Cysteine sulfinic acid

However, Phinney (8) has suggested on the basis of experiments with mutants of Neurospora that the biosynthesis of cysteine involves the coupling of sulfate with an organic compound (presumably cysteine sulfinic acid) followed by reduction to sulfide. He noted also that sulfate may be reduced stepwise to sulfide and may then enter the protein as such. But he observed this process proceeds less readily than when sulfate combines first with protein. 

HO g Ss C02H 0 NH2 Occurs in mammalian tissues Cysteine sulfinic acid - intermediate in the biosynthesis of taurine (taurine is essential for many biological processes) 13... 

A quantitatively important pathway of cysteine catabolism in animals is oxidation to cysteine sulfinate (Fig. 24-25, reaction z),450 a two-step hydroxyl-ation requiring 02, NADPH or NADH, and Fe2+. Cysteine sulfinic acid can be further oxidized to cyste-ic acid (cysteine sulfonate),454 which can be decarbox-ylated to taurine. The latter is a component of bile salts (Fig. 22-16) and is one of the most abundant free amino acids in human tissues 455-457 Its concentration is high in excitable tissues, and it may be a neurotransmitter (Chapter 30). Taurine may have a special function in retinal photoreceptor cells. It is an essential dietary amino acid for cats, who may die of heart failure in its absence,458 and under some conditions for humans.459 In many marine invertebrates, teleosts, and amphibians taurine serves as a regulator of osmotic pressure, its concentration decreasing in fresh water and increasing in salt water. A similar role has been suggested for taurine in mammalian hearts. A chronically low concentration of Na+ leads to increased taurine.460 Taurine can be reduced to isethionic acid... 

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). 

Another route of metabolism for cysteine sulfinic acid is transamination to 3-sulfinylpyruvate, a compound that undergoes ready loss of S02 in a reaction analogous to the decarboxylation of oxaloacetate (reaction o, Fig. 24-25). This probably represents one of the major routes by which sulfur is removed from organic compounds in the animal body. However, before being excreted the sulfite must be oxidized to sulfate by the Mo-containing sulfite oxidase. The essentiality of sulfite oxidase is evidenced by the severe neurological defect observed in its absence (Chapter 16). 

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-... 

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). 

Chang TS, Jeong W, Woo HA, Lee SM, Park S, Rhee SG. 2004. Characterization of mammalian sulfiredoxin and its reactivation of hyperoxidized peroxiredoxin through reduction of cysteine sulfinic acid in the active site to cysteine. J Biol Chem 279 50994-51001. 

Biological oxidation of cysteine can yield, in addition to the disulfide cystine, cysteine sulfinic acid and the sulfonic acid cysteic acid. 

Male Sprague Dawley rats, seven days post weanling (Bantin and Kingman, Inc., Fremont, CA) were fed pelleted rodent chow (5001, Ralston Purina Co., St. Louis, MO) or modified AIN-76 diets (BioServ, Inc., Frenchtown, NJ) with or without added sulfur amino acids. Chow, diets, and water were supplied to the rats ad libitum. The AIN-76 diet (16) was modified to contain 12% casein (normally 20% casein), and the weight difference made up with cornstarch. The normal methionine supplement was not included. The cornstarch and sucrose portions were held separately from the casein/vitamin/mineral (CVM) mixture for the purpose of mixing amino acids with the cornstarch and sucrose (CsS). Methionine (MET), methionine sulfoxide (MSO) and cysteine sulfinic acid (CSA) were obtained from Sigma Chemical Co., St. Louis, MO. Cysteine monoxide (CMO) was prepared by the method of Savige et al., (17). 

Cyphomandra invertase inhibitor 13.8U Cypress camphor 5.7Gt Cystatins 13.5Bn Cysteic acid 3.3Ao, 5.5Bo Cysteine 3.3Ao, 14.2o Cysteine sulfinic acid 3.3Ao, 5.5Bo Cytisine 3.1Aa, 3. IBa Cytism scoparius lectin 12.2A Cytisus sessifolius lectin 12.2A Cytochalasin B 9.6A Cytochalasins A-M 9.6A... 

