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Table 6 Antioxidants: catalytic – enzymatic inactivation of free radicals.

From: Homocysteine and reactive oxygen species in metabolic syndrome, type 2 diabetes mellitus, and atheroscleropathy: The pleiotropic effects of folate supplementation

Enzymatic Antioxidants
SUPER OXIDE DISMUTASE (SOD)[O2 - + SOD → H2O2 + O2] ecSOD (extracellular) MnSOD (mitochondrial) CuZnSOD (intracellular)
CATALASE– Location: peroxisome [2H2O2 + catalase → 2 H2O + O2]
GLUTATHIONE PEROXIDASE– Location: mitochondrion – cytosol and systemic circulation. (Glutamyl-cysteinyl-glycine tripeptide) glutathione reduced -SH to the oxidized disulfide GSSG. (Glutathione peroxidase) [GSH + 2H2O2 → GSSG + H2O + O2] (Glutathione reductase) [GSSG → GSH] at the expense of [NADH → NAD+] and/or [NAD(P)H → NAD(P)+]
NOS (nitric oxide synthase).– Location: membrane Isoforms: (e)NOS (endothelial): good (n)NOS (neuronal): good (i)NOS (inducible-inflammatory): bad
O2 - and nitric oxide (NO) are consumed in this process with the creation of reactive nitrogen species (RNS). O2 - + NO → ONOO- (peroxynitrite) + tyrosine → nitrotyrosine. Nitrotyrosine reflects redox stress and leaves a measurable footprint. NO: the good; O2 -: the bad; ONOO-: the ugly [42]
Nonenzymatic Antioxidants
URIC ACID
VITAMIN A, VITAMIN C, and VITAMIN E
THIOLS: Sulfhydryl (-SH) containing molecules.
ALBUMIN: Is an antioxidant due to thiol containing compounds.
APOPROTEINS: Ceruloplasmin and transferrin. Bind copper and iron in forms which cannot participate in the Fenton reaction
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