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 upt...

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Bibliographic Details
Published in:	Biochimica et biophysica acta Vol. 1428; no. 2; pp. 260 - 272
Main Authors:	Kersten, Monique A.S.H, Arninkhof, Michel J.C, Op den Camp, Huub J.M, Van Griensven, Leo J.L.D, van der Drift, Chris
Format:	Journal Article
Language:	English
Published:	Netherlands Elsevier B.V 05-08-1999
Subjects:	Agaricus - growth & development Agaricus - metabolism Agaricus bisporus Amino Acids - metabolism Arginine Arginine - metabolism Biological Transport - drug effects Carbon Radioisotopes Culture Media Glutamate Glutamic Acid - metabolism Glutamine Glutamine - metabolism Histidine - pharmacology Kinetics Lysine - pharmacology Methylamine Methylamines - metabolism Quaternary Ammonium Compounds - metabolism Quaternary Ammonium Compounds - pharmacology Transport Agaricus bisporus AAM, amino acid mixture MA, methylamine AZS, azaserine Glutamate CE, compost extract MES, 2-( N-morpholino)ethanesulfonic acid NAD-GDH, NAD-dependent glutamate dehydrogenase Methylamine GS, glutamine synthetase NADP-GDH, NADP-dependent glutamate dehydrogenase Arginine MSX, l-methionine- S-sulfoximine CEA, compost extract agar GOGAT, glutamate synthase DNP, 2,4-dinitrophenol Transport PPT, dl-phosphinotricin Glutamine
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Summary:	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 μM for the high-velocity system. The K m values for glutamate, glutamine and arginine transport were 124, 151 and 32 μM, 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.
ISSN:	0304-4165 0006-3002 1872-8006
DOI:	10.1016/S0304-4165(99)00093-8