ROS

Question 1

Formation of superoxide anion radical related to the ETC or cytochromes

Answer 1

If the one e- reduced form of CoQ (CoQH*) accidentally comes into contact with dissolved O2 it can transfer an e- to it, thereby generating the superoxide.

Question 2

Ionising Radiation generation of Hydroxyl radical

Answer 2

IR- generates highly reactive free radicals via H2O

Question 3

Haber-Weiss rxn generation of Hydroxyl radical

Answer 3

Hydrogen peroxide + Superoxide -> Hydroxyl radical

• non-enzymatic rxn
• transition metal e.g. Fe2+ or Cu2+ can catalyze rxn

Question 4

Fenton rxn generation of Hydroxyl radical

Answer 4

Hydrogen peroxide -> Hydroxyl radical + hydroxyl ion

• Requre Fe2+
• As free metals can initiate this rxn, therefore usually protein bound and found in trace amounts only
• Crush injuries tend to release Fe2+ from storage sites & generate high levels of free radical injury

Question 5

ROS damage on protein

Answer 5

• Exposure of proteins to ROS causes gross structural mods -> spontaneous fragmentation or increased proteolysis (Pro, His, Arg, Cys, Met particularly susceptible)
• Oxidised aa can also form abnormal cross-links with other residues. CYS cross-linking can prevent the degradation of aggregated proteins.

Question 6

ROS damage on DNA

Answer 6

2’-deoxyguanosine -> oxidation -> 8-hydroxy-2’-deoxyguanosine (biomarker for DNA oxidation; cancer) -> results in mis-pairing of G with A

Question 7

ROS damange on lipids

Answer 7

Lipid peroxidation also produces toxic aldehydes including malondialdehyde which can damage DNA by forming bulky adducts with G, A, and C.

Question 8

SOD-1 scavening of ROS

Answer 8

• catalyzes dismutation (reversal) of superoxide back to O2
• 3 isoforms:
  o Cytosolic
  o Mitochondrial
  o Extracell: increased by chemicals or conditions that increase the production of superoxide

Question 9

Catalase scavening of ROS

Answer 9

• Found principally in peroxisomes & to a lesser extent in cytosol & microsomal fractions of cell extracts
• H202 once formed must be reduced to H20 to prevent it from forming the hydroxyl radical in the Fenton or Haber-Weiss rxn.
• highest activity found in liver & kidney due to high numbers of peroxisomes
• in cells of immune system, catalase serves to protect the cell against its own respiratory burst

Question 10

Glutathione scavenging of ROS

Answer 10

• Glutathione Reductase:
• Glutathione Peroxidase:
  
  • requires Selenium
  • detox peroxide into water

Question 11

ROS formation as an immunological response

Answer 11

• Major source of deliberate production of ROS & RNOS by neutrophils in order to kill invading microorganisms.
• NOS isoform II: inducible; present in many of the immune systems cells (with similar lineage) such as macrophages & brain astroglia
  
  • Only expressed during infection
  • Uses Arginine as reactant to produce NO + Citrulline
  • NO* induces NADPH Oxidase activity to generate other cytocidal ROS & RNOS