Regulation of methylammonium/ammonium transport in the unicellular cyanobacterium Synechococcus R-2 (PCC 7942) |
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Authors: | Samy Boussiba Jane Gibson |
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Affiliation: | The Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel;Section of Biochemistry, Molecular and Cell Biology, Division of Biological Sciences, Cornell University, Ithaca, NY 14853, U.S.A. |
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Abstract: | The unicellular cyanobacterium Synechococcus R-2 (PCC 7942) took up 14CH3NH+3 at least 10 times faster after growth with NO?3 than with NH+4 as nitrogen source. When NH+4-grown cells were transferred to medium containing NO?3, the ability to accumulate 14CH3NH+3 required approximately 6 h for maximal expression. Chloramphenicol (50 μg · ml?1) completely prevented the rise in transport ability. Transport by nitrate-grown cells incubated in 2 mM NH4Cl or CH3NH3Cl, with or without NO?3, continued at high rates for 2–3 h, but fell to zero by about 5 h incubation in light. Methylammonium, or the γ-methyl glutamic amide derived from it, thus may also serve as a signal for repression; however, externally added glutamine stimulated rather than repressed 14CH3NH+3 transport. Changes in 14CH3NH+3 uptake rates brought about by NH+4 were confined to these slow effects, and to competition for entry into the cell. |
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Keywords: | Methylammonium transport Synechococcus R-2 (regulation) |
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