Antioksidan: Béda antarrépisi
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Kaca anyar: thumb|right|350px|Modél eusi-rohang [[métabolomika|métabolit glutation antioksidan. Nu kelir konéng nunjukkeun atom walirang [[rédoks|aktif-... |
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Baris ka-6:
Kusabab strés oksidatif loba patalina jeung [[patogenesis]] kasakit manusa, antioksidan loba ditalungtik dina [[farmakologi]], utamana pikeun natambaan [[struk]] jeung [[kasakit neurodegeneratif]]. Antioksidan ogé sok ditambahkeun dina katuangan pikeun miara kaséhatan jeung nyegah sarupaning kasakit [[kangker]] jeung [[kasakit jantung koronér]]. Najan studi-studi nunjukkeun kauntungan pikeun kaséhatan, [[uji coba klinis]] teu manggihan kauntungan tina formulasi anu diuji, malah mun kaleuleuwihi mah bisa bahya. Di sagigireun mangpaatna pikeun kaséhatan, antioksidan loba gunana di dunya industri, misalna baé [[pangawét|ngawétkeun]] katuangan jeung kosmétik sarta nyegah dégradasi [[karét]] jeung [[béngsin]].
== Métabolit ==
Dumasar kaleyuranana, antioksidan dibagi dua rupa: leyur dina [[cai]] ([[hidrofil]]ik) atawa dina [[lipid]] ([[hidrofob]]ik). Sacara umum, antioksidan nu leyur-cai meta jeung oksidan dina [[sitoplasma]] sél jeung [[plasma getih]], sedengkeun antioksidan nu leyur-lipid nyegah [[mémbran sél]] tina panarajang [[peroksidasi]] lipid<ref name=Sies/>. Sanyawaan ieu bisa disintésis di jero awak atawa diserep tina katuangan<ref name=Vertuani/>. Rupa-rupa antioksidan aya dina kadar nu béda-béda dina cairan awak jeung jaringan. Misalna waé [[glutation]] atawa [[ubiquinon]] lolobana aya di jero sél, sedengkeun [[asam urat]] ampir rata di sakuliah awak (tempo tabél di handap).
Kapentingan jeung interaksi antara rupa-rupa antioksidan téh pajeulit, boga [[sinérgi]] jeung silih pangaruhan katergantungan antara hiji métabolit jeung nu séjénna sarta sistem-sistem énzimna<ref>{{cite journal |author=Chaudière J, Ferrari-Iliou R |title=Intracellular antioxidants: from chemical to biochemical mechanisms |journal=Food Chem Toxicol |volume=37 |issue=9–10 |pages=949 – 62 |year= |pmid=10541450}}</ref><ref>{{cite journal |author=Sies H |title=Strategies of antioxidant defense |journal=Eur J Biochem |volume=215 |issue=2 |pages=213 – 9 |year=1993 |pmid=7688300}}</ref>. Peta hiji antioksidan bisa jadi gumantung kana fungsi anggota séjén dina sistem antioksidan<ref name=Vertuani/>. Ku kituna, panyalindungan anu disadiakeun ku hiji antioksidan téh gumantung kana kadarna, réaktivitasna ka sajenis spésiés oksigén réaktif, sarta status antioksidan séjén anu aub dina réaksina<ref name=Vertuani/>.<!--
Some compounds contribute to antioxidant defense by [[chelation|chelating]] [[transition metal]]s and preventing them from catalyzing the production of free radicals in the cell. Particularly important is the ability to sequester iron, which is the function of [[iron-binding proteins]] such as [[transferrin]] and [[ferritin]].<ref>{{cite journal |author=Imlay J |title=Pathways of oxidative damage |journal=Annu Rev Microbiol |volume=57 |issue= |pages=395–418 |year= |pmid=14527285}}</ref> [[Selenium]] and [[zinc]] are commonly referred to as antioxidant nutrients, but these [[chemical element]]s have no antioxidant action themselves and are instead required for the activity of some antioxidant enzymes, as is discussed below.
