Plant Physiol. Illumina
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Plant Physiology 82:904-908 (1986)
© 1986 American Society of Plant Biologists

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Articles

Kinetic Characterization of Nitrite Uptake and Reduction by Chlamydomonas reinhardtii1

Francisco Córdoba, Jacobo Cárdenas and Emilio Fernández

Departamento de Bioquímica, Facultad de Ciencias, Universidad de Córdoba, Córdoba 14071, Spain

Kinetics of nitrite uptake and reduction by Chlamydomonas reinhardtii cells growing phototrophically has been studied by means of progress curves and the Michaelis-Menten integrated equation. Both uptake and reduction processes exhibited hyperbolic saturation kinetics, the nitrite uptake system lacking a diffusion component. Nitrite uptake and reduction showed significant differences in Ks for nitrite at pH 7.5 (1.6 versus 20 micromolar, respectively), optimal pH, activation energy values, and sensitivity toward reagents of sulfhydryl groups. Ks values for nitrite uptake were halved in cells subjected to darkness or to nitrogen-starvation. Nitrate inhibited nitrite uptake by a partially competitive mechanism. The same inhibition pattern was found for nitrite uptake by C. reinhardtii mutant 305 cells incapable of nitrate assimilation. The results demonstrate that C. reinhardtii cells take up nitrite via a highly specific carrier, probably energy-dependent, kinetically responsive to environmental changes, distinguishable from the enzymic nitrite reduction and endowed with an active site for nitrite not usable for nitrate transport.

1 Supported by Comisión Asesora de Investigación Científica y Técnica (grant 1834-82).




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J. Rexach, B. Montero, E. Fernandez, and A. Galvan
Differential Regulation of the High Affinity Nitrite Transport Systems III and IV in Chlamydomonas reinhardtii
J. Biol. Chem., September 24, 1999; 274(39): 27801 - 27806.
[Abstract] [Full Text] [PDF]

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 J. Biol. Chem.Home page
A. Galván, A. Quesada, and E. Fernández
Nitrate and Nitrite Are Transported by Different Specific Transport Systems and by a Bispecific Transporter in Chlamydomonas reinhardtii
J. Biol. Chem., January 26, 1996; 271(4): 2088 - 2092.
[Abstract] [Full Text] [PDF]


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Copyright © 1986 by the American Society of Plant Biologists