Oxidative Stress


Respiring organisms derive multiple benefits from molecular oxygen. However, some fraction of the oxygen used is unavoidably converted into dangerously reactive substances such as the superoxide radical (O2āˆ’), hydrogen peroxide (H2O2) and the hydroxyl radical (HO). These intermediates of oxygen reduction to water threaten the integrity of diverse biological molecules and hence the life of cells and organisms. The seeming comfort of aerobes in the presence of oxygen is due to their content of multilayered defences against these reactive metabolites of oxygen. There are superoxide dismutases that eliminate O2āˆ’ by efficiently dismuting it to oxygen and H2O2. There are catalases that eliminate H2O2 by dismuting it into water plus oxygen and there are also peroxidases that eliminate H2O2 and organic peroxides by reducing them to H2O and to alcohols, respectively. Removing O2āˆ’ and H2O2 prevents the formation of HO. However, no defence is perfect, so backing up these frontline defences that in large measure prevent oxidative damage, are others that repair the damage caused by the reactive derivatives of oxygen and, when that is not possible, eliminate the damaged molecules and replace them with newly synthesised ones.

Key Concepts:

  • The spin restriction facing oxygen reduction that favours the univalent pathway of oxygen reduction.

  • Superoxide, hydrogen peroxide and hydroxyl radical are intermediates on the univalent pathway.

  • These intermediates are reactive and can cause damage.

  • Defences are essential and have been evolved.

  • Superoxide dismutases protect against superoxide by converting it into hydrogen peroxide plus oxygen.

  • There are superoxide dismutases that contain copper plus zinc, manganese, iron or nickel at their active sites.

  • Catalases protect against hydrogen peroxide by converting it into oxygen plus water.

  • There are catalases with haem iron at the active site and others with manganese.

  • Peroxidases protect against hydrogen peroxide and against organic peroxides by reducing them to water and to alcohols, respectively.

  • Removing both superoxide and hydrogen peroxide prevents the formation of hydroxyl radical.

  • Oxidative stress contributes to multiple pathologies and to normal aging.

Keywords: superoxide dismutases; catalases; peroxidases; superoxide; hydrogen peroxide

Figure 1.

Why molecular oxygen has difficulty in accepting a pair of electrons.



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Fridovich, Irwin(Apr 2014) Oxidative Stress. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001376.pub3]