Sulfhydryl compounds

The biochemical basis for the toxicity of mercury and mercury compounds results from its ability to form covalent bonds readily with sulfur. Prior to reaction with sulfur, however, the mercury must be metabolized to the divalent cation. When the sulfur is in the form of a sulfhydryl (— SH) group, divalent mercury replaces the hydrogen atom to form mercaptides, X—Hg— SR and Hg(SR)2, where X is an electronegative radical and R is protein (36). Sulfhydryl compounds are called mercaptans because of their ability to capture mercury. Even in low concentrations divalent mercury is capable of inactivating sulfhydryl enzymes and thus causes interference with cellular metaboHsm and function (31—34). Mercury also combines with other ligands of physiological importance such as phosphoryl, carboxyl, amide, and amine groups. It is unclear whether these latter interactions contribute to its toxicity (31,36). 

Seiji, M.T., Yoshida, T., Itakura, H. and Irimajiri, T. (1969). Inhibition of melanin formation by sulfhydryl compounds. J. Invest. Dermatol. 52, 280-286. 

D. (1991). The decrease of superoxide dismutase activity and depletion of sulfhydryl compounds in ethanol-induced liver injury. Drug Alcohol Depend. 28, 291-294. 

Bosma W, Kamminga G, De Kok LJ. 1990. Hydrogen sulfide-induced accumulation of sulfhydryl compounds in leaves of plants under field and laboratory exposure. In Rennenberg H et al., eds. Sulfur nutrition and sulfur assimilation in higher plants Fundamental environmental and agricultural aspects. The Hague, Netherlands SPB Academic Publishing, 173-175. 

De Kok LJ, Thompson CR, Mudd JB, et al. 1983. Effect of hydrogen sulfide fumigation on water-soluble sulfhydryl compounds in shoots of crop plants. Z Pflanzenphysiol Bd 111 85-89. 

Distribution. Lead in blood partitions between plasma and red blood cells, with the larger fraction (90-99%) associated with red blood cells (Cake et al. 1996 DeSilva 1981 Everson and Patterson 1980 Manton and Cook 1984 Ong and Lee 1980a). Lead in plasma binds to albumin and y -globulins (Ong and Lee 1980a). The fraction that is not bound to protein exists largely as complexes with low molecular weight sulfhydryl compounds these may include cysteine, homocysteine, and cysteamine (Al-Modhefer et al. 1991). Approximately 75% was bound to protein when whole human blood was incubated with 50 ig/dL lead (as lead chloride) approximately 90% of the bound lead was associated with albumin (Ong and Lee 1980a). However, the fraction of lead in plasma bound to protein would be expected to vary with the plasma lead concentration. 

Bergstrom et al. [63] used HPLC for determination of penicillamine in body fluids. Proteins were precipitated from plasma and hemolyzed blood with trichloroacetic acid and metaphosphoric acid, respectively, and, after centrifugation, the supernatant solution was injected into the HPLC system via a 20-pL loop valve. Urine samples were directly injected after dilution with 0.4 M citric acid. Two columns (5 cm x 0.41 cm and 30 cm x 0.41 cm) packed with Zipax SCX (30 pm) were used as the guard and analytical columns, respectively. The mobile phase (2.5 mL/min) was deoxygenated 0.03 M citric acid-0.01 M Na2HP04 buffer, and use was made of an electrochemical detector equipped with a three-electrode thin-layer cell. The method was selective and sensitive for mercapto-compounds. Recoveries of penicillamine averaged 101% from plasma and 107% from urine, with coefficients of variation equal to 3.68 and 4.25%, respectively. The limits of detection for penicillamine were 0.5 pm and 3 pm in plasma and in urine, respectively. This method is selective and sensitive for sulfhydryl compounds. 

Ghanayem Bl, Ahmed AE. 1986. Prevention of acrylonitrile-induced gastrointestinal bleeding by sulfhydryl compounds, atropine and cimetidine. Res Commun Chem Pathol Pharmacol 53 141-144. 

Maleic acid imides (maleimides) are derivatives of the reaction of maleic anhydride and ammonia or primary amine compounds. The double bond of a maleimide may undergo an alkylation reaction with a sulfhydryl group to form a stable thioether bond (Chapter 2, Section 2.2). Maleic anhydride may presumably undergo the same reaction with cysteine residues and other sulfhydryl compounds. 

Sulfhydryl Compound Fluorobenzene Derivative Aryl Thioether Bond... 

Although photoreactive aryl azides are relatively inert to thermochemical reactions prior to photolysis, they are not stable in the presence of sulfhydryl compounds which can reduce the... 