{| class="wikitable" style="margin-left: auto; margin-right: auto;"
!Antioxidant metabolite
!Solubility
!Concentration in human serum (μM)<ref>{{cite journal |author=Ames B, Cathcart R, Schwiers E, Hochstein P |title=Uric acid provides an antioxidant defense in humans against oxidant- and radical-caused aging and cancer: a hypothesis |url=http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=349151&blobtype=pdf| journal=Proc Natl Acad Sci U S A |volume=78 |issue=11 |pages=6858 – 62 |year=1981 |pmid=6947260}}</ref>
!Concentration in liver tissue (μmol/kg)
|-
|align="center" |[[Ascorbic acid]] (vitamin C)
|align="center" |Water
|align="center" |50 – 60<ref>{{cite journal |author=Khaw K, Woodhouse P |title=Interrelation of vitamin C, infection, haemostatic factors, and cardiovascular disease |url=http://www.bmj.com/cgi/content/full/310/6994/1559 |journal=BMJ |volume=310 |issue=6994 |pages=1559 – 63 |year=1995 |pmid=7787643}}</ref>
|align="center" |260 (human)<ref name=Evelson>{{cite journal |author=Evelson P, Travacio M, Repetto M, Escobar J, Llesuy S, Lissi E |title=Evaluation of total reactive antioxidant potential (TRAP) of tissue homogenates and their cytosols |journal=Arch Biochem Biophys |volume=388 |issue=2 |pages=261 – 6 |year=2001 |pmid=11368163}}</ref>
|-
|align="center" |[[Glutathione]]
|align="center" |Water
|align="center" |325 – 650<ref>{{cite journal |author=Chen C, Qu L, Li B, Xing L, Jia G, Wang T, Gao Y, Zhang P, Li M, Chen W, Chai Z |title=Increased oxidative DNA damage, as assessed by urinary 8-hydroxy-2'-deoxyguanosine concentrations, and serum redox status in persons exposed to mercury |url=http://www.clinchem.org/cgi/content/full/51/4/759 |journal=Clin Chem |volume=51 |issue=4 |pages=759 – 67 |year=2005 |pmid=15695327}}</ref>
|align="center" |6,400 (human)<ref name=Evelson/>
|-
|align="center" |[[Lipoic acid]]
|align="center" |Water
|align="center" |0.1 – 0.7<ref>{{cite journal |author=Teichert J, Preiss R |title=HPLC-methods for determination of lipoic acid and its reduced form in human plasma |journal=Int J Clin Pharmacol Ther Toxicol |volume=30 |issue=11 |pages=511 – 2 |year=1992 |pmid=1490813}}</ref>
|align="center" |4 – 5 (rat)<ref>{{cite journal |author=Akiba S, Matsugo S, Packer L, Konishi T |title=Assay of protein-bound lipoic acid in tissues by a new enzymatic method |journal=Anal Biochem |volume=258 |issue=2 |pages=299 – 304 |year=1998 |pmid=9570844}}</ref>
|-
|align="center" |[[Uric acid]]
|align="center" |Water
|align="center" |200 – 400<ref>{{cite journal |author=Glantzounis G, Tsimoyiannis E, Kappas A, Galaris D |title=Uric acid and oxidative stress |journal=Curr Pharm Des |volume=11 |issue=32 |pages=4145 – 51 |year=2005 |pmid=16375736}}</ref>
|align="center" |1,600 (human)<ref name=Evelson/>
|-
|align="center" |[[Carotene]]s
|align="center" |Lipid
|align="center" |[[carotene|β-carotene]]: 0.5 – 1<ref>{{cite journal |author=El-Sohemy A, Baylin A, Kabagambe E, Ascherio A, Spiegelman D, Campos H |title=Individual carotenoid concentrations in adipose tissue and plasma as biomarkers of dietary intake |journal=Am J Clin Nutr |volume=76 |issue=1 |pages=172 – 9 |year=2002 |pmid=12081831}}</ref>
[[retinol]] (vitamin A): 1 – 3<ref name=Sowell>{{cite journal |author=Sowell A, Huff D, Yeager P, Caudill S, Gunter E |title=Retinol, alpha-tocopherol, lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, trans-beta-carotene, and four retinyl esters in serum determined simultaneously by reversed-phase HPLC with multiwavelength detection |url=http://www.clinchem.org/cgi/reprint/40/3/411.pdf?ijkey=12d7f1fb0a06f27c93b282ad4ea3435c0fb78f7e |journal=Clin Chem |volume=40 |issue=3 |pages=411 – 6 |year=1994 |pmid=8131277}}</ref>
