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BIOENERGETICS AND PHOTOSYNTHESIS

Three Maize Leaf Ferredoxin:NADPH Oxidoreductases Vary in Subchloroplast Location, Expression, and Interaction with Ferredoxin^1,[w]

Institute for Protein Research, Osaka University, Suita, Osaka 565–0871, Japan (S.O., G.T.H., Y.S., T.T., T.H.); Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-Ku, Tokyo 153–8902, Japan (G.K.); and Unité de Nutrition Azotée des Plantes, Institut National de la Recherche Agronomique, 78026 Versailles cedex, France (A.S.)

In higher plants, ferredoxin (Fd):NADPH oxidoreductase (FNR) catalyzes reduction of NADP⁺ in the final step of linear photosynthetic electron transport and is also implicated in cyclic electron flow. We have identified three leaf FNR isoenzymes (LFNR1, LFNR2, and LFNR3) in maize (Zea mays) chloroplasts at approximately equivalent concentrations. Fractionation of chloroplasts showed that, while LFNR3 is an exclusively soluble enzyme, LFNR1 is only found at the thylakoid membrane and LFNR2 has a dual location. LFNR1 and LFNR2 were found to associate with the cytochrome b₆f complex following its partial purification. We cloned LFNR3 and produced all three isoenzymes as stable, soluble proteins. Measurement of Fd reduction ability showed no significant differences between these recombinant enzymes. Column chromatography revealed variation between the interaction mechanisms of LFNR1 and LFNR2 with Fd, as detected by differential dependence on specific intermolecular salt bridges and variable sensitivity of interactions to changes in pH. A comparison of LFNR transcripts in leaves of plants grown on variable nitrogen regimes revealed that LFNR1 and LFNR2 transcripts are relatively more abundant under conditions of high demand for NADPH. These results are discussed in terms of the functional differentiation of maize LFNR isoenzymes.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Toshiharu Hase (enzyme{at}protein.osaka-u.ac.jp).

^[w] The online version of this article contains Web-only data.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070813.

^* Corresponding author; e-mail enzyme{at}protein.osaka-u.ac.jp; fax 81–6–6879–8613.

Received August 31, 2005; returned for revision August 31, 2005; accepted September 12, 2005.

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