AmtB-mediated NH3 transport in prokaryotes must be active and as a consequence regulation of transport by GlnK is mandatory to limit futile cycling of NH4(+)/NH3.
The nature of the ammonium import into prokaryotes has been controversial. A systems biological approach makes us hypothesize that AmtB-mediated import must be active for intracellular NH(4)(+) concentrations to sustain growth. Revisiting experimental evidence, we find the permeability assays reporting passive NH(3) import inconclusive. As an inevitable consequence of the proposed NH(4)(+) transport, outward permeation of NH(3) constitutes a futile cycle. We hypothesize that the regulatory protein GlnK is required to fine-tune the active transport of ammonium in order to limit futile cycling whilst enabling an intracellular ammonium level sufficient for the cell's nitrogen requirements.
Department of Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, The Netherlands. fred.boogerd@falw.vu.nl
Fred C
FC
Boogerd
Hongwu
H
Ma
Frank J
FJ
Bruggeman
Wally C
WC
van Heeswijk
Rodolfo
R
García-Contreras
Douwe
D
Molenaar
Klaas
K
Krab
Hans V
HV
Westerhoff
D000641:Ammonia / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000502:physiology*; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D009713:Nucleotidyltransferases / Q000502:physiology*; D051922:PII Nitrogen Regulatory Proteins / Q000502:physiology*; D011387:Prokaryotic Cells / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D015219:Substrate Cycling / Q000502:physiology
C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds; D000641:Ammonia; C497878:glnK protein, E coli; D009713:Nucleotidyltransferases