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Ammonium regulation in Aspergillus nidulans.
Journal of Bacteriology
|June 1, 1973
Summary
This study investigates ammonium regulation in Aspergillus nidulans, revealing that nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase (NADP-GDH) plays a dual role in controlling nutrient uptake based on extracellular and intracellular ammonium levels.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Ammonium is a crucial nutrient for microbial growth.
- Understanding ammonium assimilation and regulation is vital for microbial physiology.
Purpose of the Study:
- To elucidate the mechanisms of ammonium regulation in Aspergillus nidulans.
- To characterize ammonium uptake and enzyme activities in wild-type and mutant strains.
Main Methods:
- Measurement of l-glutamate, thiourea, and methylammonium uptake in wild-type and mutant Aspergillus nidulans cells.
- Assay of nitrate reductase and hypoxanthine dehydrogenase activities.
- Analysis of ammonium-derepressed mutants (meaA8, meaB6, DER3, amrA1, xprD1, gdhA1).
Main Results:
- Extracellular ammonium concentration dictates l-glutamate uptake, thiourea uptake, nitrate reductase, and hypoxanthine dehydrogenase activity.
- Intracellular ammonium concentration determines methylammonium uptake levels.
- gdhA mutants exhibit a lack of NADP-GDH activity and are derepressed for both external and internal ammonium.
Conclusions:
- A model for ammonium regulation in A. nidulans is proposed involving NADP-GDH.
- NADP-GDH complexes with extracellular ammonium to regulate nutrient uptake and enzyme activity.
- NADP-GDH also complexes with intracellular ammonium to control methylammonium uptake.