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Volume 15 Part 1 Article 6
Year 2000
Title: The glutamine synthetase from the edible mushroom Agaricus bisporus
Authors: M.A.S.H. Kersten, Cvan der Drift, HJ.M.Op den Camp, J.J.P. Baars, L.J.L.D. Van Griensven, P.J. Schaap, Y. Müller, J. Visser and J.A.M. Leunissen

Abstract:

[¹⁵N]-NMR labeling studies showed that ammonium assimilation in Agaricus bisporus is catalyzed by glutamine synthetase (GS), This paper brings together available knowledge on the GS of A. bisporus. The enzyme was purified and a number of characteristics of this GS-II type enzyme were determined. The gene encoding GS (glnA) was isolated and a phylogenetic study of 23 GSII genes showed that the A. bisporus amino acid is highly homologous to the Saccharomyces cerevisiae GS sequence. GS from plants branched earlier from the eukaryotic lineage than the animals and fungi. Sequence comparisons showed conserved regions between the genes which can be correlated to catalytic and structural functions of the enzyme. The enzymic function seems to be highly conserved in both prokaryotes and eukaryotes. Regulation was studied using a specific antibody fraction directed against purified GS. GS protein and activity levels were measured in cell-free extracts of mycelium grown on different N sources. In mycelium grown on glutamine or ammonium, the biosynthetic GS activity is higher than the transferase activity. Moreover, the results show a conelation between GS biosynthetic activity, GS protein, and mRNA levels. Also, after addition of ammonium or glutamine to glutamate-utilizing cultures, transferase activity decreased more rapidly than biosynthetic activity and GS protein level. This suggests a conformational modification which only affects transferase activity.

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