Enzymatic Reaction (image will open in a new window)
Urease catalyzes the hydrolysis of urea:
Jespersen (1975) reports that ammonium carbamate is produced in citrate and Tris buffer.
Urease occurs in many bacteria, several species of yeast and a number of higher plants. Varner (1960) has reviewed it. Two of the best sources are: Jack beans (Canavlia ensiformis) from which it has been crystallized and thoroughly studied, and Bacillus pasteurii.
The enzyme is important in assaying for urea. See Guilbault and Montalvo (1970). Its immobilization has been reported: et al. (1974), James and Pring (1975), Messing (1974), Nakamoto et al. (1975), Sundaram (1973) and Tran-Minh and Broun (1975).
Characteristics of Urease from Jack Bean:
Molecular weight: 480,000 (Fishbein et al. 1970).
Composition: Monomeric (a)urease can polymerize to form six unit polymers of about three million daltons. (Fishbein et al. 1970; Fishbein and Nagarajan 1972a). Andrews and Reithel (1970) report on the sulfhydryl groups. Contaxis and Reithel (1971) indicate the molecule can be split in half with no loss of activity. See also Contaxis and Reithel (1972), Fishbein and Nagarajan (1972b), Lynn (1970), and Bailey and Boulter (1969).
Optimum pH: 7.4 (Cesareo and Langton, 1992).
Km: 1.3mM in Tris⋅HCl (Cesareo and Langton, 1992).
Inhibitors: Heavy metals. NH4+ ions formed. See also Fishbein and Carbone (1965). Sodium and potassium ions are inhibitors (Cesareo and Langton, 1992).
Specificity: Urease is specific for urea and hydroxyurea (Fishbein and Carbone 1965). See also Sundaram and Laidler (1970).
Stabilizers: EDTA in concentrations of 1 X 10-3 M. 50% glycerol solutions protect urease crystalline suspension for several months at 4°C.
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