Pro-oxidant Activities
Further information: Pro-oxidantAntioxidants that are reducing agents can also act as pro-oxidants. For example, vitamin C has antioxidant activity when it reduces oxidizing substances such as hydrogen peroxide, however, it will also reduce metal ions that generate free radicals through the Fenton reaction.
- 2 Fe3+ + Ascorbate → 2 Fe2+ + Dehydroascorbate
- 2 Fe2+ + 2 H2O2 → 2 Fe3+ + 2 OH· + 2 OH−
The relative importance of the antioxidant and pro-oxidant activities of antioxidants are an area of current research, but vitamin C, which exerts its effects as a vitamin by oxidizing polypeptides, appears to have a mostly antioxidant action in the human body. However, less data is available for other dietary antioxidants, such as vitamin E, or the polyphenols. Likewise, the pathogenesis of diseases involving hyperuricemia likely involve uric acid's direct and indirect pro-oxidant properties.
That is, paradoxically, agents which are normally considered antioxidants can act as conditional pro-oxidants and actually increase oxidative stress. Besides ascorbate, medically important conditional pro-oxidants include uric acid and sulfhydryl amino acids such as homocysteine. Typically, this involves some transition-series metal such as copper or iron as catalyst. The potential role of the pro-oxidant role of uric acid in (e.g.) atherosclerosis and ischemic stroke is considered above. Another example is the postulated role of homocysteine in atherosclerosis.
Read more about this topic: Evolution Of Dietary Antioxidants
Famous quotes containing the word activities:
“Both gossip and joking are intrinsically valuable activities. Both are essentially social activities that strengthen interpersonal bonds—we do not tell jokes and gossip to ourselves. As popular activities that evade social restrictions, they often refer to topics that are inaccessible to serious public discussion. Gossip and joking often appear together: when we gossip we usually tell jokes and when we are joking we often gossip as well.”
—Aaron Ben-Ze’Ev, Israeli philosopher. “The Vindication of Gossip,” Good Gossip, University Press of Kansas (1994)