Biologically Important Thiols

Spectrophotometric Complex formation with metals (e.g. ferric ions) Colorimetric reaction e.g. nitroprusside reaction) 

Electrochemical Differential pulse polarography Cathodic stripping voltammetry 

Chromatographic Cation-exchange with post-column detection e.g. amino acid analysis) 

HPLC Post-column derivatisation e.g. Ellman s reagent) Non-specific pre-column derivatisation e.g. of amino acids to form chromophores or fluorophores) Pre-column derivatisation to form fluorophores e.g. with bimanes, maleimides) Oxidative and reductive electrochemical detection 

Capillary Electrophoresis Direction detection at low wavelengths Derivatisation followed by appropriate detection 

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Winterbourn CC, Metodiewa D (1999) Reactivity of biologically important thiol compounds with superoxide and hydrogen peroxide. Free Rad Biol Med 27 322-328 Yu X-Y, Barker JR (2003a) Hydrogen peroxide photolysis in acidic solutions containing chloride ions. 

E. Jelleum, V. A. Bacon, and W. Patton, W., Quantitative determination of biologically important thiols and disulfides by gas-liquid chromatography, Anal. Biochem. 31, 339-347, (1969). 

Thiol groups enter some biologically important thiol compounds by the direct incorporation of cysteine itself. Most frequently this involves peptide bond formation. The incorporation of cysteine into proteins does not differ from any other amino acid involving activation as an amino acid adenylate, transfer to a specific transfer ribonucleic acid (t-RNA), and assembly by ribosomal enzymes as coded by messenger ribonucleic acid (m-RNA). It should be pointed out that cystine, the two-headed ... 

Shpigun, L. K., M. A. Suranova, N. A. Ryabova et al. 2010. Voltammetric determination of biologically important thiols in pharmaceutical preparations. 11th Eurasia Com/, on Chem. Sci., Jordan. 

The N-G/CoPc/GC electrode was evaluated toward the electrooxidation of biologically important thiols (u-cysteine, L-glutathione, and 2-mercaptoethane sulfonic acid). A synergic effect between the N-G and CoPc was observed, with a significant enhancement on the electrocatalytic activity of the modified electrode toward thiols oxidation, which can be attributed to the efficiency of the faster electron transfer between the modified electrode surface and the substrates. 

In addition, nonenzymatic acylation of cysteine thiols on proteins incubated in the presence of acyl-CoA has been described, although the biological importance of this process is still unclear. 

The conversion (19) of thiols to disulphides coupled with reduction of flavin (vitamin B2 family) is a topic of import in connection with coenzyme reactivity in flavoenzymes. Since flavin oxidation of thiols involves nucleophilic attack of thiolate ion in the rate-determining step (Loechler and Hollocher, 1975 Yokoe and Bruice, 1975), this biologically important reaction would be markedly affected by hydrophobic environments. 

Dioxetanes are readily reduced to 1,2-diols (Scheme 30) by lithium aluminum hydride (75CJC1103), thiols (88AG(E)429), and biologically important reductants (89MI 133-02) such as ascorbic acid, tocopherol, dihydronicotinamide adenine dinucleotide (NADH), and riboflavin adenosine diphosphate (FADH2). 

An early example of DSR employed dynamic thiolester systems, generated from transthiolesterification reactions, combined with hydrolases in aqueous solution [2, 3]. The transthiolesterification reaction, of fundamental biological importance [4], is the reversible reaction between a thiolester and a thiol. This dynamic reaction is rapid and sufficiently stable under mild conditions in aqueous solution. Dynamic thiolester systems could thus efficiently be generated from a series of thiolester compounds and thiols. During equilibration, the hydrolase was applied as an external selection pressure to resolve the fittest constituents of the system, where the optimal thiolesters were continuously hydrolyzed to acid and thiol products. During... 

There are various forms of tautomerism which operate in the different purine species. (1) Prototropy which involves attachment of the proton to any one of the four ring nitrogen atoms (Scheme 5). Corresponding CH tautomers, for example (52), seem to be of little significance. (2) Amine-imine tautomerism which operates in the aminopurines such as adenine (Scheme 6). (3) Lactam-lactim tautomerism as in the hydroxypurines such as hypoxanthine (Scheme 7) and the related thioxo-thiol tautomerism (53) and (54) in the biologically important mercaptopurines (Scheme 8). The subject has recently been discussed in some detail (76AHC(S1)502>. 

The choice of working electrode material is an important factor in amperometric detection. For catechols and similar substances, such as phenolic acids, electrodes made of glassy carbon have shown good performances. Other good detectable and biological important substances include thiols and disulfides (e.g., cysteine, glutathione, and their disulfides which... 

Organic compounds may be determined by redox titrimetry, including glucose and other reducing sugars, vitamin C, thiols such as cysteine, and many other organic chemicals of biological importance. There are thousands of potentiometric redox titration methods published in the chemical literature. 

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