Oxidative Stres pt. 2

Question 1

Reaction of oxygen free radicals

Answer 1

the first reaction of a hydroxyl radical is to remove a hydrogen atom from any molecules in the cells to generate water + alkyl radical the alkyl radical can then react with oxygen to form a peroxy radical

Question 2

hydroxyl radical is

Answer 2

highly reactive + short lived

Question 3

Mechanism of lipid peroxidation

Answer 3

1. attack on a species that can abstract a H from a methylene carbon on the side chain 2. H atom is now a free radical & it leaves behind a carbon center radical 3. in aerobic cells it undergoes molecular rearrangement 4. then reacts with O2 to generate a peroxy radical

Question 4

peroxy radicals can attack

Answer 4

membrane proteins; they are capable of abstracting hydrogen from adjacent fatty acid side chains in a membrane therefore PROPAGATING the chain reaction of lipid peroxidation

Question 5

length of lipid peroxidation propagation chain via peroxyl radicals is dependent on many factors

Answer 5

1. lipid/protein ratio in a membrane 2. fatty acid composition 3. oxygen concentration 4. presence within the membrane of chain-breaking antioxidants like AH which interrupt the chain reaction by providing easily-donatable hydrogen

Question 6

if two radicals react

Answer 6

both radicals are eliminated

Question 7

if a radical reacts with a nonradical

Answer 7

another radical will be produced

Question 8

which reactive species of oxygen initiate lipid peroxidation?

Answer 8

most involve transition metal ions the oxidized forms of these transition metal ions accelerate peroxidation if a reducing agent is present

Question 9

hydroxyl radical is almost always detectable in metal ion-dependent peroxidation systems; addition of catalase rarely inhibits the peroxidation observed

Answer 9

this indicates that the metal ions can react with lipid hydroperoxides present in the membrane preparation to produce lipid alkoxyl radicals and lipid radicals - both are capable of initiating the chain reaction of lipid peroxidation

Question 10

biological consequences of lipid peroxidation

Answer 10

1. impairment of membrane function 2. decreased fluidity 3. inactivation of membrane-bound receptor and enzymes 4. increased non-specific permeability to ions such as calcium **lipid radicals and lipid alkoxyl radicals(which are products of decomposition of lipid hydroperoxides) can abstract further hydrogen atoms from fatty acid chains**

Question 11

major aldehyde produced by lipid peroxidation is 4-hydroxynonenal (HNE), HNE is

Answer 11

cytotoxic in a dose-dependent manner to a broad spectrum of cells implicated in numerous forms of cell injury stimulates neutrophil chemotaxis modulate adenylate and guanylate cyclase activity stimulate phospholipases it’s genotoxic + carcinogenic + cause cell death

Question 12

another aldehyde generated by lipid peroxidation is malondialdehyde

Answer 12

can cause cross-linking, polymerization of membrane proteins alter intrinsic membrane properties like deformability, ion transport, enzyme activity, aggregation of cell surface determinants it’s diffusable - it can interact with nitrogenous bases of DNA it’s mutagenic + genotoxic + carcinogenic

Question 13

biological effects of aldehydes: 100micromolar

Answer 13

nonspecific cytotoxic effects leading to rapid cell death rapid depletion of glutathione, decrease in protein thiols, onset of lipid peroxidation, disturbance of Ca homeostasis, inhibition of DNA, RNA and protein synthesis, inhibition of respiration and glycolysis, lactate release (it’s unlikely it would actually reach this concentration)

Question 14

biological effects of aldehydes: 1-20micromolar

Answer 14

inhibit DNA and protein synthesis stimulate phospholipase A2 inhibit oncogene c-myc expression activate heat shock and heme oxygenase-1 gene expression **may all occur following oxidative stress**

Question 15

biological effects of aldehydes: <0.1micromolar

Answer 15

likely to occur at basal physiological level stimulation of chemotaxis modulation of adenylate cyclase activity weak stimulation of guanylate cyclase stimulation of phospholipase C

