Ascorbate free radical as a marker of oxidative stress: an EPR study.

The ascorbate free radical (A.-) is a resonance-stabilized tricarbonyl species that is readily formed from the one-electron oxidation of ascorbate, AH-. Because of the low reduction potential of the A.-/AH- couple, Eo' = +282 mV, nearly every oxidizing radical that can arise in a biological system will bring about the one-electron oxidation of AH-, forming A.-. Thus, the steady-state concentration of A.- can be used as a measure of oxidative stress in chemical, biochemical, and biological systems. In this article, we discuss the energetics of ascorbate free radical reactions and demonstrate that the A.- electron paramagnetic resonance (EPR) signal intensity can serve as a marker for the degree of oxidative stress occurring in a system.