Summary auto-generated
This 1994 study investigated the nitrogen assimilation enzymes in Agaricus bisporus (white button mushroom) mycelium and sporophores. Researchers demonstrated the presence of multiple ammonia-assimilating enzymes: glutamine synthetase (GS), NAD-dependent glutamate dehydrogenase (NAD-GDH), NADP-dependent glutamate dehydrogenase (NADP-GDH), and glutamate synthase (GOGAT), along with transaminating activities. The mushroom showed good growth on glucose with organic nitrogen sources (amino acids, urea, allantoin) or ammonia as the sole nitrogen source, but could not use nitrate or organic nitrogen compounds as both carbon and nitrogen sources simultaneously. Enzyme specific activities varied significantly depending on the nitrogen source used for cultivation, with highest activities for GDH and GS enzymes observed when mycelia were grown on glutamate. Notably, enzyme activity levels remained relatively constant during sporophore maturation across different developmental stages. These findings clarify the enzymatic pathways supporting ammonia assimilation in this economically important fungus.
Key findings
- Agaricus bisporus possesses functional ammonia assimilating enzymes including NAD-GDH, NADP-GDH, GS, and GOGAT that enable glutamate and glutamine biosynthesis
- The mushroom exhibits differential growth on various organic nitrogen sources (amino acids, urea, allantoin) and ammonia, but cannot use nitrate or amino acids as sole carbon-nitrogen sources
- Enzyme-specific activities show significant variation based on nitrogen source, with glutamate-grown mycelia displaying highest GDH and GS activities
- Ammonia assimilating enzyme levels remain constant throughout sporophore development stages, suggesting stable nitrogen metabolism during fruiting body maturation
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Abstract
Agaricus bisporus has the enzymic potential to assimilate ammonia by the activities of glutamine synthetase (EC 6.3.1.2), NADp-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 2.6.1.1), 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.