response to ammonium ion

Definition

Target type: biologicalprocess

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an ammonium stimulus. [GO_REF:0000071, GOC:TermGenie, PMID:23509267]

Response to ammonium ion is a critical biological process that enables organisms to adapt to fluctuating ammonia levels in their environment. It involves a complex network of cellular pathways and mechanisms aimed at sensing, transporting, assimilating, and detoxifying ammonium.

**Sensing and Transport:**

* Organisms employ various ammonium sensors to detect changes in ammonia concentration. These sensors can be membrane-bound proteins, such as AmtB in bacteria, or intracellular enzymes, like glutamine synthetase in plants.
* Once detected, ammonium is transported across cell membranes via specific transporters. These transporters can be active, requiring energy to move ammonium against its concentration gradient, or passive, facilitating movement down the concentration gradient.

**Assimilation:**

* The primary pathway for ammonium assimilation is the **glutamine synthetase/glutamate synthase (GS/GOGAT) pathway.** This pathway incorporates ammonium into glutamine, which then serves as a nitrogen donor for the synthesis of other amino acids.
* In this pathway, glutamine synthetase catalyzes the ATP-dependent reaction of ammonium with glutamate to form glutamine.
* Glutamate synthase then utilizes reducing equivalents (NADH or NADPH) to transfer the nitrogen from glutamine to α-ketoglutarate, generating glutamate.

**Detoxification:**

* Excess ammonium can be toxic to cells. To prevent accumulation, organisms employ detoxification mechanisms.
* In mammals, the liver plays a crucial role in ammonium detoxification through the **urea cycle.** This cycle converts ammonium into urea, which is excreted in urine.
* Plants and microbes often utilize **ammonium assimilation** or **ammonium volatilization** to remove excess ammonium.

**Regulation:**

* Response to ammonium ion is tightly regulated to maintain cellular homeostasis.
* Regulatory mechanisms include transcriptional and post-translational control of gene expression for key enzymes in ammonium metabolism, as well as feedback inhibition by the end products of ammonium assimilation.

**Ecological Significance:**

* Ammonium is an essential nutrient for all living organisms, playing a vital role in nitrogen fixation and the nitrogen cycle.
* Response to ammonium ion is crucial for the survival and growth of organisms in various environments, including soil, water, and the human gut.

**Overall, response to ammonium ion is a multifaceted biological process that is essential for the survival and growth of all living organisms. It involves a complex network of sensing, transport, assimilation, and detoxification pathways that are tightly regulated to maintain cellular homeostasis and ensure proper nitrogen utilization.**'
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Proteins (1)

Compounds (1)