Mercaptoethanol precursors

A range of functional thiols e.g. thioglycolic acid (2) and mercaptoethanol (3)] has been used to produce monofunctional polymers10"54 50 (Section 7.5.2) and thcncc as precursors for diblock copolymers.47... 

Antigen unmasking on sections of paraffin-embedded tissues can be accomplished by reduction of disulfide bonds by treatment with 2-mercaptoethanol, followed by alkylation with sodium iodoacetate to prevent the bonds from reforming. This method has been used for unmasking a Kunitz protease inhibitory domain epitope of Alzheimer s amyloid precursor protein in human brain (Campbell et al., 1999). Sections are reduced with a mixture of 0.14 M 2-mercaptoethanol in 0.5 M Tris-HCl (pH 8.0) and 1 mM EDTA for 3 hr in the dark at room temperature. After being washed for 3 min in distilled water, the sections are treated with a mixture of 250 mg/ml iodoacetic acid in 0.1 M NaOH, diluted 1 10 in 0.5 M Tris-HCl (pH 8.0) and 1 mM EDTA for 20 min in the dark. 

Unlike ethylene glycol, a-hydroxycarboxylic acids, and p-mercaptoethanol, ligands such as ethanolamine, ethylenediamine, amino acids, and 2-aminoethanethiol do not form V2L2 complexes with vanadate [46], However, weakly formed products of VL stoichiometry (—546 ppm, —556 ppm) are observed with a number of a-amino acids [47], Because the amine functionality in amino acids is not suitable for formation of the cyclic [VN]2 core expected for a dimer, then one or the other of these VL compounds may correspond to the monomeric precursor to such a dimeric product. Certainly, with the a-hydroxycarboxylic acids, the monomeric complex can be a major component in solution. Similar VL complexes have not been reported for the amino alcohols. Perusal of the available reports suggests that the amine derivatives were studied under conditions where the nitrogen functionality was protonated, so the results may be somewhat misleading. 

In general, DMS increases during aging (Simpson, 1979 Segurel et al., 2005), instead methyl and ethyl thioacetates hydrolyze, and there is an increase of thiols and disulfides observed (Rauhut, 1996). Another sulfur compound found in wine is bis(2-hydroxyethyl)disulfide, which was found in extracts of wines, in particular from Vitis labrusca grapes or its hybrids (Anocibar Beloqui et al., 1995). This compound is a precursor of H2S and 2-mercaptoethanol, two substances with a very strong rotten egg and unpleasant poultry-like odor, respectively. After... 

Figure 5.3. GC/MS-EI (70 eV) mass spectrum of bis(2-hydroxyethyl)disulfide, a precursor of H2S (strong odor of rotten eggs) and of 2-mercaptoethanol (poultry-like aroma) in wine.

Cinnamic acid (1) is the precursor of -p-coumaric acid (2) in plants, and the presence of enzymes that catalyze the hydroxylation of cinnamic acid to p-coumaric acid has been demonstrated (Butt and Lamb, 1981). These mixed-function oxidases (in peas) are associated with the microsomal fraction and require molecular oxygen, NADPH, and mercaptoethanol for the production of i -p-coumaric acid. p-Coumaric acid has a strong regulatory effect on the en-... 

Cysteine and homocysteine are also important precursors of VSCs, as shown in Figure 17.2. A number of thiols can be generated from cysteine, cysteine conjugate and homocysteine transformation during yeast fermentation, including 2-mercaptoethanol, 3-mercaptoethanol, 3-mercaptohexanol,... 

Fig. 2. Irreversible modification of the polymerase by dADP-ribose. Ten pi portions of 10% washed HeLa cell lysate were incubated with 10 pi of 25 pM [3 P]NAD (63 G/mmol) and 100 pg/ml DNase I. 5 mM 3-aminobenzamide was included in sample (a). After incubation at 37 C for 5 min, 10% TCA was added to samples a and b. Samples c-e were chilled on ice for 5 min, and centrifuged. The pellets were resuspended in lysis buffer (40 mM Tris-Cl (pH 8), 10 mM Mg(O.CO.CH3)2, 5% Dextran, 0.05% Trition X-1(X) and 0.1 mM CaCl2) plus DNase with (c) no nucleotide, (d) 5 mM unlabeled NAD or (e) 5 mM unlabeled dNAD, and were incubated again for 10 min. The incubation was stopped by the addition of TCA. The precipitates were dissolved in 40 pi of gel buffer containing 1% SDS, 1% 2-mercaptoethanol and were analyzed by 7%-15% polyacrylamide gel electrophoresis. Track (c) controls for losses in the wash. The bands labeled in the presence of 3-aminobenzamide are probably the result of non-enzymatic addition of p PJdADP-ribose that was present in the precursor.

In one class of precursors, metal thiolates are formed by adding a thiol (RSH) like 2-mercaptoethanol to a Cd " solution. Previous work [22] has shown that Cd " (but also other metal) ions in the presence of thiols form polynuclear species complexed with RS with the formula [CdCRSsCds) ] . Composition and solubility of the complexes depend not only on metal and thiol concentration but also on pH, as reported previously by Hayes et al. [23] UV-Vis spectra of Cd thiolate complexes exhibit an absorption maximum around 250 nm [23, 24] as shown in Figure 19.3. Upon ultraviolet (254 nm) irradiation, the absorption peak at 250 nm decreased, while a second absorption band in the 270-290 nm appeared. 

Early evidence for long-chain aldehydes as precursors of long-chain alkanes was provided by [ " CJacetate feeding studies of wax biosynthesis in garden peas (Pisum sativum), where p-mercaptoethanol inhibited radiolabel incorporation into alkanes and stimulated radiolabel incorporation into long-chain aldehydes (Buckner and Kolattukudy, 1973). Co-incubation of P. jeffreyi xylem sections with 5 pCi [ " CJacetate and 1 to 50 mM p-mercaptoethanol similarly resulted in inhibition of /7-heptane biosynthesis relative to incubations with [ " CJacetate alone, although radiolabel accumulated into both octanal and 1-octanol in the presence of P-mercaptoethanol. 

Sulfur compounds present in wine can have a detrimental effect on aroma character, producing odors described as garlic, onion and cauliflower, so-called Boeckser aroma. This sulfurous character is correlated with with 2-methyl-3-hydroxythiophene, 2-methyl-3-furanthiol and ethanethiol, and their concentrations in wine are influenced by winery procedures and the use of certain winemaking yeasts (105). Off-flavors in European wines were associated with the nonvolatile bis(2-hydroxyethyl) disulfide, a precursor to the poultry-like character of 2-mercaptoethanol and hydrogen sulfide (106). 

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