Question 16

Denaturation of proteins by aldehydes

Answer 16

aldehydes are long lived, so they diffuse

Question 17

Denaturation of proteins by aldehydes: HNE has 3 main functional groups

Answer 17

1. aldehyde group 2. CC double bond 3. hydroxyl group

Question 18

Denaturation of proteins by aldehydes: HNE readily is reacted with glutathione to form

Answer 18

a saturated aldehyde, this undergoes an intramolecular rearrangement to the 5-membered cyclic hemiacetal **the aldehyde groups of HNE are preserved in all conjugated amino acids - may undergo secondary reactions with the same amino groups of lysine residues of the same/different protein to yield intra- and inter-subunit cross-links via schiff base formation **

Question 19

the level of proteins that are conjugated with HNE is increased following

Answer 19

oxidative stress - representing a consequence of the increased lipid peroxidation

Question 20

Denaturation of proteins by aldehydes: malondialdehyde (MDA)

Answer 20

major aldehyde released by peroxidized lipids, known to react with the e-amino group of lysine residue in a protein to form unstable amino propenal & intra-/inter- protein imine adducts - this contributes to intra- or inter- protein cross-links

Question 21

Denaturation of proteins by aldehydes: MDA modified proteins induce

Answer 21

induce inflammatory responses and are recognized by the innate immune system found in atherosclerosis, age-related macular degeneration, other chronic degeneratie diseases

Question 22

clinical relevance of lipid peroxidation: age-related macular degeneration

Answer 22

medical condition which affects older people; results in loss of vision in the center of the visual field because of damage to the retina may partly result from many environmental and genetic factors such as tissue inflammation and oxidative stress due to cigarette smoking /light exposure

Question 23

Protein oxidation

Answer 23

generated by radiolysis and metal-catalyzed reactions

Question 24

oxidation of free amino acids residues in proteins by ionizing radiation

Answer 24

effects of ionizing radiation on amino acids and proteins in oxygenated solutions are mainly attributable to the formation of hydroxyl radial, peroxide radical and hydroperoxyl radical

Question 25

alphatic amino acids

Answer 25

leads to the formation of NH4+ and alpha ketoacids

Question 26

depletion of oxygen in reaction mixtures during radiolysis

Answer 26

may suppress the generation of peroxyl radical and favor reductive deamination as well as variety of carbon-centered radical combination interaction to form mono- & di-amino dicarboxylic acid derivatives

Question 27

aromatic amino acids

Answer 27

indole ring of tryptophan and aromatic group of tyrosine and phenylalanine are PRIMARY targets of oxygen radicals produced during radiolysis , alpha-hydrogen abstraction and deamination are relatively minor events

Question 28

Major product of tryptophan oxidation is

Answer 28

formylkynurenine

Question 29

oxidation of tyrosine forms

Answer 29

3,4-dihyroxyphenylalanine

Question 30

oxidation of phenylalanine leads to the production of

Answer 30

tyrosine and other hydroxy derivatives

Question 31

proteins in the absence of oxygen

Answer 31

there is little or no fragmentation of the protein but considerable amounts of high-molecular-weight aggregates are formed

Question 32

proteins in the presence of oxygen

Answer 32

little or no aggregation occurs but there is considerable fragmentation

Question 33

oxygen-mediated cleave of the polypeptide chain

Answer 33

occurs by the alpha-amidation pathway

Question 34

alpha hydrogen of amino acid residues (and methyl, methylene groups) in proteins are major sites of

Answer 34

hydroxyl attack

Question 35

proteins are mostly converted to what when exposed to radiolysis in the absence of oxygen?

