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Journal of Bacteriology, April 1999, p. 2142-2147, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Iron Reductase for Magnetite Synthesis in the Magnetotactic Bacterium Magnetospirillum magnetotacticum

Yasushi Noguchi,1 Taketomo Fujiwara,2 Katsuhiko Yoshimatsu,2 and Yoshihiro Fukumori3,*

Department of Life Science, Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8501,1 Department of Biology, Faculty of Science, Shizuoka University, Shizuoka 422-8529,2 and Department of Biology, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192,3 Japan

Received 9 November 1998/Accepted 13 January 1999

Ferric iron reductase was purified from magnetotactic bacterium Magnetospirillum (formerly Aquaspirillum) magnetotacticum (ATCC 31632) to an electrophoretically homogeneous state. The enzyme was loosely bound on the cytoplasmic face of the cytoplasmic membrane and was found more frequently in magnetic cells than in nonmagnetic cells. The molecular mass of the purified enzyme was calculated upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be about 36 kDa, almost the same as that calibrated by gel filtration analysis. The enzyme required NADH and flavin mononucleotide (FMN) as optimal electron donor and cofactor, respectively, and the activity was strongly inhibited by Zn2+ acting as a partial mixed-type inhibitor. The Km values for NADH and FMN were 4.3 and 0.035 µM, respectively, and the Ki values for Zn2+ were 19.2 and 23.9 µM for NADH and FMN, respectively. When the bacterium was grown in the presence of ZnSO4, the magnetosome number in the cells and the ferric iron reductase activity declined in parallel with an increase in the ZnSO4 concentration of the medium, suggesting that the ferric iron reductase purified in the present study may participate in magnetite synthesis.

* Corresponding author. Mailing address: Department of Biology, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. Phone: 81-76-264-5719. Fax: 81-76-264-5918. E-mail: fukumor{at}kenroku.kanazawa-u.ac.jp.

Journal of Bacteriology, April 1999, p. 2142-2147, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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