Urease

UREASE, an enzyme from the amidase group, producing hydrolytic cleavage of urea into ammonia and carbonic acid. U. is widely distributed in plants (in bacteria, fungi, legume seeds); also found in some invertebrates, but is absent in vertebrate animals. The most convenient material for obtaining U. is defatted flour from soybeans, from which U. can be easily extracted with water. The temperature optimum for U. is at 50-55°; at 70-75° the enzyme is destroyed. The optimal reaction of the medium is at pH 7.3-7.5. U. is strongly inactivated by arsenic compounds (Rona) and heavy metals (Jacoby). Quantitative determination of U. is based on measuring the ammonia (or CO₂) released from urea under standard conditions. On the same principle is based a number of methods for determining urea in biological objects (see Urine, urine analysis, Erov, blood extractives) by the amount of ammonia or CO₂ released during complete hydrolysis of urea added U. (from soybeans). The action of bacterial U. (Micrococcus ureae) explains the ammoniacal fermentation of urine, observed when urine stands under non-sterile conditions. Lit.: Rukhelman A., Materials on the question of the nature of urease, report I-Isolation of urease, its activity and kinetics, Zhurn. exper. Biol. and med., vol. XIV, 1930; Summer J., Crystalline Urease, Erg. d. Enzymforschung, B. I, 1932; S u m ne r J. u. Kirk J., U'ber die chemical nature of Urease, Zeitschr. f. physiol. Chemie, B. CCV, 1932.