Chromium uptake,retention and reduction in photosynthetic <Emphasis Type="Italic">Euglena gracilis</Emphasis> |
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Authors: | J D García-García J S Rodríguez-Zavala R Jasso-Chávez D Mendoza-Cozatl Rafael Moreno-Sánchez |
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Institution: | (1) Departamento de Bioquímica, Instituto Nacional de Cardiología, Juan Badiano # 1, Sección XVI, Tlalpan, 14080 Mexico D.F., Mexico |
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Abstract: | Photosynthetic Euglena gracilis grown with different K2CrO4 concentrations was analyzed for its ability to take up, retain and reduce Cr(VI). For comparison, cells were also exposed
to CrCl3. Cellular Cr(VI) uptake at pH 7.2 showed a hyperbolic saturation pattern with K
m of 1.1 mM, V
m of 16 nmol (h × 107 cells)−1, and K
i sulfate of 0.4 mM. Kinetic parameters for sulfate uptake were similar, K
m = 0.83 mM, V
m = 15.9 nmol (h × 107cells)−1 and K
i chromate = 0.3 mM. The capacity to accumulate chromium depended on the ionic species, external concentration and pH of the incubation
medium. Cr(VI) or Cr(III) accumulation was negligible in the acidic (pH 3.5) culture medium, in which Cr(VI) was abiotically
reduced to Cr(III). At pH 7.2 Cr(VI) was fully stable and high accumulation (>170 nmol/1 × 107 cells at 1 mM K2CrO4) was achieved; surprisingly, Cr(III) accumulation was also significant (>35 nmol/1 × 107 cells at 1 mM CrCl3). Cr(VI) was reduced by cells at pH 7.2, suggesting the presence of an external reductive activity. Cr(VI) induced an increased
cysteine and glutathione content, but not in phytochelatins suggesting that chromium accumulation was mediated by monothiol
compounds. |
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Keywords: | Chromium uptake Sulfate uptake Chromium accumulation Chromium reduction Cysteine Glutathione |
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