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Chart of Reactive Oxygen Species (ROS)

Chart of ROS and their Metabolites in the Body

O2and 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 and  can be transformed to OH, HOCl,  1O2*

Oxygen 3 O2

A di-RADICAL

How ROS is Formed from Oxygen

Major Source (s) in Body

Products Generated

Superoxide RADICAL O2

Mildly  Reactive Can not easily get into cells

3 O2     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:

    OH    1O2*      NO*   ONOO⁻

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

 

H2O2

Poorly

Reactive

 NON-radical

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 of OH· 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

 

 

 

 

Hydroxyl RADICAL OH

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 free  transition 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

 

 

O3   and H2O2

2 O3 +   H2O2     OH +  3 O2   

Radiation

Radiobiological damage

 

 

 

 

 

 

 

Singlet oxygen

1O2*

Highly

Reactive

NON-radical

 

 
 

 

 

 


Lowest excited state of oxygen

 

Passes easily into cells (because it is neutrally charged)

 Therapies Energy 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*      

               uv         O2

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*  

                          ROOH

 Unsaturated lipid Hydroperoxide

 

(2) Cycloaddition –

Typically results in:

 1,2-dioxetane  or  Endoperoxide

 

(3)  Oxygenation - unfinished

 

 

 

1O2*      reacts with ascorbate, producing H2O2

Enzymatically

catalyzed by  

 peroxidases  

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

Or SOD

H2O2 w/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*      

Endogenously

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

 

Ozone  

O3

 

 

O2 as intermediate to OH;

 

Peroxide anion  O2 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  

1O2*

Excited  oxygen ATOM O1*

 

 

Chlorine Dioxide

 

 

 

AOX - ROS Related Links

ANTIOXIDANT / OXIDANT  BALANCE  Related Links

Health is a Balancing Act Between OXIDANTS and ANTIOXIDANTS 

-   A Powerful bioxidative tool

LIFE'S OXYGEN PARADOX

- Meet Dr. ROS Jeckyll

              and Mr. ROS Hyde

•   Dr. ROS Jeckyll

•   Mr. ROS Hyde

-   Where do Body’s ROS Come From?

 

 Ÿ•     ROS Chart

-   Antioxidants - Oxidant Damage Control

 

•    ENZYMATIC ANTIOXIDANTS

•    NON-ENZYMATIC ANTIOXIDANTS