Nitrogen assimilating enzymes in the white button mushroom Agaricus bisporus

Abstract

Agaricus bisporus has the enzymic potential to assimilate ammonia by the activities of glutamine synthetase (EC 6.3.1 .2), NAD-dependent glutamate dehydrogenase (EC 1.4.1.2) and NADP-dependent glutamate dehydrogenase (EC 1.4.1.4). It also contains glutamate synthase (EC 1.4.7.1) and a number of transaminating activities like glutamate-oxaloacetate transaminase (EC 2.6.1. l), glutamate-pyruvate transaminase (EC 2.6.1 .2) and alanine-glyoxylate transaminase (EC 2.6.1.44). A. bisporus showed good growth in a defined buffered medium on glucose as a carbon source and a number of organic nitrogen compounds or ammonia as a nitrogen source. No growth was observed using nitrate as a nitrogen source. A. bisporus was not able to use organic nitrogen containing substances as a sole nitrogen and carbon source. Specific activities of the ammonia assimilating enzymes showed some variation when mycelia were cultivated on different nitrogen sources. Highest specific activities for glutamine synthetase, NAD-dependent glutamate dehydrogenase and NADP-dependent glutamate dehydrogenase were found when mycelia were grown on glutamate as a nitrogen source. Lowest values were found when the mycelia were grown on ammonia or glutamine. The specific activities of the ammonia assimilating enzymes showed no variation during maturation of the sporophores.

Purification and Characterization of the NAD-Dependent Glutamate Dehydrogenase in the Ectomycorrhizal FungusLaccaria bicolor(Maire) Orton

“…After the last step of purification, the enzyme was extremely unstable, even in the presence of several protectants such as glycerol, dithiotrethol, or mercaptoethanol at high concentrations. This is in agreement with the high thermolability of this enzyme already reported for a number of basidiomycete fungi including A. bisporus (Baars et al, 1994) and Pleurotus ostreatus . Similar instability of the enzyme was also found in lower fungi.…”

“…However, similar K m values for ammonium have already been reported in Dictyostelium discoideum (Pamula and Wheldrake, 1991) and in A. klebsiana (Yang and Lé John, 1994). However, lower K m values were found in P. ostreatus for ammonium and glutamate (3.3 and 0.18 mM, respectively) and in A. bisporus for ammonium (6.5 mM) (Baars et al, 1994).…”

“…However, Baars et al (1994) partially purified the enzyme in Agaricus bisporus, but its rather high instability did not allow an extensive characterization. This instability is likely to have been an obstacle in the purification of the NAD-GDH of Basidiomycetes and no detailed information on the pure enzyme is available from ectomycorrhizal fungi.…”

In Vitro Release by Aspergillus fumigatus of Galactofuranose Antigens, 1,3-β- d -Glucan, and DNA, Surrogate Markers Used for Diagnosis of Invasive Aspergillosis

“…release of a proton from the cell, as shown for other fungi (1,17). This study shows that the release of GM and other galf antigens by A. fumigatus during the logarithmic growth phase corresponds with the increase in fungal biomass and the glucose concentration used.…”

Expression of the urease gene of Agaricus bisporus: a tool for studying fruit body formation and post-harvest development

“…No influence on the ammonia formation was found after addition of ATP to the urease reaction (unpublished data). Urea was shown to be a good nitrogen source for mycelial growth of A. bisporus (Baars et al 1994), and urease activity was demonstrated in fruit bodies (de Windt et al 2002). Besides urease, evidence for the presence of a urease inhibitor in cell-free extracts has been presented (Reinbothe et al 1967;de Windt et al 2002).…”