Ferrous-iron-dependent uptake of L-glutamate by a mesophilic, mixotrophic iron-oxidizing bacterium strain OKM-9.
Strain OKM-9 is a mesophilic, mixotrophic iron-oxidizing bacterium that absolutely requires ferrous iron as its energy source and L-amino acids (including L-glutamate) as carbon sources for growth. The properties of the L-glutamate transport system were studied with OKM-9 resting cells, plasma membranes, and actively reconstituted proteoliposomes. L-Glutamate uptake into resting cells was totally dependent on ferrous iron that was added to the reaction mixture. Potassium cyanide, an iron oxidase inhibitor, completely inhibited the activity at 1 mM. The optimum pH for Fe2+-dependent uptake activity of L-glutamate was 3.5-4.0. Uptake activity was dependent on the concentration of the L-glutamate. The Km and Vmax for L-glutamate were 0.4 mM and 11.3 nmol x min(-1) x mg(-1), respectively. L-Aspartate, D-aspartate, D-glutamate, and L-cysteine strongly inhibited L-glutamate uptake. L-Aspartate competitively inhibited the activity, and the apparent Ki for this amino acid was 75.9 microM. 2,4-Dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, gramicidin D, valinomycin, and monensin did not inhibit Fe2+-dependent L-glutamate uptake. The OKM-9 plasma membranes had approximately 40% of the iron-oxidizing activity of the resting cells and approximately 85% of the Fe2+-dependent uptake activity. The glutamate transport system was solubilized from the membranes with 1% n-octyl-beta-D-glucopyranoside and reconstituted into a lecithin liposome. The L-glutamate transport activity of the reconstituted proteoliposomes was 8-fold than that of the resting cells. The Fe2+-dependent L-glutamate uptake observed here seems to explain the mixotrophic nature of this strain, which absolutely requires Fe2+ oxidation when using amino acids as carbon sources.
Inoue
Takao
T
Division of Science and Technology for Energy Conversion, Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka, Okayama 700-8530, Japan.
Kamimura
Kazuo
K
Sugio
Tsuyoshi
T
D001419:Bacteria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D001693:Biological Transport, Active / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D005296:Ferrous Compounds / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism*; D010084:Oxidation-Reduction; D011510:Proteolipids
D001426:Bacterial Proteins; D003470:Culture Media; D005296:Ferrous Compounds; D011510:Proteolipids; C020485:proteoliposomes; D018698:Glutamic Acid