The excitation maximum for Br-BODIPY 493/503 is 515nm and its emission occurs at 525 nm when dissolved in methanol. Upon coupling to a sulfhydryl compound, however, the excitation wavelength of the adduct decreases to 493 nm and its emission drops to 503 nm. The very small lOnm Stoke s shift may be a problem, particularly in avoiding interference due to of excitation-light scattering in critical emission measurements. Sub-optimal excitation wavelengths... 

A comparison of the blank corrected values before and after conjugation should give an indication of the percent of peptide coupled. To be more quantitative, a standard curve must be run to focus in on the linear response range of the peptide-Ellman s reaction. Using cysteine as a representative sulfhydryl compound (similar in Ellman s response to a peptide having one free sulfhydryl), it is possible to obtain very accurate determinations of the amount which coupled to the activated carrier. Figure 19.20, discussed previously in this section, shows the results of this type of assay. 

Mead, R.J., D.L. Moulden, and L.E. Twigg. 1985a. Significance of sulfhydryl compounds in the manifestation of fluoroacetate toxicity to the rat, brush-tailed possum, woylie and western grey kangaroo. Austral. Jour. Biol. Sci. 38 139-149. 

HI7. Harpel, P. C., Chang, V. T., and Borth, W., Homocysteine and other sulfhydryl compounds... 

Ross, E. and Schatz, G. Assay of protein in the presence of high concentrations of sulfhydryl compounds. Anal. Biochem. 

Administration of chloroform to laboratory animals resulted in the depletion of renal GSH, indicating that GSH reacts with reactive intermediates, thus reducing the kidney damage otherwise caused by the reaction of these intermediates with tissue MMBs (Hook and Smith 1985 Smith and Hook 1983, 1984 Smith et al. 1984). Similarly, chloroform treatment resulted in the depletion of hepatic GSH and alkylation of MMBs (Docks and Krishna 1976). Other studies demonstrated that sulfhydryl compounds such as L-cysteine (Bailie et al. 1984) and reduced GSH (Kluwe and Hook 1981) may provide protection against nephrotoxicity induced by chloroform. The sulfhydryl compound N-acetylcysteine is an effective antidote for poisoning by acetaminophen, which, like chloroform, depletes GSH and produces toxicity by reactive intermediates. 

In view of the oxidant nature of ozone, a number of investigators have evaluated its effects on intracellular compounds that are normally active in cellular redox reactions. Attention has focused particularly on reduced pyridine nucleotides—reduced nicotinamide adenine dinudeotide (NADH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH)— and on sulfhydryl compounds, specifically reduced glutathione (GSH). 

Chang has made observations on the polysomes of pinto bean leaves exposed to ozone (at 0.35 ppm for 20-50 min). He found that the chloroplast polysomes were more susceptible to oxidation than was the cytoplasmic ribosomes. The sulfhydryl content of the chloroplast ribosomes was also much more susceptible to oxidation than was that of the cytoplasmic ribosomes. Finally, it was found that the effects of ozone on ribosome composition could be reproduced by p-mer-curicbenzoate. Chang s results imply that either ozone itself or a product of ozone oxidation passes from the cytoplasmic membrane to the interior of the chloroplast before having its effect. These results connect with a number of papers on the oxidation of sulfhydryl compounds by ozone. Tomlinson and Rich have reported decreases in leaf sulfhydryl groups after ozone exposure (at 1 ppm for 30-60 min). 

Biochemical Effects Several enzymes that use nicotinamide cofactors were found to ye inhibited by PAN (at 125 ppm for 1 min) in in vitro studies. These enzymes were most susceptible in the absence of substrates. In some cases, an enzyme was protected by the nicotinamide cofactor (e.g., G-6-PD plus NADP), and in other cases, by the cosubstrate (e.g., isocitrate dehydrogenase plus isocitrate). Precisely the same protection could be obtained when compounds that react with sulfhydryl compounds (e.g., p-mercuricbenzoate) were used instead of PAN. Thus, the evidence indicated that PAN reacted with sulfhydryl groups. 

Direct evidence of the reaction of PAN with sulfhydryl compounds has since been obtained (PAN at 115 ppm for 1-10 min). - In the reaction with glutathione, the major products are oxidized glutathione (disulfide) and 5-acetylglutathione. Other sulfhydryl compounds (e.g., coenzyme A, lipoic acid, and cysteine) yield only oxidation products, with no evidence of 5-acetylation. However, acetylation reactions have been observed with alcohols and amines. Sulfur compounds other than thiols can undergo oxidation by PAN methionine is converted to methionine sulfoxide, and oxidized lipoic acid (disulfide) is converted to sulfoxide. 

The second class of biochemicals which is significantly oxidized by ozone is sulfhydryls. The di-sulfhydryl compound, dithiothreitol (DTT), readily loses 2 H to form a cyclic disulfide (26). This compound is used to study how ozone reacts with a sulfhydryl system and whether these reactions are stoichiometric (Fig. 11). 

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