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Journal of Bacteriology, March 2009, p. 1472-1479, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01473-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Ferredoxin-NADP+ Reductase from Pseudomonas putida Functions as a Ferric Reductase{triangledown}

Jinki Yeom,1 Che Ok Jeon,2 Eugene L. Madsen,3 and Woojun Park1*

Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-075, Republic of Korea,1 Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea,2 Department of Microbiology, Cornell University, Ithaca, New York 14853-81013

Received 20 October 2008/ Accepted 19 December 2008

Pseudomonas putida harbors two ferredoxin-NADP+ reductases (Fprs) on its chromosome, and their functions remain largely unknown. Ferric reductase is structurally contained within the Fpr superfamily. Interestingly, ferric reductase is not annotated on the chromosome of P. putida. In an effort to elucidate the function of the Fpr as a ferric reductase, we used a variety of biochemical and physiological methods using the wild-type and mutant strains. In both the ferric reductase and flavin reductase assays, FprA and FprB preferentially used NADPH and NADH as electron donors, respectively. Two Fprs prefer a native ferric chelator to a synthetic ferric chelator and utilize free flavin mononucleotide (FMN) as an electron carrier. FprB has a higher kcat/Km value for reducing the ferric complex with free FMN. The growth rate of the fprB mutant was reduced more profoundly than that of the fprA mutant, the growth rate of which is also lower than the wild type in ferric iron-containing minimal media. Flavin reductase activity was diminished completely when the cell extracts of the fprB mutant plus NADH were utilized, but not the fprA mutant with NADPH. This indicates that other NADPH-dependent flavin reductases may exist. Interestingly, the structure of the NAD(P) region of FprB, but not of FprA, resembled the ferric reductase (Fre) of Escherichia coli in the homology modeling. This study demonstrates, for the first time, the functions of Fprs in P. putida as flavin and ferric reductases. Furthermore, our results indicated that FprB may perform a crucial role as a NADH-dependent ferric/flavin reductase under iron stress conditions.

* Corresponding author. Mailing address: Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-075. Phone: 82-2-3290-3067. Fax: 82-2-953-0737. E-mail: wpark{at}korea.ac.kr

{triangledown} Published ahead of print on 29 December 2008.

Journal of Bacteriology, March 2009, p. 1472-1479, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01473-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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