|align="center" |5 (human, total carotenoids)<ref>{{cite journal |author=Stahl W, Schwarz W, Sundquist A, Sies H |title=cis-trans isomers of lycopene and beta-carotene in human serum and tissues |journal=Arch Biochem Biophys |volume=294 |issue=1 |pages=173 – 7 |year=1992 |pmid=1550343}}</ref>
|-
|align="center" |[[tocopherol|α-tocopherol]] (vitamin E)
|align="center" |Lipid
|align="center" |10 – 40<ref name=Sowell/>
|align="center" |50 (human)<ref name=Evelson/>
|-
|align="center" |[[Coenzyme Q|Ubiquinol]] (coenzyme Q)
|align="center" |Lipid
|align="center" |5<ref>{{cite journal |author=Zita C, Overvad K, Mortensen S, Sindberg C, Moesgaard S, Hunter D |title=Serum coenzyme Q10 concentrations in healthy men supplemented with 30 mg or 100 mg coenzyme Q10 for two months in a randomised controlled study |journal=Biofactors |volume=18 |issue=1 – 4 |pages=185 – 93 |year=2003 |pmid=14695934}}</ref>
|align="center" |200 (human)<ref name=Turunen>{{cite journal |author=Turunen M, Olsson J, Dallner G |title=Metabolism and function of coenzyme Q |journal=Biochim Biophys Acta |volume=1660 |issue=1 – 2 |pages=171 – 99 |year=2004 |pmid=14757233}}</ref>
|}
===Ascorbic acid===
[[Ascorbic acid]] or "[[vitamin C]]" is a [[monosaccharide]] antioxidant found in both animals and plants. As it cannot be synthesised in humans and must be obtained from the diet, it is a [[vitamin]].<ref>{{cite journal |author=Smirnoff N |title=L-ascorbic acid biosynthesis |journal=Vitam Horm |volume=61 |issue= |pages=241 – 66 |year= |pmid=11153268}}</ref> Most other [[animal]]s are able to produce this compound in their bodies and do not require it in their diets.<ref>{{cite journal |author=Linster CL, Van Schaftingen E |title=Vitamin C. Biosynthesis, recycling and degradation in mammals |journal=FEBS J. |volume=274 |issue=1 |pages=1-22 |year=2007 |pmid=17222174}}</ref> In cells, it is maintained in its reduced form by reaction with glutathione, which can be catalysed by [[protein disulfide isomerase]] and [[glutaredoxin]]s.<ref name=MeisterA>{{cite journal |author=Meister A |title=Glutathione-ascorbic acid antioxidant system in animals |journal=J Biol Chem |volume=269 |issue=13 |pages=9397 – 400 |year=1994 |pmid=8144521}}</ref><ref>{{cite journal |author=Wells W, Xu D, Yang Y, Rocque P |title=Mammalian thioltransferase (glutaredoxin) and protein disulfide isomerase have dehydroascorbate reductase activity |url=http://www.jbc.org/cgi/reprint/265/26/15361 |journal=J Biol Chem |volume=265 |issue=26 |pages=15361 – 4 |year=1990 |pmid=2394726}}</ref> Ascorbic acid is a [[reducing agent]] and can reduce and thereby neutralize reactive oxygen species such as hydrogen peroxide.<ref>{{cite journal |author=Padayatty S, Katz A, Wang Y, Eck P, Kwon O, Lee J, Chen S, Corpe C, Dutta A, Dutta S, Levine M |title=Vitamin C as an antioxidant: evaluation of its role in disease prevention |url=http://www.jacn.org/cgi/content/full/22/1/18 |journal=J Am Coll Nutr |volume=22 |issue=1 |pages=18 – 35 |year=2003 |pmid=12569111}}</ref> In addition to its direct antioxidant effects, ascorbic acid is also a [[substrate (biochemistry)|substrate]] for the antioxidant enzyme [[ascorbate peroxidase]], a function that is particularly important in stress resistance in plants.<ref>{{cite journal |author=Shigeoka S, Ishikawa T, Tamoi M, Miyagawa Y, Takeda T, Yabuta Y, Yoshimura K |title=Regulation and function of ascorbate peroxidase isoenzymes |url=http://jxb.oxfordjournals.org/cgi/content/full/53/372/1305 |journal=J Exp Bot |volume=53 |issue=372 |pages=1305 – 19 |year=2002 |pmid=11997377}}</ref>
===Glutathione===
[[Image:Lipid peroxidation.svg|thumb|350px|right|The [[Radical (chemistry)|free radical]] mechanism of [[lipid peroxidation]].]]
