Det er et paradoks i metabolismen til organismer. Selv om de fleste organismer på jorden trenger oksygen for å overleve, er oksygen et svært reaktivt molekyl som kan ødelegge organismer ved å produsere reaktive oksygenarter. Derfor er det etablert et komplekst nettverkssystem sammensatt av antioksidantmetabolitter og enzymer i organismen. Gjennom det synergistiske samarbeidet mellom antioksidantmetabolske mellomprodukter og produkter og enzymer, er viktige cellulære komponenter som DNA, protein og lipider beskyttet mot oksidativ skade. Antioksidantsystemet oppnår i utgangspunktet antioksidanteffekter på to måter, den ene er å forhindre produksjon av aktive oksygenstoffer, og den andre er å eliminere disse aktive stoffene før de skader viktige komponenter i cellen for å oppnå anti-oksidasjon . Effektiv. Imidlertid har disse reaktive oksygenartene også viktige cellulære funksjoner, for eksempel å fungere som redokssignalmolekyler i biokjemiske reaksjoner. Derfor er ikke antioksidantsystemets rolle i organismen å fjerne alle oksiderende stoffer fullstendig, men å holde disse stoffene på et passende nivå.
The reactive oxygen species produced in cells include hydrogen peroxide (H2O2), hypochlorous acid (HClO), free radicals such as hydroxyl radicals (·OH) and superoxide anions (O2). Hydroxyl radicals are particularly unstable and can react with most biomolecules quickly and without specificity. Such species are mainly produced by metal-catalyzed hydrogen peroxide reduction (such as Fenton reaction). These oxidants destroy cells by initiating chain reactions such as lipid peroxidation, or oxidizing DNA and proteins. If the damaged DNA is not repaired, it can cause mutations and induce cancer. Damage to the protein can inhibit the activity of the enzyme, and the protein will be denatured or degraded.
The human body needs to consume oxygen to generate reactive oxygen species in the process of energy production. In this process, several steps in the electron transport chain can produce by-product superoxide anions. It is particularly important that the coenzyme Q in complex III becomes a highly active free radical intermediate (Q·) during the reduction process. This unstable intermediate will cause electronic "leakage" (loss of electrons), and the "leaked" electrons will jump out of the normal electron transport chain and directly reduce oxygen molecules to produce superoxide anions. Peroxide can also be produced by the oxidation of reduced flavoproteins such as complex I. However, although these enzymes produce oxidants, it is not clear whether the electron transport chain is more important than other biochemical processes that can also produce peroxides. In the process of photosynthesis of plants, algae and cyanobacteria, especially under high irradiation intensity, reactive oxygen species are also produced, but carotenoids are used as photoprotective agents to absorb excessive strong light to protect cells. The algae and cyanobacteria contain A large amount of iodine and selenium can also offset the oxidative damage caused by high radiation intensity. Carotenoids, iodine and selenium act as antioxidants to avoid the production of reactive oxygen species by reacting with the over-reduced photosynthetic reaction center.
