Antioxidant Network Flashcards
3 defense against prooxidants
- prevent prooxidant formation: inhibit enzymes that produce ROS or chelate with metal ions that catalyze ROS
- intercept prooxidant: before damage is caused. donate e- or H+ to stabilize free radicals, convert to less reactive ( Vit C and E)
- repair damage from prooxidant: Superoxide dismutase (SOD), catalase, and glutathione peroxidase help convert ROS to harmless molecules like water and oxygen
classical antioxidant
intercepts reactive species once formed
prevents further damaging activity - chain breaking antioxidant
transfers reactive species from critical parts of cell, reduce risk of damaging intracellular components
phase 2 (antioxidant) enzymes
catalytically remove prooxidants: convert to less harmful substance (SOD, catalase, glutathione peroxidase)
conjugate for excretion (glucuronic acid, GSH, sulphate): make them more water-soluble and easier to excrete
Removal of superoxide (O2 radical), 2 ways
- superoxide dismutases (CuZn SOD and Mn SOD)
2 O2 radical + 2 H+ = H2O2 + O2
- keeps superoxide level low
- Vitamin C:
AH2 + O2 radical = ascorbyl radical + H2O2 hydrogen peroxide
Vit C is aqueous, in blood and cytoplasm
removal of hydrogen peroxide (H2O2)
Vit C:
AH2 + H2O2 = DHA + 2 H2O
Glutathione Peroxidase (GPx): 4 Selenium
uses GSH
high level in cells
SH thiol donor, donates H atom
helps preserve protein SH groups
2 GSH + H2O2 = GSSG + 2 H2O
removal of H2O2 with catalase
heme Fe enzyme
large amount in peroxisomes
also in cytoplasm, mito, and ER
high in WBC and RBC
2 H2O2 -> 2 H2O + O2
removal of OH radical (hydroxyl radical)
best to prevent formation from hydrogen peroxide (use GPx and catalase)
scavengers: Vit C, uric acid, dihydrolipoic acid DHLA, GSH, SH proteins (albumin, metallothionine)
need at a competitive concentration and readily donate e- bc Oh radicals are very reactive
AH2 + OH radical = H2O + AH radical
GSH + OH radical = H2O + GSSG
removal of singlet oxygen
Vit C:
AH2 + singlet O2 = AH radical + O2- superoxide anion + H+
carotenoids (beta, lycopene):
1. carotenoid + singlet O2 = excited state carotenoid + O2
2. excited carotenoid = carotenoid + heat
Removal of alkoxyl (RO), Peroxyl (ROO), and Lipid peroxyl (LOO) RADICALS
RO radical:
water soluble: Vit C, GSH
lipid soluble: Vit E, ubiQH2
RO radical + AH2 = ROH + AH radical
ROO radical
ROO + AH2 = ROOH + AH radical
what does antioxidant network do
catalytic maintenance of antioxidant defense
non-scavenging enzymes re reduce antioxidants
depend on energy status of cell for NADPH
BUT still leaves behind ROOH
antioxidant network 2 for hydroperoxides
ROOH to ROH
uses GPxase, Se
GSSG, NADPH, and G6P to regenerate GSH, GPxase, and 6-phosphogluconate
