Mito Function and Tox Ox Species--------------------------------- Flashcards
what are the major sources of ROS?
Mitochondrial electron transport chain Ionizing radiation Enzymes Phagocytes Endoplasmic drug metabolism (Cyt P450) Detoxification system in the liver (Cyt P450)
Which amino acids are particularly susceptible to ROS attack?
Amino acids particularly susceptible are:
Pro, His, Arg, Cys, Met
What are consequences of ROS attack on proteins?
Fragmentation, cross-linking, aggregation, susceptible to proteolytic digestion
What are consequences of ROS attack on lipids?
Membrane damage; aldehydes produced can cross-link proteins
What are consequences of ROS attack on DNA?
Strand breaks, base alteration
A large percentage of the superoxide formed in cells occurs in the _____? how so?
mitochondria; Mito has DNA that is relatively unprotected compared to nuclear DNA. So one is far more likely to encounter ROS damaged DNA in mito compared to nuclear DNA
how does oxidative stress occur?
When free radicals cause More damage more Quickly than our cells Can protect against or Repair.
what are the types of free radical mediated cellular injury due to oxidative stress?
protein damage membrane damage DNA damage mito damage cell swelling increased permeability massive influx of Ca2+ lipid peroxidation
what is oxidase?
an enzyme that promotes the transfer of a hydrogen atom from a particular substrate to an oxygen molecule, forming water or hydrogen peroxide
what is oxygenase?
any enzyme that oxidizes a substrate by transferring the oxygen from molecular oxygen O2 (as in air) to it.
What is formed when O2 picks up a single electron?
ROS, rapid oxygen species and this happens when oxidases, peroxidases, and oxygenases transfer a single electron to O2 via a metal
what is lipid peroxidation?
radical derived lipid oxidation results in oxidized breakdown products like a lipid peroxy radical rearranging lipid chain breaks producing malondialdehyde(marker for oxidative stress)
Describe electron leak when the O2 picks up the electron from the CoQH?
Why is it relevant for ROS formation?
Normally CoQ is bound to COMPLEX I and receives both electrons there. Leaves COMPLEX I in a fully reduced form.
Statistical possibility that CoQ will dissociate after receiving only 1 electron: semi-quinone radical form.
With high O2 levels in mitochondria, likelihood of superoxide formation is high;
Electrons can be picked readily and membrane, DNA, protein damage highly likely
how likely is mitochondrial DNA susceptible to ROS than nuclear DNA?
10x more susceptible
The nuclear DNA is protected by histones, is this the case for mitochondria?
no, mitochondria have lack of the protective histones.
what is there a high generation rate of from the mitochondrial ETC at the CoQ?
ROS generation
what is it important to note that mito DNA is also located near the inner membrane of mitochondria where the ETC is located?
ROS generated from ETC does not have to travel very far to attack the DNA.
Describe in detail the Cytochrome P450 system
a monoxygenase that uses molecular oxygen and splitting it in half and one oxygen ends up on substrate and another one ends up on water.
Key to reaction mechanism is formation of superoxide anion bound to the Fe3+ center. If this O2- escapes (red circle), it will be a free radical in solution.
NADPH is also used instead of NADH providing electrons
it becomes uncoupled when the O2- gets away instead of being held
what is the effect of the induction of Cyt 450 by drugs, alcohol and chemical toxicants?example?
increased cell injury due to increased free radical damage because of increased work by Cyt P450; parkinson’s disease
what is nitric oxide?
a radical species produced by vascular endothelium cells but for potential for damage can happen…if we are uncoupled in our endothelial cells with lots of superoxide produced at or around the membrane close to NO production and they can unite to form proxynitrite, also know as a reactive nitrogen species (strong oxidizing agent)
what is produced when superoxide and NO come together?
peroxynitrite, soluble molecule and destroys everything
free iron has potential to cause harm to the body how is it removed?
by binding to ferritin, protecting it from oxygen, another form, hemosiderin is same except it is larger
what are some other cellular defense mechanisms?
Vitamin E and Beta carotene and protect membrane of cells against free radicals
what is superoxide dismutase and catalase?
seek and destroy superoxide and H2O2
why is superoxide dismutase important?
diffusion limited enzyme which has a reaction mechanism that is faster than diffusion of superoxide which means if it found itself in the dismutase active site it is unable to escape and so it converts a 2O2-(due to its electron rearrangement) into an O2 and H2O2(not as reactive as superoxide)
why is catalase important?
grabs 2 H2O2 and rearrange it to produce 2 water and 2 O2s, shows up together with superoxide dismutase and they are independent of each other
what is glutathione peroxidase and glutathione reductase?
it takes H2O2 along with its reduced 2 GSH to produce 2 molecules of water and oxidized glutathione to 2 GSSG which has to be re-reduced and so you have glutathione reductase that uses power of NADPH that donates its electrons to produce 2 GSH
what are the types of superoxide dismutase?
Cu-Zn SOD (cytosolic)
Mn SOD (mitochondrial)
EC-SOD (extracellular
