When a plant or animal dies or an animal expels waste, the initial form of nitrogen is organic. Bacteria or fungi convert the organic nitrogen within the remains back into ammonium (), a process called ammonification or mineralization. Enzymes involved are:
* GS: Gln Synthetase (cytosolic & plastic)
* GOGAT: Glu 2-oxoglutarate aminotransferase (Ferredoxin & NADH-dependent)
* GDH: Glu Dehydrogenase:
** Minor role in ammonium assimilation.
** Important in amino acid catabolism.