Redox Biology I Flashcards
Which reaction do oxidoreductases catalyse?
Net transfer of electronsto or from a substrate
What kinds of enzymes are classes as oxidoreductases?
- Dehydrogenases
- Oxidases
- Reductases
How are reactive oxygen species formed?
By slippage in the ETC
What are the major sites for ROS production?
- Complex 1
- Complex 2
- Complex at FMN and quionine binding sites
What non-respiratory enzymes can also produce ROS?
eNOS and xanthine oxidase
How can ROS be produced in an inorganic way?
- Ionising radiation
- Environmental stress
What are ROS particularly damaging to?
- Fe-S clusters
- DNA
Why are ROS damaging to DNA?
They can cause unwanted disulfide bond formation
What electronic state does oxygen have?
Triplet ground state
What is interesting about the z electrons in oxygen?
They are unpaired with the same spin
Why is OH· so bad?
It can react with anything
Give examples of enzymes which shield us from ROS
- Superoxide dismutase
- Catalase
What reaction does superoxide dismutase catalyse?
2O2 + 2H+ → O2 + H2O
What are the 3 forms of superoxide dismutase?
- MnSOD
- CuZnSOD
- NiSOD
What is the superoxide dismutase reaction 2nd order with respect to?
Superoxide
What reaction does catalase catalyse?
2H2O2 → 2H2O +O2
What is the major small molecule anti-oxidant?
Glutathione
What 3 amino acids make up glutathione?
Glutamate, cysteine, glycine
Which form of glutathione is linked by a disulfide bond?
oxidised GSSG
Which enzyme maintains cellular glutathione?
Glutathione reductase
What induces glutathione reductase?
Oxidative stress
What does glutathione reductase use to reduce the disulfide bond of GSSG?
NADPH
What cofactor does glutathione reductase rely on?
FAD
What reaction does glutathione reductase catalyse?
2GSSG + NADPH +H+ → 2GSH + 2NADP+
What do glutathione peroxidases protect against?
Damage by H2O2
What is unusual about glutathione peroxidases?
It contains selenocysteine
What reaction does glutathione peroxidase catalyse?
2GSH + H2O2 → GSSG + 2H2O
What do the Grx family of enzymes do?
- Help to maintain cellular redox balance by reducing or oxidising bonds in other proteins
Which enzyme is involved in protection of damage from lipid hydroperoxidases?
GPx4
Which vitamins are maintained in their active state by glutathione?
- Vitamin C
- Vitamin E
- Vitamin A
Why are carotenoids useful in plants?
They help protect plants from oxidative damage to photosystems
What is beta-carotene susceptible to reaction with?
Single oxgen
How do plant-based carotenoids protect photosystems?
Dissipation of excitation as heat
What is the role of vitamin C in radical protection?
It acts as a radical scavenger which can also initiate free radical chain reactions