ROS Flashcards
what are low concentrations of ROS for signalling cell vs. High concentrations that cause damage
Steady state intra cellular concentrations of 10^-7 to ^-8 M
or 10 to 100 nM
examples of radical ROS
superoxide anion O2.-
hydroxyl radical
peroxyl radical
alkoyxl radical
hydroperoxyl
examples of non radical ROS
hydrogen peroxide
hypochlorous acid
hypobromous acid
ozone
single oxygen
Electronic configuration of O2 that allows it to accept and donate electrons
Oxygen has 6 valence electrons (the electrons in the outermost shell: 2s² 2p⁴).
oxygen has only four electrons in 2p:
According to Hund’s rule, electrons will occupy separate orbitals before pairing.
The three 2p orbitals (2p_x, 2p_y, and 2p_z) distribute the electrons as ↑ ↑ ↑ ↓, meaning two orbitals have one electron each, and the third orbital has a pair.
Paramagnetic Nature: Since oxygen has two unpaired electrons in the 2p orbitals, it is paramagnetic, meaning it is attracted to a magnetic field.
stable diradical
The hydroxyl radical (how is it formed and half life)
Three election deduction of o2 by the Fenton reaction. Short half life of 10-9, does not diffuse from the site generated
Superoxide radical (how is it formed? Reactions? Diffusion?)
Formed by a 1 electron oxidation of O2
Less reactive than hydroxyl radical, will only react quickly with note if oxide and iron sulfur clusters on certain enzymes
Cannot pass through membranes but can pass through some anion exchange protiens in erythrocytes and some lung cells
Hydrogen peroxide (how it’s formed? Half life and diffusion?)
Formed through the 2 electron reduction of o2
Can easily cross the cellular membrane through aquaporins and peroxiporins
Important signalling molecule
Half life is —
What is the Fenton reaction
Hydrogen peroxide can produce hydroxyl radicals through interactions with superoxide or divlaent cations Fe+2, Cu+2
How does the ETC produce radicals
§ Leakage of electrons can take place in complexes I and III, and sometimes complex II in some tissues (brown fat, muscle, brain in mice, insect flight muscles)
□ Most are generated from complex 1 and released into the matrix, some come from complex III into the intermembrane space
□ In the mitochondrial ETC, complex I and in part complex II release O2 ·−/H2 O2 towards the mitochondrial matrix, whereas release from complex III is towards the cristae lumen and the intermembrane space (Sies and Jones)
□ Most O∙− generated in mitochondria (e.g. from complex I) is released into the 2 matrix, but some of that from complex III into the intermembrane space
§ Estimated a intramitochondrial superoxide concentration of 10^-11 to 10^-12 M during normal respiration
Estimated __ % of oxygen consumed by the mitochondria contribute to electron leakage and ROS production
○ An estimated 2% of total oxygen consumed in the mitochondria, under normal physiological conditions, contributes to electron leakage and ROS production54.
Halliwell commentary - Often cited that 1-3% of the O2 consumed by mitochondria may form superoxide, the true rate may be lower (maybe 0.1–0.2%), due to these experiments carried out in exposed room air, which is hyperoxic
What does xanthine oxidase do
Minor contribution of cellular ROS
Produces super oxide during catalytic conversions of carbine to uric acid (purine metabolism)
RoS produced during fatty acid beta oxidation
Beta oxidation –> still being investigated, may be due to increased electron leakage from the ETC,
RoS produced by peroxidomes
Peroxisomes contain peroxisomal oxidases such as urate oxidases, glycolate oxidases, D-amino oxidases, L-α-hydroxyacid oxidases and fatty acyl-CoA oxidases, all of which can generate H2O2 when oxidizing a variety of substrates in peroxidative reactions
RoS produced by auto oxidation
Cellular molecules can undergo autooxidation, generating superoxide and hydrogen peroxide, some examples include catecholamines, flavins and thiols59.
The catecholamine neurotransmitter, dopamine, can autoxidize, and has been shown to be a contributing mechanism to neuronal degeneration in Parkinsons’ disease60
How does ionizing radiation generate RoS
Ionizing radiation and ultra violet radiation elevate the cellular energy, this is absorbed by water resulting in the breakage of the covalent oxygen-hydrogen bonds
How are RoS generated during tissue infection or tissue injury?
Tissue infection:NADPH Oxidase (NOX) Activation in Phagocytes
Tissue injury: During reperfusion, oxygen is rapidly restored, causing a burst of mitochondrial ROS due to electron transport chain overload.
How does xenobiotics generate RoS? Examples
How does redox cycling generate RoS
At the biochemical level, how does H2O2 regulate physiological processes?
oxidative damage to DNA – how many lesions?
20+ lesions
Oxidatie DNA damage results in - what type of lesions
oxidized bases, oxidized sugar fragments (C1-C5 prime radicals) abasic/apurinic/apryimidinic sites and SSBs
also hxydroalx radicals can damage nuclear protiens –> bind to DNA to form cross links
oxidative damage to proteins – targets?
hydorxl radicals targets aldehydes and ketons on the side chains of lysine, ariginine, proline, and threonine forming an irreversible caronyl group – impacting strucutre and function
and can form alpha carbon of amina acids, generating a carbon centered radical
oxidative damage to lipids - 2 byproducts examples and targets
2 byproducts formed are malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE)
hydroxyl radicals target carbon-carbon double bonds on polyunsaturated sats within the lipids, hydrogen abstraction creates a lipid radical – chain reaction of generating more lipid radicals
