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Photorespiration

C2 pathwayphotorespiratoryphotorespiratory reactions
Glutamine Synthetase uses ammonia produced by nitrate reduction, amino acid degradation, and photorespiration.
The assimilation of NH 3 occurs via the GS-GOGAT cycle, at a cost of one ATP and one NADPH.

Glutamine

Gln L -glutamineQ
Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:
Glutamine is synthesized by the enzyme glutamine synthetase from glutamate and ammonia.

Adenylylation

adenylationadenylatedadenylates
Tyr 397 of all 12 subunits can undergo adenylylation or deadenylylation by adenylyl transferase (AT), a bifunctional regulatory enzyme.
Similar to serine, threonine or tyrosine phosphorylation, AMPylation regulates the activity of some proteins, such as glutamine synthetase.

Methionine sulfoximine

Methionine sulfoximine (MSO): MSO is an inhibitor that binds to the glutamate site. Bound to GS, MSO is phosphorylated by ATP that results in an irreversible, non-covalent inhibition of GS. The S-isomer configuration is more inhibitory. Glutamate entry is blocked into the active site by a stabilization of the flexible loop in the active site by MSO.
Methionine sulfoximine (MSO) is an irreversible glutamine synthetase inhibitor.

Glufosinate

phosphinothricinglufosinate ammonium
Phosphinothricin (PPT, Glufosinate): Phosphinothricin is an inhibitor that binds to the glutamate site. Glufosinate is used as an herbicide. Glufosinate treated plants die due to a buildup of ammonia and a cessation of photosynthesis.
The compound irreversibly inhibits glutamine synthetase, an enzyme necessary for the production of glutamine and for ammonia detoxification, giving it antibacterial, antifungal and herbicidal properties.

NsiR4 small RNA

NsiR4
These inactivating factors are furthermore regulated by different Non-coding RNAs: The sRNA NsiR4 interacts with the 5'UTR of the mRNA of the GS inactivating factor IF7 ( gifA mRNA) and reduces its expression.
NsiR4 (nitrogen stress-induced RNA 4), former name SyR12, is a cyanobacterial non-coding RNA which plays role in the regulation of Glutamine synthetase (GS), a key enzyme in biological nitrogen assimilation.

GlnA RNA motif

glutamine riboswitchglutamine-binding riboswitch
In addition, expression of the GS inactivating factor IF17 is controlled by a glutamine-binding riboswitch.
The most prominent of these protein classes are ammonium transporters, the enzymes glutamine synthetase and glutamate synthase and P II protein, which itself regulates nitrogen metabolism.

Enzyme

enzymologyenzymesenzymatic
Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Metabolism

metabolicmetabolizedmetabolic pathways
Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Nitrogen

NN 2 dinitrogen
Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Glutamic acid

glutamateGluglutamate metabolism
Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Ammonia

NH 3 anhydrous ammonialiquid ammonia
Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Adenosine triphosphate

ATPadenosine triphosphate (ATP)adenosine 5'-triphosphate
Glutamate + ATP + NH 3 → Glutamine + ADP + phosphate

Adenosine diphosphate

ADPadenosine diphosphate (ADP)adenosine diphosphate sugars
Glutamate + ATP + NH 3 → Glutamine + ADP + phosphate

Amino acid

amino acidsresiduesresidue
Glutamine Synthetase uses ammonia produced by nitrate reduction, amino acid degradation, and photorespiration.

Metabolite

metabolitesactive metabolitebreakdown product
The amide group of glutamate is a nitrogen source for the synthesis of glutamine pathway metabolites.

Ammonium

ammonium saltammonium ionNH 4 +
Other reactions may take place via GS. Competition between ammonium ion and water, their binding affinities, and the concentration of ammonium ion, influences glutamine synthesis and glutamine hydrolysis.

Monomer

monomersmonomeric-mer
Bacterial GS are dodecamers with 12 active sites between each monomer.

Nucleotide

nucleotidesntdinucleotide
Each active site creates a ‘tunnel’ which is the site of three distinct substrate binding sites: nucleotide, ammonium ion, and amino acid.

Ion

cationanionions
The middle of the bifunnel contains two sites in which divalent cations bind (Mn+2 or Mg+2).

Hydrogen bond

hydrogen bondinghydrogen bondshydrogen-bonding
Hydrogen bonding and hydrophobic interactions hold the two rings of GS together.

Hydrophobe

hydrophobichydrophobicityhydrophobic interaction
Hydrogen bonding and hydrophobic interactions hold the two rings of GS together.

Neurotransmitter

neurotransmittersexcitatory neurotransmitterneurotransmitter system
GS in the brain participates in the metabolic regulation of glutamate, the detoxification of brain ammonia, the assimilation of ammonia, recyclization of neurotransmitters, and termination of neurotransmitter signals.

Astrocyte

astrocytesastrogliaastrocytic
GS, in the brain, is found primarily in astrocytes.

Chloroplast

chloroplastschloroplast stromagreen algal derived chloroplast
Plants have two or more isozymes of GSII, one of the isozymes is translocated into the chloroplast.