Urease is the enzyme that breaks down urea into ammonia and carbon dioxide or ammonium and carbonate ions. Since the reaction takes place in aqueous solution, some hydrogen carbonate ions are also formed to some extent. Urease is a group of amidase and can be found in plant seeds, bacteria, crabs and seashells. Regardless of the urea-splitting function, plant urease acts as an insecticide. It causes platelet aggregation in mammal blood. In particular, the urease contained in soil bacteria plays an important role in the nitrogen cycle: Since the urea contained in liquid manure is resistant to decomposition in the absence of enzymes, nitrogen fertilization without urease would be impossible. On the other hand, urease-positive bacteria in the excrements are responsible for undesirable ammonia emissions in agricultural livestock farming. The reaction speed is significantly increased due to the catalytic activity of the enzyme (of about a factor of 1014). The urease contained in beans (and probably also in bacteria) is a metalloenzyme and contains nickel.