Urea is the excreted form of the ammonia (NH3) which is released during the process of metabolism of amino acids in the liver. At physiological pH values, it is present in the body in the form of ammonium ion (NH4+). Both ammonia and ammonium ion are toxic and in high concentration cause severe brain damage. Therefore, ammonia has to be effectively inactivated and excreted. All mammals and terrestrial vertebrates, including humans, convert ammonia to urea before excretion.

Urea (H2N-CO-NH2) is a diamide of carbonic acid. It is neutral, relatively non-toxic, and produced only in the liver.

The enzyme urease catalyzes the decomposition of urea to ammonia and carbon dioxide. It is present in large quantities in the intestines of ruminants.

Urease, produced by many bacteria species, is thought to play a major role in the production of infection-induced urinary stones. The bacteria surrounds itself with a layer of ammonia, which neutralizes acid in its immediate vicinity and enhances their survival. Alkalinization of the urine by ammonia can cause magnesium phosphate and calcium phosphate to become supersaturated and crystallize out of solution to form, respectively, struvite and apatite stones. Bacteria within the stones may be resistent to antimicrobial therapy. Large stones may interfere with kidney function. The ammonia produced by urease activity may also damage the epithelium of the urinary tract. 1

  1. Baron S, editor. Galveston (TX): University of Texas Medical Branch at Galveston. Medical Microbiology. 4th edition.
  2. Jan Koolman, Klaus-Heinrich Röhm. Color Atlas Of Biochemistry