Answer 35

converted to high-molecular weight aggregates - these aggregates are known to result from formation of inter-protein cross-linking reactions and from hydrophobic and electrostatic interactions

Question 36

metal-catalyzed oxidation(MCO) of amino acid residues in proteins: free amino acids

Answer 36

in the presence of Fe(III) or Cu(II), oxygen and an electron donor MCO systems are able to oxidize free amino acids and amino acid residues in proteins

Question 37

the MCO system with free amino acids includes

Answer 37

nonenzymatic systems and enzymatic systems (including NADPH dehydrogenase, xanthine oxidase, CYP450 reductases, quinone reductase)

Question 38

metal-catalyzed oxidation of amino acid residues in proteins: proteins

Answer 38

more than 40 proteins have been shown to be sensitive to metal-catalyzed reaction: His, Arg, Lys, Pro, Met and Cys are the most common

Question 39

metal-catalyzed oxidation of amino acid residues in proteins: only one or only a few amino acid residues in a given protein are modified by the MCO systems but how many amino acids are?

Answer 39

all amino acids are susceptiable to oxidation by free radicals generated during radiolysis

Question 40

carbonyl group

Answer 40

a functional group composed of a carbon atom double-bonded to an oxygen atom

Question 41

superoxide anion radical can act either as an

Answer 41

univalent oxidant or reductant

Question 42

superoxide anion radical - family of dehydrogenases contains clusters at their active sites, the group includes

Answer 42

alpha, beta-dihydroxyacid dehydratase, 6-phosphogluconate dehydrogenase and acontiase they undergo rapid oxidation by superoxide radical with a resultatnt loss of Fe(II) fromt eh cluster and concomitnat inactivation - inactivation affacts various pathways in cellular metabolism (like branched-chain amino acid synthesis, pentose phosphate pathway and tricarboxylic acid cycle)

Question 43

release of Fe(II) from the cluster sets the stage for the Fenton reaction

Answer 43

where a hydroxyl radical is produced this reaction is the basis for cooperation between superoxide and hydrogen peroxide to attack a variety of cellular targets also predicts the protective role of SOD in cells against hydrogen peroxide induced damage as the increas SOD activity will prevent the inactivation of cluster and release of Fe(II) to participate in the Fenton reaction

Question 44

Molecular mechanism of NO reactivity

Answer 44

NO reacts with oxygen, superoxide and transition metals, each of the products of these reaction can participate in further reactions with the thiol groups

Question 45

NO’s Interactions with metals

Answer 45

react directly with other radicals or one electron donors/acceptors such as the iron in heme

Question 46

NO can also inhibt the activity of enzymes

Answer 46

utilize the heme prosthetic group in catalysis - this is well exaple in the inhibition of cytochrome P450 enzymes

Question 47

the binding of NO to either Fe(II) to Fe(III) heme

Answer 47

attenuates oxygenase activity

Question 48

binding between the NO and heme iron induces

Answer 48

a conformational change that displaces iron out of the plane of the porphyrin ring and acitvates the enzyme guanylate cyclase catalyzes the conversion of guanosine-5-triphosphate to cyclic guanosine 3,5monophosphate results in relaxation of smooth muscle(vasodialation) -this mechanism may be responsible for the therapeutic effects of nitroso-vasodialtors

Question 49

mechanism for interaction between NO and the thiol groups of cysteinsin proteins

Answer 49

is not understood reaction probably involves formation of NO+ through oxidation of NO by transition metals or reaction of NO with O2

Question 50

Genotoxicity of NO: exposure to NO has been shown to cause

Answer 50

deamination of DNA & RNA

Question 51

peroxynitrite, formed by reaction between NO and superoxide radical

Answer 51

believed to play a major role in radical-induced cell damage since it’s a stable molecule for several weeks

Question 52

peroxynitrite can nitrate phenolic rings such as tyrosine residues in proteins

Answer 52

tyrosine phosphorylation, altered protein function, increased protein turnover due to enhanced proteolysis, initiation of autoimmune reactions to antigenic haptens

Question 53

peroxynitrite but not NO

Answer 53

can rapidly inactivate aconitase its activity can then be totally restored by incubation with tiols and ferrous ion indicating that oxidation cluster by peroxynitrite may play a role in enzyme inactivation

Question 54

peroxynitrite can either react with the sulfhydryl groups of proteins or become protonated ot form peroxynitrous acid which decays rapidly and gives rise to

Answer 54

hydroxyl radical and ntirogen dioxide these radicals will then cause protein oxidation and lipid peroxidation