Glutamine synthetase (GS) catalyses the incorporation of ammonium
to glutamate for glutamine biosynthesis, the first step in
inorganic nitrogen incorporation into amino acids.
In higher plants, GS is responsible for the assimilation of
ammonium coming from the soil, nitrogen fixation or nitrate
reduction (primary sources).
In addition, GS has a function in the reassimilation of ammonium
released during several metabolic processes (secondary sources),
including protein and amino acid catabolism, photorespiration and
the biosynthesis of phenylpropanoids.