UREASE

From Big Medical Encyclopedia

UREASE (carbamide aminohydrolase; KF 3. 5. 1. 5) — the enzyme belonging to the class of hydrolases and catalyzing hydrolytic decomposition of urea with formation of ammonia and carbon dioxide (carbon dioxide gas):


At. provides implementation of an important link in a nitrogen cycle in the nature: animals, eating phytalbumins, emit urea (see), the soil bacteria containing At., decompose urea to the ammonia and carbon dioxide gas which is formed in this reaction ammonia it is used by other soil bacteria for synthesis of nitrites (see) and nitrates (see), to-rye are in turn used by plants for formation of protein etc. High specificity At. concerning urea (even close on structure to urea its methyl derivative is not treated to action of enzyme, only oksiproiz-water urea partially has ability to serve as substrate for At.) allows to use this enzyme for analytical definition of urea in urine and blood that is important diagnostic test at diseases of a liver and kidneys.

At. occurs approximately at 200 species of bacteria, at many pleseny and at a large number of the higher plants. In a human body and animals At. it is formed by a bacterial flora.

At. was the first enzyme received in a crystal look. It was allocated by Sumner (J. Century of Sumner) in 1926 from beans of a jack bean (Canavalia ensiformis). Enzyme crystallizes from 32% of acetone in the form of colourless octahedral crystals. Pier. the weight (weight) of crystal urease 483000, an isoelectric point (see) is at pH 5,0 — 5,1. Urease gives nitroprussiate reaction, contains suljfgidriljny groups (see).

Optimum of action At. note at pH 7,0, however this size changes depending on the nature and concentration of the applied buffer solution, and also from concentration of substrate — urea. At. it is easily inactivated under the influence of ions of heavy metals: silver, mercury, copper, cadmium, lead. Inhibitors U. also salts of fluorine, haloids, borates, quinones, formaldehyde, hydrogen peroxide are. In the presence of a small amount of solution of iodine or caustic silver U. it is besieged and inactivated, however at addition of hydrogen sulfide activity At. in both cases it is recovered. At. it is quickly split and inactivated under the influence of pepsin, papain, and also hydrogen sulfide at pH 4,3, Urease is considered simple protein, globulin. Recently it was established that 2 atoms of nickel are connected with a molecule of enzyme. A role of nickel in functioning At. it is definitely not known, however it is not excluded that he takes part in catalytic process. Kinetics of the reaction catalyzed At., points to existence in a molecule of enzyme of two active centers, but to establish whether they influence at each other or show the action independently, yet it was not possible.

Activity At. measure by amount of the ammonia formed during reaction determined after an otgonka by titration (see. Titrimetric analysis) or with Nessler's reagent (see Nessler a reactant), and also a manometrical method by training of carbon dioxide gas. In this case for full release of carbon dioxide gas use the acetate or phosphatic buffer with pH 6,0.

At. long ago drew to itself attention of researchers. This interest was connected with ammoniac fermentation of urine (see), a cut occurs under the influence of bacterial enzyme. At nek-ry patol. processes, especially at cystitis (see), urine already from a bladder is emitted in a condition of alkaline fermentation. Under action At. neutral urea is translated in carbonic akhm-moniya, having alkali reaction. Thereof urine becomes alkaline, and phosphate salts drop out in a deposit in the form of phosphate magnesium — ammonium (see

Tripeljfosfat) and phosphate Sa3(r04) lime to 2-V draft there is also insoluble acid urate ammonium (see Urine, an urocheras).

Bibliography: Dickson M. and Webb E. Enzymes, the lane with English, t. 1 — 3, M., 1982; M e c of l e r D. Biokhimiya, the lane with English, t. 2, page 40, M., 1980; Webb L. Inhibitors of enzymes and metabolism, the lane with English, M., 1966; Haggis D, etc. Introduction to molecular biology, the lane with English, M., 1967. I. S. Severin.

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