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Catalytic Metals, Ascorbate and Free Radicals: Combinations to Avoid
Garry R. Buettner and Beth Anne Jurkiewicz
Vol. 145, No. 5 (May, 1996), pp. 532-541
Published by: Radiation Research Society
Stable URL: http://www.jstor.org/stable/3579271
Page Count: 10
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Trace levels of transition metals can participate in the metal-catalyzed Haber-Weiss reaction (superoxide-driven Fenton reaction) as well as catalyze the oxidization of ascorbate. Generally ascorbate is thought of as an excellent reducing agent; it is able to serve as a donor antioxidant in free radical-mediated oxidative processes. However, as a reducing agent it is also able to reduce redox-active metals such as copper and iron, thereby increasing the pro-oxidant chemistry of these metals. Thus ascorbate can serve as both a pro-oxidant and an antioxidant. In general, at low ascorbate concentrations, ascorbate is prone to be a pro-oxidant, and at high concentrations, it will tend to be an antioxidant. Hence there is a crossover effect. We propose that the "position" of this crossover effect is a function of the catalytic metal concentration. In this presentation, we discuss: (1) the role of catalytic metals in free radical-mediated oxidations; (2) ascorbate as both a pro-oxidant and an antioxidant; (3) catalytic metal catalysis of ascorbate oxidation; (4) use of ascorbate to determine adventitious catalytic metal concentrations; (5) use of ascorbate radical as a marker of oxidative stress; and (6) use of ascorbate and iron as free radical pro-oxidants in photodynamic therapy of cancer.
Radiation Research © 1996 Radiation Research Society