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GSE Chart of Reactive Oxygen Species (ROS)

Chart of ROS and their Metabolites in the Body

O2-and H2O2 - are primary reactive metabolites of oxygen

OH , LOO•, LO• - are produced by secondary reactions of the primary metabolites.

O2- is far less damaging than H2O2, which penetrates membranes andcan be transformed to OH, HOCl, 1O2*

Oxygen 3 O2


How ROS is Formed from Oxygen

Major Source (s) in Body

Products Generated

Superoxide RADICAL O2-

MildlyReactive Can not easily get into cells

3O2 is reduced by addition of 1 electron to outer shells

Electron leakage from mitochondrial Electron Transfer Chain:

3 O2 +e- O2-

Phagocytic respiratory burst (uses NADPH-dependent Oxidase):

NADPH +2O2 NADP + O2-+ H2O2

Phagocytes also produce:


Dismutation of O2-

O2- + O2- + 2H+ H2O2 + 1O2

Haber-Weiss Reaction - As reductant of free transition metals:

E.g. iron-catalyzed

(1) O2- + Fe3+ 3 O2 + Fe2+

(2) Fe2+ + H2O2 Fe3+ + OH+OH—





Passes easily into cells (because it is neutrally charged)

3 O2 is reduced by addition of 2 e's to outer shells

Dismutation of O2-

O2- + O2- + 2H+ H2O2 + 1O2*

Haber-Weiss Reaction (2) / Fenton Reaction - Main source ofOH in presence of free transition metals:

E.g. Iron-catalyzed

(2) H2O2+Fe2+ OH+ OH—+Fe3+

Production of HOCl by neutrophils:

H2O2 +Cl- HOCl +OH—

1O2* With hypochlorite or peroxynitrite

H2O2 + ClGAS 1O2*+ClGAS +H2O


Most potent biological oxidant

By reduction of H2O2 (i.e. by addition of 1 e-)

Haber-Weiss Reaction: O2- and H2O2 in the presence of freetransition metals produce MOST OH: E.g. Iron-catalyzed

(1) O2- + Fe3+ 3 O2 + Fe2+

(2) Fe2+ + H2O2 Fe3++ OH+OH—

Normally, most iron confined in RBCs

O3and H2O2

2 O3 +H2O2 OH +3 O2


Radiobiological damage

Singlet oxygen





Lowest excited state of oxygen

Passes easily into cells (because it is neutrally charged)

TherapiesEnergy input (radiation)

to 3 O2

Sensitizer with light and oxygen.(Basis of PDT for cancer)

“Excited”electron spin flips + jumps to next orbital

3 O2 +Energy 1O2*

Chlorophyll (in plants), retinal, flavins, dyes (Bengal rose, methylene blue), natural pigment (porphyrins)

Sens →Sens* Sens + 1O2*


Photosynthesis may occur in skin cells

Transfer the energy to a new molecule - thereby acting as a catalyst for free radical formation.

Reactions with substrate molecules - leading to the formation of a new free radical by oxidation.

(Olefins, dienes, sulphides, aromatics, hetero-aromatics, terpenes, steroids, fatty acids, flavones, tetracyclines, vitamines, amino acids, proteins, nucleic acids, blood and bile pigments, and synthetic polymers)

(1) Ene reaction – H abstraction/O2 addition

Lipid peroxidation:

RH+ 1O2*


Unsaturated lipid Hydroperoxide

(2) Cycloaddition –

Typically results in:


(3)Oxygenation - unfinished

1O2* reacts with ascorbate, producing H2O2


catalyzed by


/lipooxigenasesor myeloperoxidase (MPO) - in neutrophils, monocytes, new macrophages.


H2O2w/hypochlorite or peroxynitrite

H2O2 + ClGAS 1O2* +ClGAS +H2O

HOCl with O2- (MPO-dependent):

HOCl + O2- Cl- + OH + 1O2*

HOCl with H2O2:

HOCl + H2O2 HCl + H2O + 1O2*

Dismutation of O2- or ROO:

O2- + O2- + 2H+ H2O2 + 1O2*

(Non-catalyzed, rate pH-dependent)

O2- + O2- + 2H+ H2O2 + 3O2

(Enzymatically w/SOD very fast reaction)

ROO + ROO + 2H+ RO + 1O2*


Respiratory burst of phagocytes; By-product of metabolism

Thermo- decomposition of dioxetanes

Phosphite ozonides:

(RO)3PO3 (RO)3PO + 1O2* Endoperoxides:

E.g. 9,10-diphenylanthracene peroxide (DAP)

Hydroperoxides (ROOH)/ Endoperoxides

React with some metal ions.

Involves breaking C=C bonds E.g. in carotene, chlorophyll, polyunsaturated fatty acids (PUFAs)

Produce Peroxyl ROO

/Alkoxyl Radicals RO

Vital for killer action



O2- as intermediate to OH;

Peroxide anionO2 2-;

O3 oxidizes/ionizes organic molecules(saturated hydrocarbons, amines, sulfhydryl groups and aromatic compounds) to chiefly aldehydes, ketones, acids or alcohols.

O3 will oxidize metals (except gold, platinum, and iridium) to metal oxides (much easier to remove) –

2Cu2++2H++ O3 2 Cu3++ H2O+O2

O3 changes oxides into peroxides:

SO2 + O3 SO3 + O2

O3 converts cyanides into cyanates

(1000 X less toxic than cyanide):

CN- + O3 CNO- + O2

O3 1O2* + O1*

Excited singlet oxygen MOLECULE


Excited oxygen ATOM O1*

Chlorine Dioxide

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