Sulfur-containing compounds glutathione

It is of note that alkaline and acid phosphatase exhibit no silikatase activity. Divalent sulfur-containing compounds, such as sulfide, methionine, cysteine and glutathione have a positive effect on silica uptake536) also water temperature and silica concentration in the aqueous phase control the Si-cycle in cellular systems529-531, 53 ). 

Sulfur-containing compounds have been shown in vitro to interact with tributyltin compounds to produce other compounds with lower hemolytic activity (Byington et al. 1974). It has also been shown in vitro that the toxic properties of dibutyltin dichloride may be enhanced by meso, 2-3,-dimercapto-succinic acid, by means of a hydrophobic reaction with glutathione enzymes (Henninghausen and Merkord 1985). Such interactions could be of importance in treatment of organotin poisonings. 

N-Acetyl-L-cysteine (NAC) is a natural sulfur-containing compound that is produced in living organisms from the amino acid cysteine. It is involved in the intracellular synthesis of a chemical called glutathione (or GSH). Cells (particularly liver cells)... 

Sulfur-containing compounds such as alpha-lipoic acid, methylsulfonylmethane, glutathione, N-acetylcysteine and cysteine are effective against oxidative stress and cell damage caused by free radicals (Bray and Taylor 1993, Pollack et al. 1996). Alpha-lipoic acid increases the antioxidant potency of further antioxidants such as vitamins E and C (Kagan et al. 1992). The course of acute pancreatitis is dramatically impaired in cases of very low antioxidant status. Whereas the sulfur antagonist selenium reduced remarkably the death rate (Kulinski et al. 1995), methionine was also used successfully in the treatment of this disease (Uden et al. 1990). 

In the nonprotein fraction reduced glutathione, GSH, is ubiquitous, and is commonly a mqjor constituent (Table I). The soluble fraction of plants also includes a variety of other sulfur-containing compounds that are normally present in relatively small amounts (a) Intermediates on the route to protein cysteine and protein methionine, such as cysteine, cystathionine, homocysteine, and methionine, (b) Compounds involved in methyl transfer reactions and polyamine synthesis AdoMet.t AdoHcy, and, presumably, 5 -methyl-thioadenosine. The biochemistry of the compounds in both groups (a) and (b) will be discussed here, (c) Compounds clearly related metabolically to cysteine or methionine, such as 5-methylcysteine and 5-methylmethionine. Because in certain plants these derivatives comprise a major portion of the nonprotein sulfur amino acids, they will be discussed here, (d) A number of compounds of uncertain function, the biochemistry of which has often not been clarified. Discussion of such compounds (Richmond, 1973 Fowden, 1964) is beyond the scope of this chapter. 

D.L. Rabenstein and R. Saetre, Mercury-based electrochemical detector for liquid chromatography for the detection of glutathione and other sulfur-containing compounds. Anal Chem., 1977, 49, 1036-1039. 

It is of interest to note that the thiol form of TPP contains the j3-thiol-ethylamine configuration present in coenzyme A. The fact that glutathione, coenzyme A, and the pyruvate oxidation factor all are sulfur-containing compounds is highly suggestive of the possibility that TPP is also active in the thiol form. Cavallini has recently shown that in vitro at pH 7.4, the oxidation of GSH by oxygen in the presence of traces of copper or cytochrome c may be coupled with a simultaneous oxidation of pyruvate to acetate and CO2. The reaction probably depends on the intermediate formation of a GSH-pyruvate complex and is suggested as a possible model for the action of TPP. 

Recently, it was first reported that, with a BDD electrode, four important sulfur-containing compounds, including two biologically important amino acids (homocysteine and glutathione (GSH)), one vitamin (2-mercapto ethanesulfonic acid) and one antibiotic (cephalexin) can be determined by cyclic voltammetry. Their structures are shown in Fig. 15.1. 

The fatty acid-like leukotrienes derived from the addition of glutathione to products of the lipoxygenase branch of the arachidonic cascade are closely associated with manifestations of asthma. Many compounds designed to antagonize leukotrienes at the receptor level incorporate long alkyl chains to mimic the leukotrienes backbone in addition to the sulfur-containing moieties that stand in for glutathione. The reaction... 

The reaction of sulfur-containing biomolecules with platinum antitumor compounds, thereby preventing binding to the critical DNA target, is a possible mechanism of inactivation and is supported by numerous studies. Thus, glutathione (GSH, a cysteine-containing tripeptide see also Fig. 6), which is the predominant intracellular thiol and is present in concentrations varying from 0.5 to 10 mM, is able to inhibit the reaction of DNA with [Pt(en)Cl2] (74) and with cis-Pt (75, 76). It has also been observed that the presence of cysteine can inhibit the reaction between cis-Pt and d-Guo (77). Furthermore, the antitumor activity of cis-Pt was proved to be inhibited by coadministered methionine (78, 79) and even a bis-adduct between cis-Pt and methionine has been isolated from the urine of patients (80). 

A possible function of this intracellular sulfur cycle is to buffer, i.e. to homeostatically regulate, the cysteine concentration of the cells. Irrespective of whether sulfate, cysteine, or sulfur dioxide is available as sulfur source, the intracellular sulfur cycle would allow a plant cell to use as much of these compounds as necessary for growth and development. At the same time, it would give a plant cell the possibility to maintain the cysteine pool at an appropriate concentration by emitting excess sulfur into the atmosphere. Thus, emission of hydrogen sulfide may take place when the influx of sulfur in the form of sulfate, cysteine, or sulfur dioxide exceeds the conversion of these sulfur sources into protein, glutathione, methionine, and other sulfur-containing components of the cell. 

Selenium is an essential trace element and an integral component of heme oxidase. It appears to augment the antioxidant action of vitamin E to protect membrane lipids from oxidation. The exact mechanism of this interaction is not known however, selenium compounds are found in the selenium analogs of the sulfur-containing amino acids, such as cysteine and methionine. Se-cysteine is found in the active sites of the enzyme glutathione peroxidase, which acts to use glutathione to reduce organic hydroperoxides. 

Measuring the total concentration of urinary thio compounds (including glutathione conjugates, mercapturic acids, and other sulfur-containing carbon disulfide metabolites) can serve as a good marker of exposure. The level of total thio compounds correlates with carbon disulfide exposure levels and is a more sensitive biomarker of exposure than the iodine-azide test (Beauchamp et al. 1983 Van Doom et al. 

In addition to the sulfur-containing amino acids methionine and cysteine, inorganic sulfate, sulfur dioxide and organic sulfur compounds such glutathione, taurine and N-acetyl-methionine (to a lesser extent) are also important for the sulfur intake by sparing the required amounts of methionine and cysteine in the diet. The natural content of sulfur dioxide of food is far lower than the total sulfur content (Table 5.4). Sulfur dioxide is used for food conservation, and this in turn has led to the proposal of upper limit values for this sulfur compound (see Section 5.7 and Table 5.11). 

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