urease

Helicobacter Pylori Urease drawn from PDB 1E9Z.

Urease (EC 3.5.1.5) is an enzyme that catalyzes the hydrolysis of urea into carbon dioxide and ammonia. The reaction occurs as follows:

(NH₂)₂CO + H₂O → CO₂ + 2NH₃

In 1926 James Sumner showed that urease is a protein. Urease is found in bacteria, yeast and several higher plants.

Characteristics

• Active site
• Molecular weight: 480 kDa or 545 kDa for Jack Bean Urease (calculated mass from the amino acid sequence).
• Optimum pH: 7.4
• Optimum Temperature: 60 degrees Celsius
• Enzymatic specificity: urea and hydroxyurea
• Inhibitors: heavy metals (Pb^- & Pb²⁺)

The multi-subunit enzyme usually has a 3:3 (alpha:beta) stoichiometry with a 2-fold symmetric structure (note that the image above gives the structure of the asymmetric unit, one third of the true biological assembly). An exceptional urease is found in Helicobacter pylori, which combines four of the regular six subunit enzymes in an overall tetrahedral assembly of 24 subunits (α₁₂β₁₂). This supra-molecular assembly is thought to confer additional stability for the enzyme in this organism, which functions to produce ammonia in order to neutralise gastric acid. The presence of urease is used in the diagnosis of Helicobacter species.

As diagnostic test

Many gastrointestinal or urinary tract pathogens produce urease, enabling the detection of urease to be used as a diagnostic to detect presence of pathogens.

Urease-positive pathogens include:

• Helicobacter pylori
• Enteric bacteria including Proteus, Klebsiella and possibly Serratia
• Ureaplasma urealyticum, a relative of the mycoplasma
• Cryptococcus, an opportunistic fungus
• Proteus mirabilis

Other uses

Urease conductometric biosensors for detection of heavy metal ions

This section requires expansion.

Urease conductometric biosensors for detection of heavy metal ions consisting of interdigitated gold electrodes and enzyme membranes formed on their sensitive parts have been used for a quantitative estimation of general water pollution with heavy-metal ions. The measurements of the urease residual activity have been carried out in Tris-HNO3 buffer after preincubation in model metal-salt solution. The detection limits, depending on preincubation time and dynamic ranges, have been determined in model solutions of heavy-metal ions. The sequence of metals ions relative to their toxicity toward urease is: Hg2+ > Cu2+ > Cd2+ > Co2+ > Pb2+ > Sr2+ > . The conditions for practical applications of the biosensors have been investigated and critically evaluated for optimization. Urease reactivation by EDTA after inhibition by heavy-metal ions has been demonstrated. The performance characteristics of the conductometric biosensor are discussed by G. A. Zhylyaka, S. V. Dzyadevichb, Y. I. Korpana, A. P. Soldatkina and A. V. El'skayaa in their paper.