Ascorbic Acid thiols

Superoxide can also be produced by other enzymes, such as the range of flavin oxidases located in peroxisomes, and by oxidation of certain compounds including ascorbic acid, thiols, and adrenaline in the presence of transition metal ions. The autoxidation of reduced transition metal can also generate the superoxide... 

Detoxication of reactive oxygen species is also possible through the action of several low-molecular-weight compounds. Some are soluble in water, such as ascorbic acid, thiols, pyruvate and urate, and some are lipid soluble, such as vitamin E and /5-carotone (1). 

Persulfate (41) reacts with transition metal ions (e.g. Ag, Fe21, Ti31) according to Scheme 3.42. Various other reduetants have been described. These include halide ions, thiols (e.g. 2-mercaptoethanol, thioglycolic acid, cysteine, thiourea), bisulfite, thiosulfate, amines (triethanolamine, tetramethylethylenediamine, hydrazine hydrate), ascorbic acid, and solvated electrons (e.g. in radiolysis). The mechanisms and the initiating species produced have not been fully elucidated for... 

Reduced scavenger capacity is deduced from studies demonstrating low plasma and cellular levels of antioxidants such as glutathione, vitamin E, thiols, magnesium and ascorbic acid, as well as reduced levels of scavenger enzymes such as neutrophil glutathione peroxidase and red cell superoxide dismutase (Lyons, 1991 Sinclair /., 1992). 

A number of reducing agents have been determined directly using tetrazolium salts. Thus, the analyses of reducing sugars,423,424 hydraz-ides, 425 sulfides and thiols,426 ascorbic acid,427,428 formaldehyde,429 L-... 

Tetrazolium salts can be reduced nonselectively by many endogenous reductants such as thiol-containing proteins, as well as exogenous ones such as ascorbic acid.521 -523 This can lead to serious interferences and several measures have been described to reduce or eliminate their effect.524,525,650... 

The anticancer activity of platinum(IV) complexes, and the belief that reduction is needed to initiate this activity, had generated substantial interest in the rates and mechanism of reduction by biologically relevant reductants such as thiols, ascorbic acid, and methionine. Reduction of platinum(IV) to platinum(II) usually proceeds as a single two-electron step and is usually first-order with respect to both platinum(IV) and reductant concentrations. 

Polymer-supported catalysts often have lower activities than the soluble catalysts because of the intraparticle diffusion resistance. In this case the immobilization of the complexes on colloidal polymers can increase the catalytic activity. Catalysts bound to polymer latexes were used in oxidation reactions, such as the Cu-catalyzed oxidation of ascorbic acid,12 the Co-catalyzed oxidation of tetralin,13 and the CoPc-catalyzed oxidation of butylphenol14 and thiols.1516 Mn(III)-porphyrin bound to colloidal anion exchange resin was... 

Reduction of nitroxides to diamagnetic products may be brought about by such species as hydrazines, hydroxylamines, thiols, and ascorbic acid. The... 

Peroxynitrite is a very reactive species capable of reacting with many biomolecules including the antioxidants ascorbic acid, vitamin E, and uric acid [97-99], thiols [100], DNA [101], phospholipids [102], etc (see later). Because of this, a great interest has been drawn to the mechanisms of peroxynitrite reactions. 

The superoxo-containing species [(NC)6Co(/u.-02)Co(CN5]5 can be reduced with thiols such as 2-aminoethanethiol or L-cysteine (175), and the reduction reaction is catalyzed by copper(II) ions in aqueous solution. When copper(II) is present, the role of the thiol is to reduce cop-per(II) to copper(I), which then reacts with the superoxo species through an inner-sphere mechanism. Conversely, when the superoxo complex [(H3N)5Co(/x-02)Co(NH3)5]5+ is reduced with thiol (176), the reaction follows an outer-sphere mechanism, as would be expected. Ascorbic acid also reduces both complexes (177), but only the reduction of the cyano-containing complex exhibits copper(II) catalysis. 

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). 

Blood plasma of children with cystic fibrosis was found to have decreased TAC (by 16%) in spite of increased concentrations of ascorbic acid, uric acid, and thiol groups (L4). In another study TAC of children with cystic fibrosis was normal, but these children received vitamin supplementation in doses prescribed in international guidelines (a-tocopherol <10 years, 100 mg daily, and >10 years, 200 mg daily retinol 2.5 mg daily ascorbic acid 100-200 mg daily) (M2). Other authors found TAC values for nonhospitalized patients (1.40 0.20 mM) not different from laboratory control values (1.35 0.11 mM), but greater than values for hospitalized patients (1.09 0.17 mM). TAC in CF children correlated positively with anthropometric values (height, weight, body mass index) and pulmonary function (forced expiratory volume in 1 sec), but not with age (L3). 

GSH has been proposed to be part of the thiol cycling in mammalian cells that may transduce oxidative stress redox signaling into the induction of many genes involved in proliferation, differentiation, and apoptosis [15], Studies with pure chemical systems have confirmed the reduction of V(V) maltol compounds by GSH or ascorbic acid [16], Putative glutathione transferase enzymes that bind vanadium have been isolated from an ascidian that accumulates vanadium in specialized cells to over 350 mM [17],... 

In addition to its function in thiol/disulfide exchange, Grx-1 also serves as an alternative electron donor to ribonucleotide reductase (Fernandes and Holmgren 2004), participates in deiodination of thyroxine to triiodothyronine (Takagi et al. 1989), and acts as a dehydroascorbate reductase for regenerating ascorbic acid (Washburn and Wells 1989). However, despite the potential role of Grx in... 

The HA polymer can be degraded nonenzymatically by a free radical mechanism,226 particularly in the presence of reducing agents such as thiols, ascorbic acid, ferrous, or cuprous ions. This mechanism of depolymerization requires the participation of molecular oxygen. The use... 

Oxidation of organic substrates (flavones, phenols, indoles, thiols, ascorbic acid, etc.) using Co(salen)/02 systems is often interpreted in terms of initial production of radicals by H-atom (or electron) abstraction by the Co(II)02 or Co(III)02Co(III) moieties (122-127) (cf. Scheme 2), Reaction 38. In some of the conditions used, for example in... 

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