Multiplicity of ammonium uptake systems in Corynebacterium glutamicum: role of Amt and AmtB.
In Corynebacterium glutamicum, a Gram-positive soil bacterium widely used in the industrial production of amino acids, two genes encoding (putative) ammonium uptake carriers have been described. The isolation of amt was the first report of the sequence of a gene encoding a bacterial ammonium uptake system combined with the characterization of the corresponding protein. Recently, a second amt gene, amtB, with so far unknown function, was isolated. The isolation of this gene and the suggestion of a new concept for ammonium acquisition prompted the reinvestigation of ammonium transport in C. glutamicum. In this study it is shown that Amt mediates uptake of (methyl)ammonium into the cell with high affinity and strictly depending on the membrane potential. As shown by the determination of K:(m) at different pH values, ammonium/methylammonium, but not ammonia/methylamine, are substrates of Amt. AmtB exclusively accepts ammonium as a transport substrate. In addition, hints of another, until now unknown, low-affinity, ammonium-specific uptake system were found.
Meier-Wagner
J
J
Institut für Biochemie der Universität zu Köln, Zülpicher-Str. 47, D-50674 Köln, Germany.
Nolden
L
L
Jakoby
M
M
Siewe
R
R
Krämer
R
R
Burkovski
A
A
D001426:Bacterial Proteins; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D003352:Corynebacterium / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008744:Methylamines / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D014158:Transcription, Genetic; D014475:Uncoupling Agents / Q000378:metabolism
C098742:(methyl)ammonium uptake carrier, Corynebacterium; C111096:AmtB protein, E coli; D001426:Bacterial Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D008744:Methylamines; D000644:Quaternary Ammonium Compounds; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C027451:methylamine