INTERACTIONS OF ASCORBATE AND CHELATED IRON IN A METHYLVIOLOGEN-MEDIATED MEHLER REACTION |
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| Authors: | Brad L Upham Leland S Jahnke Joyce G Foster |
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| Institution: | United States Department of Agriculture, Agricultural Research Service, Appalachian Soil &Water Conservation Research Laboratory, P.O. Box 867, Beckley, WV 25802-0867. USA;Biodynamics Institute, 711 Choppin Hall, Louisiana State University, Baton Rouge, LA 70803, USA;Department of Botany and Plant Pathology, University of New Hampshire, Durham, NH 03824, USA |
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| Abstract: | Abstract— –In the light, isolated spinach thylakoids consumed O2 in the presence of methylviologen, and ascorbate was found to interact with this reaction in various ways. Chelating-resin was used to remove metal impurities from the assay medium. Ascorbate diminished the H202 pool in resin-untreated solutions, while in resin-treated solutions ascorbate had no effect on H2O2 concentrations. A Fenton catalyst (Fe-EDTA) increased O2 uptake in the presence of ascorbate and decreased the amount of O2 recovered by catalase. Ascorbate tripled the rate of the methylviologen-mediated Mehler reaction, and the O2 consumed was liberated to 50% of its original concentration by catalase. Superoxide dismutase reversed the effects of ascorbate on the Mehler reaction rates. These results indicate that ascorbate can stimulate Mehler reactions indirectly by promoting a Fenton-type reaction as well as stimulating Mehler reactions directly by reducing 2O2- to 2H2O2. The promotion of a Fenton-type reaction by ascorbate appears to be the cause of H2O2 depletion in resin-untreated solutions. |
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