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Soil Science Society of America Journal Abstract -

Stability Constants of Pseudobactin Complexes with Transition Metals


This article in SSSAJ

  1. Vol. 58 No. 2, p. 390-396
    Received: Apr 26, 1993

    * Corresponding author(s):
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  1. Yona Chen ,
  2. Edouard Jurkevitch,
  3. Eli Bar-Ness and
  4. Yitzhak Hadar
  1. Dep. of Soil and Water Sciences
    Dep. of Microbiology and Plant Pathology, Faculty of Agriculture, Hebrew Univ. of Jerusalem, Rehovot 76100, Israel



The stability constants of the fluorescent siderophore pseudobactin St3 (PSB3) produced by Pseudomonas putida strain 3 with Fe3, Cu2+, Mn2+, Zn2+, and Fe2+ were determined using fluorescence spectroscopy and potentiometric titrations. Stability constants for PSB3, with Fe3+, Fe2+, Mn2+, and Zn2+ were determined based on titration to saturation of a PSB3 ligand solution with either of the metals, then back-titrating the solution with an EDTA solution along with simultaneous measurements of fluorescence and visible spectra. A nonlinear curve fitting between the fluorescence intensity (Y) and the concentration (C) of the metal or EDTA was used for the determination of the concentrations of the free and complexed ligands. The overall stability constant (log KML) obtained for Fe3+ by this method was the same as that obtained by visible spectrosopy. The log KML. values obtained by fluorescence spectroscopy for Mn2+ and Zn2+ (17.5 and 19.4, respectively) were in good agreement with log KML values obtained by potentiometric titration (17.3 and 19.8, respectively). It was found that two chromatography bands obtained from PSB3 solutions isolated and purified from cultures grown under different conditions chelated Fe3+ with practically the same affinity. The log KML of PSB3 with Fe3+, Zn2+, Cu2+, Mn2+, and Fe2+ were calculated using the protonation constants determined by potentiometry (pKa1 = 11.28, pKa2 = 7.74, pKa3 = 5.35) and were found to be 29.6, 19.8, 22.3, 17.3, and 8.3, respectively.

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