Journal Article

The FAD-Enzyme Monodehydroascorbate Radical Reductase Mediates Photoproduction of Superoxide Radicals in Spinach Thylakoid Membranes

Chikahiro Miyake, Ulrich Schreiber, Henning Hormann, Satoshi Sano and Asada Kozi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 39, issue 8, pages 821-829
Published in print August 1998 | ISSN: 0032-0781
Published online August 1998 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029440
The FAD-Enzyme Monodehydroascorbate Radical Reductase Mediates Photoproduction of Superoxide Radicals in Spinach Thylakoid Membranes

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The photoreduction of dioxygen in spinach thylakoid membranes was enhanced about 10-fold by the FAD-enzyme monodehydroascorbate radical (MDA) reductase at 1 μM. The primary photoreduced product of dioxygen catalyzed by MDA reductase was the superoxide radical, as evidenced by the inhibition of photoreduction of Cyt c by superoxide dismutase. The apparent Km for dioxygen of the MDA reductase-dependent photoreduction of dioxygen was 100 μM, higher by one order of magnitude than that observed with thylakoid membranes only. Glutathione reductase, ferredoxin-NADP+ reductase, and glycolate oxidase also mediated the photoproduction of superoxide radicals in thylakoid membranes at rates similar to those with MDA reductase. Among these flavoenzymes, MDA reductase is the most likely mediator stimulating the photoreduction of dioxygen in chloroplasts; its function in the protection from photoinhibition under excess light is discussed.

Keywords: Active species of oxygen; Monodehydroascorbate radical; Monodehydroascorbate radical reductase (EC 1.6.5.4); Photosystem I; Superoxide radical; Thylakoid membranes

Journal Article.  0 words. 

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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