Editing Ammonia (section)

=== Biosynthesis ===
In certain organisms, ammonia is produced from atmospheric nitrogen by [[enzyme]]s called [[nitrogenase]]s. The overall process is called [[nitrogen fixation]]. Intense effort has been directed toward understanding the mechanism of biological nitrogen fixation. The scientific interest in this problem is motivated by the unusual structure of the [[active site]] of the enzyme, which consists of an {{chem2|Fe7MoS9}} ensemble.<ref>{{cite journal|last1=Igarashi|first1=Robert Y.|last2=Laryukhin|first2=Mikhail|last3=Dos Santos|first3=Patricia C.|last4=Lee|first4=Hong-In|last5=Dean|first5=Dennis R.|last6=Seefeldt|first6=Lance C.|last7=Hoffman|first7=Brian M.|title=Trapping H- Bound to the Nitrogenase FeMo-Cofactor Active Site during H2 Evolution: Characterization by ENDOR Spectroscopy|journal=Journal of the American Chemical Society|date=May 2005|volume=127|issue=17|pages=6231–6241|doi=10.1021/ja043596p|pmid=15853328|bibcode=2005JAChS.127.6231I }}</ref>

Ammonia is also a metabolic product of [[amino acid]] [[deamination]] catalyzed by enzymes such as [[Glutamate dehydrogenase 1#Function|glutamate dehydrogenase 1]]. Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to [[urea]] (by [[liver]]), which is much less toxic, particularly less [[#Basicity|basic]]. This urea is a major component of the dry weight of [[urine]]. Most reptiles, birds, insects, and snails excrete [[uric acid]] solely as nitrogenous waste.