Urease

• UniProt: P18314

• CAS Number: 9002-13-5

Urease is the enzyme that urea into ammonia and carbon dioxide, or into ammonium ions and carbonate ions ( sometimes in bicarbonate ions ), since the reaction takes place in aqueous solution, split:

Or

Urease belongs to the group of amidases and often occurs in plant seeds, bacteria, crabs and sea shells. Pflanzenurease acts independently of the urea -splitting function as an insecticide and produced in mammalian blood platelet aggregation.

In particular, the urease in soil bacteria plays an important role in the nitrogen cycle, because without them would be a nitrogen fertilization by the decomposition-resistant in the absence of enzymes of urea, a component of the manure, not possible. On the other hand, are urease - positive bacteria in the feces the cause of unwanted emissions of ammonia in livestock farming ( in Germany in 2005, an estimated 490,000 of 590,000 tonnes of total ammonia emission).

By the catalytic activity of the enzyme, the rate of reaction is greatly increased by a factor of 1014. The urease from beans ( and probably also the bacteria ) is a metalloenzyme and contains nickel.

The urease from jack beans was the first enzyme, which could be purified and crystallized in 1926 by James Batcheller Sumner. There were the 1946 Nobel Prize in Chemistry.

Urease is considered due to the structure of the nickel-containing center in organometallic chemistry as a possible model system for the catalytic activation of carbon dioxide. A complex of N- carbamates ( binding of the electron-deficient carbon atom of the carbon dioxide to the electron-rich nitrogen atom of imines / amines) nickel (0 - or 2- valent ) exist as a central atom and are characterized structurally, Infrared spectroscopic investigations have an energy reduction ( activation ) of the thermodynamically very stable C = O double bonds can be detected. However, evidence of the transfer of such " activated " carbon dioxide to other substrates is still pending.

Medical importance

Organisms (eg Helicobacter pylori), which possess urease, are often pathogens of the digestive system because they can survive through the ammonia released in the acidic environment of the stomach. The same applies to the pathological species of the genus Proteus, the so- colonize the urogenital tract. This alkaline reaction of the ammonia is used for the detection of these organisms (see: Helicobacter urease test).

Importance to agriculture

Urease in soil bacteria is a prerequisite for the effect of feces as a nitrogen fertilizer, as only the hydrolytic cleavage of urea makes the nitrogen available as ammonium ions. The intermediate product is, however, ammonia gas, and only small quantities of gas can be absorbed by the moisture of the soil. It therefore always escapes proportion of ammonia and is lost as fertilizer. This proportion is greater, the more concentrated the substance from which urea is present and therefore is most ammonia from stable floor and manure lost. Since ammonia also several ways harmful to the environment and it has been agreed internationally to a narrowing of the emissions, an attempt is made, among other things, with urease inhibitors to solve the problem and to reduce the emission from stables.

Kinetics

The reaction of urease with urea is suitable for illustrating the dependence of the reaction rate of the time when it selects a urea solution with a high concentration. Since the decomposition of urea in aqueous solution ions are produced, can the increase in the ion track on conductivity measurement. Over a longer period, the conductivity increases linearly. The reaction can also be followed by photometric measurement. This is added as an indicator bromothymol blue, the more intense blue colors in the course of the reaction. The absorbance is a measure of the concentration, thereby increasing over a prolonged period also linearly. In the decomposition of urea, the reaction rate over a prolonged period of time is constant. It is for this purpose before the reaction is zero order. The decisive factor is that the substrate concentration, which is here of urea, not too small. For small substrate concentrations can be combined with these experiments, the dependence of the reaction rate on the concentration, the time constant, which illustrate in accordance with the Michaelis- Menten kinetics.

History

The effects of urease were discovered in 1798 by Fourcroy and Vauquelin, in 1861, brought by Louis Pasteur in connection with microorganisms, which were first described in 1864 by Van Tieghem as Micrococcus ureae. 1876 ​​bacterial urease was isolated by muscle and defines the catalytic reaction. Only the discovery of soybean urease by Takeuchi in 1909 and following their production in large quantities made ​​in-depth investigations possible.