A combination of D-amino acid oxidase and L-amino transferase is an example of a deracemization by stereoinversion. The product is an L-amino acid. The reaction catalyzed by amino transferase has an equilibrium constant close to unity, a very unpractical situation leading to uncomplete transformation and to the production of almost inseparable mixtures of amino acids (at least two, the amino acid product and the amino add used as an amino donor). For preparative purposes it is therefore mandatory to shift the equihbrium to the product side. A recent example of a deracemization procedure based on this coupled enzymatic system is the preparation of L-2-naphthyl-alanine 6 as illustrated in Scheme 13.9 [28]. The reaction occurs in one pot with initial oxidation of the D-amino acid catalyzed by D-amino acid oxidase from Rhodotonda gracilis. The hydrogen peroxide that is formed in stoichiometric amounts is decomposed by catalase. The a-keto add is the substrate for L-aspartate amino transferase (L-Asp amino transferase), which is able to use L-cysteine sulfinic acid 7 as an amino donor. 

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.

Oxidation to cysteic acid, followed by decarboxylation to taurine. Cysteic acid and cysteine sulfinic acid decarboxylase activities occur in constant ratio in various tissues, and it is likely that both substrates are decarboxy-lated by the same enzyme. In general, cysteine sulfinic acid is the preferred substrate, and there is little formation of taurine by way of cysteic acid. 

In the liver and brain, the main pathway is by way of cysteine sulfinic acid, whereas in tissues with low cysteine sulfinic acid decarboxylase activity the main precursor of taurine is cysteamine. 

The central nervous system has at least three enzymes capable of decar-hoxylating cysteine sulfonic acid, one of which is glutamate decarboxylase. Glutamate and cysteine sulfinic acid are mumaUy competitive. In some brain regions, more than half the total cysteine sulfinic acid decarboxylase activity may be from glutamate decarboxylase. 

Taurine is a dietary essential in the cat, which is an obligate carnivore with a limited capacity for taurine synthesis from cysteine. On a taurine-free diet, neither supplementary methionine nor cysteine will maintain normal plasma concentrations of taurine, because cats have an alternative pathway of cysteine metabolism reaction with mevalonic acid to yield felinine (3-hydroxy-1,1-dimethylpropyl-cysteine), which is excreted in the urine. The activity of cysteine sulfinic acid decarboxylase in cat liver is very low. 

It is not known to what extent taurine may be a dietary essential for human beings. There is little cysteine sulfinic acid decarboxylase activity in the human liver and, like the cat, loading doses of methionine and cysteine do not result in any significant increase in plasma taurine. This may be because cysteine sulfinic acid can also undergo transamination to /3-sulfhydryl pyruvate, which then loses sulfur dioxide nonenzymically to form pyruvate, thus regulating the amount of taurine that is formed from cysteine. There is no evidence of the development of any taurine deficiency disease under normal conditions. 

Canet-AvUes RM, Wilson MA, Miller DW, Ahmad R, McLendon C, Bandyopadhyay S, Baptista MJ, Ringe D, Petsko GA, Cookson MR (2004) The Parkinson s disease protein DJ-1 is neuro-protective due to cysteine-sulfinic acid-driven mitochondrial localization. Proc Natl Acad Sci US A 101 9103-9108... 

Oxidation to cysteine sulfinic acid, followed by decarboxylation to hypo-taurine tmd oxidation to taurine. In most tissues, it is the decarboxylation... 

The two cysteines that are bound trans to the peptide ligands have been found (by X-ray crystallography) to be modified by oxygenation to cysteine-sulfenic acid (Cys-SOH (34)) and cysteine-sulfinic acid (Cys-S02H (35)) derivatives. ... 

It is apparent that methodological problems limit the usefulness of the kinetic approach to studying mechanisms. However, data of an entirely different nature argue against a sequential model for the aspartate transporter. Studies of the metabolism of cysteine sulfinic acid show that it is transported by the glutamate/aspartate transporter and that it transaminates with a-ketoglutarate or oxalacetate to yield glutamate or aspartate and jS-sulfinyl pyruvate, which spontaneously hydrolyzes into sulfite and pyruvate [148,149]. 

When mitochondria are loaded with glutamate, cysteine sulfinic acid exchanges with glutamate, and efflux of protons can be observed. No proton movements are observed in conjunction with the cysteine sulfinic acid/aspartate exchange. Therefore, cysteine sulfinic acid must be transported electrogenically as the anion. 

FIGURE 2.40 The major pathway for taurine biosynthesis in the liver- First, cy teine is converted to cysteine sulfinic acid in an oxygen-requiring reaction catalyzed by an iron metalloeozyme- The second step, catalyzed by a vitamin B -requiring enzyme, is a decarboxylation reaction. The final step appears to be catalyzed by a copper metaLloenzyme and to require oxygen. Apparently, about one-fourth of the cysteine in the liver eventually is converted to taurine. 

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