| Popis: |
The chapter emphasizes on the thermodynamic, kinetic, and biochemical constraints that explain why the production of free radicals and peroxides and the cost of their elimination are inseparable from the aerobic life of cells. Toxic byproducts of oxygen do not only include electrophiles, such as H 2 O 2 , ROOH, HO 2 • , OH • , RO • , ROO • , aldehydes, and epoxides but also nucleophiles, such as O 2 • − , HO 2 − , and ferryl species. Both one-electron and two-electron transfers can be coupled to the production of free radicals and activated oxygen species in physiological conditions. Several activated oxygen species are interconvertible, and their cellular destiny relies on a dynamic set of reactions, many of which never reach a true state of equilibrium. While superoxide may be very toxic by itself, hydroperoxides—such as H 2 O 2 and ROOH—are immediate precursors of highly damaging free radicals. It is therefore important to realize that these three molecular species are normally produced by many physiological sources in the aerobic environment of mammalian cells and tissues. |
