Antioxidants Flashcards
what is the antioxidant system
the antioxidant system is a network of enzymatic and non-enzymatic molecules (2 main types) that protect cells from oxidative stress, which arises when ROS accumulate and damage cellular components
what are the enzymatic antioxidants
SOD (1,2,3)
Catalase
Glutahione peroxidase
Glutathion reductase
Peroxireodxins
Thioredoxin
What does SOD do and where is it located?
COnvers O2- to H2O2
SOD1 -> cytosol
SOD2 -> mitochondria
SOD3 -> extracellular
What does CAT do
Breaks down H2O2 to H2O and O2
located in peroxisomes
What does glutathione peroxidase do
reduced H2O2 and lipid peroxides
located in the mitochondria and cytosol
what does glutathione reductase do
regenerates reduced glutathione (GSH) in the cytosol
what does thioredoxins do
maintain redox homeostasis by reducing oxidized proteins
located in the cytosol and mitochondria
What are the 8 strategies that cell employs against oxidative damage
1) Enzymatic antioxidants
2) Nonenzymatic antioxidants
3) Compounds that control the formation of ROS, e.g. proteins that uncouple the ETC, proteins that sequester pro-oxidants like iron and copper ions
4) Agents that protect cellular macromolecules from oxidation, e.g. DNA chaperone proteins
5) Physical quenchers, e.g. carotenoids (for singlet O2)
6) Replacement of molecules sensitive to oxidative damage, e.g fumarase C in E. coli
7) Reaction with biomolecules to give products that are cytoprotective, e.g. products that terminate lipid peroxidation, e.g. vitamin E and coenzyme Q
Compartmentalization, e.g membranes to keep metal ions separated from H2O2
What does glutaredoxins (Grx) do
Thioredoxins (Trx) (EC 1.8.1.9) and glutaredoxins (Grx) (EC 1.20.4.1) are proteins that contain reduced thiol (R-SH) groups that are oxidized and converted to a disulfide (R-S-S-R) bond when reducing a target compound (Fig. 1.14)
Grx and Trx have overlapping functions in the repair of oxidatively damaged amino acid side chains in proteins by donating an electron thereby reducing itself.
Grx system is comprised of glutaredoxin, GSH, GSH reductase and NADPH (Holmgren, 1989).
What do peroxidedoxins do
Thioredoxins (Trx) (EC 1.8.1.9) and glutaredoxins (Grx) (EC 1.20.4.1) are proteins that contain reduced thiol (R-SH) groups that are oxidized and converted to a disulfide (R-S-S-R) bond when reducing a target compound (Fig. 1.14)
Grx and Trx have overlapping functions in the repair of oxidatively damaged amino acid side chains in proteins by donating an electron thereby reducing itself.
The Trx ‘system’ is composed of Trx, Trx reductase, and NADPH,
What does peroxiredoxins (Prx) do?
peroxiredoxins (Prx) are a class of H2O2 scavengers that are located primarily in the cytosol, but have also been identified in mitochondria, peroxisomes and nucleus. T
What is the role of GSH and what concentration is it found in the cell?
GSH is involved in many cellular functions, one of which is a cofactor for several enzymes, including glutathione peroxidase and glutathione S-transferases
3-10 mM
What is the role of Ascorbic acid and α-tocopherol? Where are they found
avenge free radicals directly and donate electrons to neutralize them50.
-Vitamin C is found in the cytosol a concentrations of 2-5 mM, electron donor
Vitamin E is found in the plasma membrane, donates to peroxyl radicals, prevents the propagation of lipid peroxidation
