ROS Flashcards
Where are superoxides produced and how?
Complex III of the ETC–1 electron is delivered to O2 which is injected into the intermembrane space
Complex I can oleo generate superoxides—exclusively released into the matrix
What increases the production of superoxides?
High membrane potential—higher potential= slower transfer of electrons from Q to b site
High NADH/NAD ratio–causes over reduction of the ETC–more electrons available
ETC damage– increase in electron leak
Xenoiotics–MPTP blocks electron flow to the Q site and increases electron leak in Complex I
Electron backflow in Complex I– during ischemia–over-accumulation of succinate–rapidly oxidized by complex II–leading to over-reduction of Q site–drives electrons back through Complex I
What are the non-mitochondrial oxidases that generate ROSs?
NADPH oxidases—NADPH + 2O2–> NADP + 2O2- + H
Xanthine oxidase— Xanthine + O2–> Uric acid + O2- + H2O2—contribute to oxidative stress in ischemia/reperfusion injury
monoamine oxidase— Dopamine–> DOPAC + NH3 + H2O2
What does Xanthine oxidase contribute to?
Oxidative stress in ischemia/reperfusion injury
What does monoamine oxidase contribute to?
hypersensitivity of dopaminergic neurons to oxidative stress
How is H2O2 converted to the highly reactive OH?
Fenton reaction–transfers electron to H2O2 from free metal ions (Fe2+) which is then converted into Fe3+
recycled back to Fe2+ by reacting with O2-
How does DNA damage occur through ROS?
OH free radical generated through fenton reaction–OH extracts electrons from either sugar or base moieties–producing oxidative lesion such as 8-hydroxy-2’-deoxyguanosine–this can mispair with deoxyadenosine leading to G-to-T transversion —DNA damage–metagenesis and carcinogenesis
What is lipid peroxidation?
OH is highly active in mediating lipid oxidation–double bonds of arachindonic acid and linoleum acid–hydrogens close to double bonds highly reactive and prone to lose electron to OH–causing membrane damage
What does the breakdown of lipid peroxidation products produce?
Highly reactive aldehydes–malondialdehyde and 4-hydroxy-(2E)-nonenal
Used as biomarkers for lipid peroxidation
What can H2O2 react with and what does it cause?
thiol proteins–cysteine–get loss of activity and protein aggregation
Most of the damage that comes from H2O2 is from the Fenton reaction creating OH radicals
What does superoxide dismutase do?
Converts 2 molecules of O2- into one molecule of O2 and one of the less toxic H2O2
What is SOD-1 and where is it located? What do mutations to this cause?
Cu, Zn- SOD– cytosolic SOD
Mutations cause Amyotrophic Lateral Sclerosis (ALS)–misfolded and becomes ctotoxic–doesnt necessarily lose enzymatic activity
What is SOD-2 and where is it located?
Mn- SOD– mitochondrial SOD
O2- superoxide can cross the outer BUT NOT the inner membrane—Mn-SOD responsible for degrading superoxide in the mito matrix
What does Glutathione peroxidase (GSH) do?
Converts H2O2 to H2O
Electron rich functional group at cysteine bearing suflhydryl group
What regenerates GSH from GSSG and what is this reaction dependent on?
Glutathione reductase which is dependent on NADPH
Mito–TCA cycle produces NADPH
Erythrocytes– Pentose Phosphate pathway produces NADPH by glucose-6 phosphate dehydrogenase
What happens when there is a deficiency in glucose-6 phosphate dehydrogenase?
NADPH is NOT produced the convert GSSG back to GSH so oxidative strew occurs causing hemolytic anemia
What is peroxiredoxin pathway?
second mechanism for disposal of H2O2 important for detoxification of H2O2 in mito and erythrocytes
uses thioredoxin for 2nd/last step which is dependent on tioredoxin reductase which needs NADPH
What does catalase do?
H2O2 + H2O2 —-> H2O + H2O + O2
What are two common non-enzymatic antioxidants to scavenge ROS?
Coenzyme Q10
Vit E
What does Coenzyme Q10 (ubiquinone) do?
Non-enzymatic antioxidant that scavenge superoxides and inhibit lipid peroxidation
What is GSH/GSSG ratio used for?
indicator of redox balance of the cell
GSH»GSSG–reaction will move forward getting ride of ROS—disulfide linked protein breaks
GSH<GSSG– formation of inactive disulfide linked protein complexes is favored
What role does Vit E play in antioxidant activity?
protects membrane lipids and lipoproteins
What role does Vit C(ascorbate) play in antioxidant activity?
protects many molecules by reacting with a wide spectrum of radicals
What do plant phenols doe?
inhibit LDL oxidation
What do Flavonoids reduce the risk of?
Coronary heart dz and stroke
What are Physiological roles of ROS/RNOS
• Oxidative folding • Redox signaling for proliferation & differentiation • Innate immunity (e.g., phagocytes) • Inflammatory response • Would healing • Apoptosis
