
Helicobacter Pylori Urease drawn from .
'Urease' () is an
enzyme that
catalyzes the
hydrolysis of
urea into
carbon dioxide and
ammonia. The reaction occurs as follows:
(NH2)2CO + H
2O →
CO2 + 2
NH3
In
1926 James Sumner showed that urease is a
protein. Urease is found in
bacteria,
yeast and several higher
plants.
Characteristics:
★
Active site metal: nickel(II)
★
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
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 (
). 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
Organisms that produce urease tend to be gastrointestinal or urinary tract pathogens, since urease enables them to neutralize the acid present in these acidic environments.
Urease-positive pathogens include:
★
Helicobacter pylori
★
Enteric bacteria including
Proteus,
Klebsiella and
Serratia
★
Nocardia, a filamentous bacterium
★
Ureaplasma urealyticum, a relative of the
mycoplasma
★
Cryptococcus, an
opportunistic fungus