Short-term ammonium inhibition of nitrate uptake byAzotobacter chroococcum

✍ Scribed by Elisa Revilla; Francisco J. Cejudo; Antonio Llobell; Antonio Paneque

• Publisher: Springer
• Year: 1986
• Tongue: English
• Weight: 470 KB
• Volume: 144
• Category: Article
• ISSN: 0302-8933
• DOI: 10.1007/bf00410944

✦ Synopsis

Addition of NH4CI at low concentrations to

Azotobacter chroococcum cells caused an immediate cessation of nitrate uptake activity, which was restored when the added NH + was exhausted from the medium or by adding an NH + assimilation inhibitor, L-methionine-DL-sulfoximine (MSX) or L-methionine sulfone (MSF). In the presence of such inhibitors the newly-reduced nitrate was released into the medium as NH,~. When the artificial electron donor system ascorbate/N-methylphenazinium methylsulfate (PMS), which is a respiratory substrate that was known to support nitrate uptake by A. chroococeum while inhibiting glutamine synthetase activity, was the energy source, externally added NH + had no effect on nitrate uptake. It is concluded that, in A. chroocoecum cells, NH + must be assimilated to exert its short-term inhibitory effect on nitrate uptake. A similar proposal was previously made to explain the short-term ammonium inhibition of N2 fixation in this bacterium.