, and xS-metbylcysteine as substrates for /3-elimination reactions. " In addition cystalysin exhibits a bigb catalytic versatility. It is a cyst(e)ine C—S lyase, catalyzes AlaR reaction, tbe /3-desullination of L-cysteine sulfmic acid and tbe /3-decarboxylation of L-aspartate and oxalacetate. a,/3-Elimination and racemization probably share the step leading to the quinonoid intermediate, and the same catalytic residues. ... 

Carbon atom 5 of the penicillins [as (198)] has been shown to derive from C-3 of cyst(e)ine [as (201)]. In feeding experiments with (2R, 3R)-[2,3- H2]cysteine, 2R, 3S)-[3- H]cysteine, and [3,3 - H2]cystine the fates of the hydrogen atoms originally present at C-3 of cysteine have been examined. As expected tritium label was to some extent lost from C-2 of cysteine. More importantly, retention of nearly one half of the tritium from [3,3 - H2]cystine indicated that hydrogen loss from C-3 was stereospecific. Further, high retention of tritium at C-5 of the penicillin G (199) derived from (2R, 3l )-[2,3- H2]cysteine and low retention in the experiment with (2R, 3S)-[3- H]cysteine demonstrates that it is the 3-pro-S hydrogen of cysteine which is lost in penicillin biosynthesis, and overall the transformation occurs with retention of configuration, as it does for valine. 

Hart and Filner (1969) reported that sulfate uptake by cultured tobacco cells was strongly inhibited by L-cyst(e)ine and L-homocyst(e)ine. L-Methionine and GSH were less inhibitory. Smith (1975) confirmed that... 

Several of the protein amino acids are however degraded by pathways unique to higher plants, e.g., methionine, cyst(e)ine, tryptophan. 

Cyst(e)ine occurs in biological tissues and fluids, both in the free sulfhydryl form, cysteine, and in the disulfide form, cystine In the methods of sample preparation described above, cysteine is oxidized to cystine, and the proportion of the two forms in a sample cannot be determined. A method was devised to accomplish this, involving immediate addition to the sample of iodoacetate, which rapidly reacts with cysteine, converting it quantitatively to the stable S-carboxymethyl derivative (Brigham et al., 1960). Cystine is unaffected by iodoacetate. Both cystine and S-carboxymethylcysteine can be quantified by amino acid analysis. This same strategy can be used with other sulfhydryl compounds, such as homocyst(e)ine. 

Beer contains 150-400 ppm of sulphate (Table 22.2). The major non-volatile organic sulphur compounds in wort are the amino acids cyst(e)ine and methionine and the peptides and proteins which contain them. Some of these compounds will survive into beer. In addition malt contains 5-methyI-methionine and dimethyl sulphoxide which are precursors of dimethyl sulphide. Hops may be a source of sulphur they are often dusted with elemental sulphur or sprayed with dithiocarbamate insecticides. In addition sulphur is usually burnt in the oast. The sulphur compounds present in hop oil are discussed in Chapter 13. 

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