Transport of amino acids and ammonium in mycelium of Agaricus bisporus.
Mycelium of Agaricus bisporus took up methylamine (MA), glutamate, glutamine and arginine by high-affinity transport systems following Michaelis-Menten kinetics. The activities of these systems were influenced by the nitrogen source used for mycelial growth. Moreover, MA, glutamate and glutamine uptakes were derepressed by nitrogen starvation, whereas arginine uptake was repressed. The two ammonium-specific transport systems with different affinities and capacities were inhibited by NH(+)(4), with a K(i) of 3.7 microM for the high-velocity system. The K(m) values for glutamate, glutamine and arginine transport were 124, 151 and 32 microM, respectively. Inhibition of arginine uptake by lysine and histidine showed that they are competitive inhibitors. MA, glutamate and glutamine uptake was inversely proportional to the intracellular NH(+)(4) concentration. Moreover, increase of the intracellular NH(+)(4) level caused by PPT (DL-phosphinotricin) resulted in an immediate cessation of MA, glutamine and glutamate uptake. It seems that the intracellular NH(+)(4) concentration regulates its own influx by feedback-inhibition of the uptake system and probably also its efflux which becomes apparent when mycelium is grown on protein. Addition of extracellular NH(+)(4) did not inhibit glutamine uptake, suggesting that NH(+)(4) and glutamine are equally preferred nitrogen sources. The physiological importance of these uptake systems for the utilization of nitrogen compounds by A. bisporus is discussed.
Kersten
M A
MA
Department of Microbiology and Evolutionary Biology, Faculty of Science, University of Nijmegen, Toernooiveld 1, NL-6525 ED, Nijmegen, The Netherlands. miniquek@sci.kun.nl
Arninkhof
M J
MJ
Op den Camp
H J
HJ
Van Griensven
L J
LJ
van der Drift
C
C
D000364:Agaricus / Q000254:growth & development / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D001120:Arginine / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D003470:Culture Media; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006639:Histidine / Q000494:pharmacology; D007700:Kinetics; D008239:Lysine / Q000494:pharmacology; D008744:Methylamines / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism* / Q000494:pharmacology
D000596:Amino Acids; D002250:Carbon Radioisotopes; D003470:Culture Media; D008744:Methylamines; D000644:Quaternary Ammonium Compounds; D005973:Glutamine; D018698:Glutamic Acid; D006639:Histidine; D001120:Arginine; C027451:methylamine; D008239:Lysine