Journal Article

Donation of Electrons to Plastoquinone by NAD(P)H Dehydrogenase and by Ferredoxin-Quinone Reductase in Spinach Chloroplasts

Tsuyoshi Endo, Hualing Mil, Toshiharu Shikanai and Kozi Asada

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 38, issue 11, pages 1272-1277
Published in print January 1997 | ISSN: 0032-0781
Published online January 1997 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029115
Donation of Electrons to Plastoquinone by NAD(P)H Dehydrogenase and by Ferredoxin-Quinone Reductase in Spinach Chloroplasts

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The reduction of plastoquinone by NADPH was detected as an increase in the dark level of Chi fluorescence in osmotically ruptured chloroplasts of spinach. This activity was observed only when the chloroplasts were ruptured in a medium containing a high concentration of MgCl2. The activity was suppressed by inhibitors of the respiratory NADH dehydrogenase (NDH) complex in mitochondria, capsaicin and amobarbital, suggesting that the activity was mediated by chloroplastic NDH complex. Antimycin A, an inhibitor of ferredoxin-quinone reductase (FQR), and the protonophore nigericin also inhibited the increase in Chi fluorescence by NADPH. By contrast, JV-ethylmaleimide (NEM), an inhibitor of ferredoxin-NADP+ reductase (FNR), did not suppress the fluorescence increase, showing that FNR is not involved in this reaction. When the osmotically ruptured chloroplasts were washed by centrifugation, a further addition of ferredoxin as well as NADPH was required for an increase in fluorescence. This ferredoxin-de-pendent activity also was suppressed by antimycin A, but only partly inhibited by capsaicin or amobarbital, suggesting that this is mediated mainly by FQR. These findings suggest that the NADPH-binding subunit of NDH complex is easily dissociated from the thylakoid membranes during the process of the washing the thylakoids by centrifugation.

Keywords: Antimycin A; Cyclic electron transport; Ferredoxin-NADP+ reductase (FNR, EC 1.6.7.1); Ferredoxin-quinone reductase (FQR); NAD(P)H dehydrogenase (NDH, EC 1.6.99.3); Spinacia oleracea (Spinach)

Journal Article.  0 words. 

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

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