[[Glutathione]] is a [[cysteine]]-containing [[peptide]] found in most forms of aerobic life.<ref name=MeisterB>{{cite journal |author=Meister A, Anderson M |title=Glutathione |journal=Annu Rev Biochem |volume=52 |issue= |pages=711 – 60 |year= |pmid=6137189}}</ref> It is not required in the diet and is instead synthesized in cells from its constituent [[amino acid]]s.<ref>{{cite journal |author=Meister A |title=Glutathione metabolism and its selective modification |url=http://www.jbc.org/cgi/reprint/263/33/17205.pdf |journal=J Biol Chem |volume=263 |issue=33 |pages=17205 – 8 |year=1988 |pmid=3053703}}</ref> Glutathione has antioxidant properties since the [[thiol]] group in its cysteine moiety is a reducing agent and can be reversibly oxidized and reduced. In cells, glutathione is maintained in the reduced form by the enzyme [[glutathione reductase]] and in turn reduces other metabolites and enzyme systems as well as reacting directly with oxidants.<ref name=MeisterA/> Due to its high concentration and its central role in maintaining the cell's redox state, glutathione is one of the most important cellular antioxidants.<ref name=MeisterB/>
===Melatonin===
[[Melatonin]] is a powerful antioxidant that can easily cross [[cell membrane]]s and the [[blood-brain barrier]].<ref>{{cite journal |author=Reiter RJ, Carneiro RC, Oh CS |title=Melatonin in relation to cellular antioxidative defense mechanisms |journal=Horm. Metab. Res. |volume=29 |issue=8 |pages=363-72 |year=1997 |pmid=9288572}}</ref> Unlike other antioxidants, melatonin does not undergo [[redox cycling]], which is the ability of a [[molecule]] to undergo repeated [[reduction (chemistry)|reduction]] and [[oxidation]]. Redox cycling may allow other antioxidants (such as [[vitamin C]]) to act as [[pro-oxidant]]s and promote [[free radical]] formation. Melatonin, once oxidized, cannot be reduced to its former state because it forms several stable end-products upon reacting with free radicals. Therefore, it has been referred to as a terminal (or suicidal) antioxidant.<ref name="Tan2000">{{cite journal |author=Tan DX, Manchester LC, Reiter RJ, Qi WB, Karbownik M, Calvo JR |title=Significance of melatonin in antioxidative defense system: reactions and products |journal=Biological signals and receptors |volume=9 |issue=3–4 |pages=137-59 |year=2000 |pmid=10899700}}</ref>
===Tocopherols and tocotrienols (vitamin E)===
Vitamin E is the collective name for a set of eight related [[tocopherol]]s and [[tocotrienol]]s, which are fat-soluble antioxidant vitamins.<ref name=Herrera>{{cite journal |author=Herrera E, Barbas C |title=Vitamin E: action, metabolism and perspectives |journal=J Physiol Biochem |volume=57 |issue=2 |pages=43 – 56 |year=2001 |pmid=11579997}}</ref> Of these, α-tocopherol has been most studied as it has the highest [[bioavailability]], with the body preferentially absorbing and metabolising this form.<ref name=Brigelius>{{cite journal |author=Brigelius-Flohé R, Traber M |title=Vitamin E: function and metabolism |url=http://www.fasebj.org/cgi/content/full/13/10/1145 |journal=FASEB J |volume=13 |issue=10 |pages=1145 – 55 |year=1999 |pmid=10385606}}</ref> The α-tocopherol form is the most important lipid-soluble antioxidant and protects cell membranes against oxidation by reacting with the lipid radicals produced in the [[lipid peroxidation]] [[chain reaction]].<ref name=Herrera/> This removes the free radical intermediates and prevents the propagation reaction from continuing. The oxidised α-tocopheroxyl radicals produced in this process may be recycled back to the active reduced form through reduction by ascorbate, retinol or ubiquinol.<ref>{{cite journal |author=Wang X, Quinn P |title=Vitamin E and its function in membranes |journal=Prog Lipid Res |volume=38 |issue=4 |pages=309 – 36 |year=1999 |pmid=10793887}}</ref> The functions of the other forms of vitamin E are less well-studied, although γ-tocopherol is a [[nucleophile]] that may react with [[electrophile|electrophilic]] mutagens,<ref name=Brigelius/> and tocotrienols may have a specialised role in neuroprotection.<ref>{{cite journal |author=Sen C, Khanna S, Roy S |title=Tocotrienols: Vitamin E beyond tocopherols |url=http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1790869&blobtype=pdf |journal=Life Sci |volume=78 |issue=18 |pages=2088 – 98 |year=2006 |pmid=16458936}}</ref>
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== Baca ogé ==
* [[Téori radikal bébas]]
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