Metabolites Antioxidant

1 metabolites

1.1 uric acid
1.2 vitamin c
1.3 glutathione
1.4 melatonin
1.5 vitamin e

metabolites

antioxidants classified 2 broad divisions, depending on whether soluble in water (hydrophilic) or in lipids (lipophilic). in general, water-soluble antioxidants react oxidants in cell cytosol , blood plasma, while lipid-soluble antioxidants protect cell membranes lipid peroxidation. these compounds may synthesized in body or obtained diet. different antioxidants present @ wide range of concentrations in body fluids , tissues, such glutathione or ubiquinone present within cells, while others such uric acid more evenly distributed (see table below). antioxidants found in few organisms , these compounds can important in pathogens , can virulence factors.

the relative importance , interactions between these different antioxidants complex question, various metabolites , enzyme systems having synergistic , interdependent effects on 1 another. action of 1 antioxidant may therefore depend on proper function of other members of antioxidant system. amount of protection provided 1 antioxidant depend on concentration, reactivity towards particular reactive oxygen species being considered, , status of antioxidants interacts.

some compounds contribute antioxidant defense chelating transition metals , preventing them catalyzing production of free radicals in cell. particularly important ability sequester iron, function of iron-binding proteins such transferrin , ferritin. selenium , zinc commonly referred antioxidant nutrients, these chemical elements have no antioxidant action , instead required activity of antioxidant enzymes, discussed below.

uric acid

uric acid far highest concentration antioxidant in human blood. uric acid (ua) antioxidant oxypurine produced xanthine enzyme xanthine oxidase, , intermediate product of purine metabolism. in land animals, urate oxidase further catalyzes oxidation of uric acid allantoin, in humans , higher primates, urate oxidase gene nonfunctional, ua not further broken down. evolutionary reasons loss of urate conversion allantoin remain topic of active speculation. antioxidant effects of uric acid have led researchers suggest mutation beneficial primates , humans. studies of high altitude acclimatization support hypothesis urate acts antioxidant mitigating oxidative stress caused high-altitude hypoxia.

uric acid has highest concentration of blood antioxidant , provides on half of total antioxidant capacity of human serum. uric acid s antioxidant activities complex, given not react oxidants, such superoxide, act against peroxynitrite, peroxides, , hypochlorous acid. concerns on elevated ua s contribution gout must considered 1 of many risk factors. itself, ua-related risk of gout @ high levels (415–530 μmol/l) 0.5% per year increase 4.5% per year @ ua supersaturation levels (535+ μmol/l). many of these aforementioned studies determined ua s antioxidant actions within normal physiological levels, , found antioxidant activity @ levels high 285 μmol/l.

vitamin c

ascorbic acid or vitamin c monosaccharide oxidation-reduction (redox) catalyst found in both animals , plants. 1 of enzymes needed make ascorbic acid has been lost mutation during primate evolution, humans must obtain diet; therefore vitamin. other animals able produce compound in bodies , not require in diets. ascorbic acid required conversion of procollagen collagen oxidizing proline residues hydroxyproline. in other cells, maintained in reduced form reaction glutathione, can catalysed protein disulfide isomerase , glutaredoxins. ascorbic acid redox catalyst can reduce, , thereby neutralize, reactive oxygen species such hydrogen peroxide. in addition direct antioxidant effects, ascorbic acid substrate redox enzyme ascorbate peroxidase, function particularly important in stress resistance in plants. ascorbic acid present @ high levels in parts of plants , can reach concentrations of 20 millimolar in chloroplasts.

glutathione

the free radical mechanism of lipid peroxidation.

glutathione cysteine-containing peptide found in forms of aerobic life. not required in diet , instead synthesized in cells constituent amino acids. glutathione has antioxidant properties since thiol group in cysteine moiety reducing agent , can reversibly oxidized , reduced. in cells, glutathione maintained in reduced form enzyme glutathione reductase , in turn reduces other metabolites , enzyme systems, such ascorbate in glutathione-ascorbate cycle, glutathione peroxidases , glutaredoxins, reacting directly oxidants. due high concentration , central role in maintaining cell s redox state, glutathione 1 of important cellular antioxidants. in organisms glutathione replaced other thiols, such mycothiol in actinomycetes, bacillithiol in gram-positive bacteria, or trypanothione in kinetoplastids.

melatonin

melatonin powerful antioxidant. melatonin crosses cell membranes , blood–brain barrier. unlike other antioxidants, melatonin not undergo redox cycling, ability of molecule undergo repeated reduction , oxidation. redox cycling may allow other antioxidants (such vitamin c) act pro-oxidants , promote free radical formation. melatonin, once oxidized, cannot reduced former state because forms several stable end-products upon reacting free radicals. therefore, has been referred terminal (or suicidal) antioxidant.

vitamin e

vitamin e collective name set of 8 related tocopherols , tocotrienols, fat-soluble vitamins antioxidant properties. of these, α-tocopherol has been studied has highest bioavailability, body preferentially absorbing , metabolising form.

it has been claimed α-tocopherol form important lipid-soluble antioxidant, , protects membranes oxidation reacting lipid radicals produced in lipid peroxidation chain reaction. removes free radical intermediates , prevents propagation reaction continuing. reaction produces oxidised α-tocopheroxyl radicals can recycled active reduced form through reduction other antioxidants, such ascorbate, retinol or ubiquinol. in line findings showing α-tocopherol, not water-soluble antioxidants, efficiently protects glutathione peroxidase 4 (gpx4)-deficient cells cell death. gpx4 known enzyme efficiently reduces lipid-hydroperoxides within biological membranes.

however, roles , importance of various forms of vitamin e presently unclear, , has been suggested important function of α-tocopherol signaling molecule, molecule having no significant role in antioxidant metabolism. functions of other forms of vitamin e less understood, although γ-tocopherol nucleophile may react electrophilic mutagens, , tocotrienols may important in protecting neurons damage.