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Protein products urease

Bacterial catabolism of oral food residue is probably responsible for a higher [NHj] in the oral cavity than in the rest of the respiratory tract.Ammonia, the by-product of oral bacterial protein catabolism and subsequent ureolysis, desorbs from the fluid lining the oral cavity to the airstream.. Saliva, gingival crevicular fluids, and dental plaque supply urea to oral bacteria and may themselves be sites of bacterial NH3 production, based on the presence of urease in each of these materials.Consequently, oral cavity fNTi3)4 is controlled by factors that influence bacterial protein catabolism and ureolysis. Such factors may include the pH of the surface lining fluid, bacterial nutrient sources (food residue on teeth or on buccal surfaces), saliva production, saliva pH, and the effects of oral surface temperature on bacterial metabolism and wall blood flow. The role of teeth, as structures that facilitate bacterial colonization and food entrapment, in augmenting [NH3J4 is unknown. [Pg.220]

Urease assay. When Proteus mirabilis grows in a urea-containing medium it hydrolyses the urea to ammonia and consequently raises the pH of the medium. This production of urease is inhibited by aminoglycoside antibiotics (inhibitors of protein synthesis Chapter 8). In practice, it is difficult to obtain reliable results by this method. [Pg.481]

As the one of the main end products of protein metabolism in living organisms, urea is a primary source of organic nitrogen in soil (from animal urine, fertilizers, etc.). Monitoring the level of urea is important for medicine, as well as for environmental protection. Urease is an enzyme that breaks the carbon-nitrogen bond of amides to form carbon dioxide, ammonia and water. This enzyme is widely used for determination of urea in... [Pg.370]

The protein nature of enzymes was established through the seminal work of James Sumner. In 1926, Sumner succeeded in isolating the enzyme urease in crystalline form from jack bean meal. This was the first time in history that an enzyme had been obtained in crystalline, though not completely pure, form. Subsequently, Sumner established that the crystalline enzyme was a protein. Urease is an enzyme that degrades one of the human end products of nitrogen metabolism, urea, to ammonia and carbon dioxide ... [Pg.106]

Fig. 3. Proposed reaction cycle for urease. For urea, R = —NH2. Step 1 urea is activated toward nucleophilic attack by O coordination to a nickel ion the =N+H2 is stabilized by interaction with a protein carboxylate. Step 2 nucleophilic attack by a hydroxide ion, coordinated to the second nickel, to form a tetrahedral intermediate. Step 3 breakdown of the tetrahedral intermediate to form a coordinated carbamate ion. Step 4 hydrolysis releases carbamate ion, the initial product of urease on urea. Reproduced, with permission, from Ref. 34. Fig. 3. Proposed reaction cycle for urease. For urea, R = —NH2. Step 1 urea is activated toward nucleophilic attack by O coordination to a nickel ion the =N+H2 is stabilized by interaction with a protein carboxylate. Step 2 nucleophilic attack by a hydroxide ion, coordinated to the second nickel, to form a tetrahedral intermediate. Step 3 breakdown of the tetrahedral intermediate to form a coordinated carbamate ion. Step 4 hydrolysis releases carbamate ion, the initial product of urease on urea. Reproduced, with permission, from Ref. 34.
Ammonium carbamate is formed in citrate or Tris buffer. It is a 480-kDa protein with a pH optimum of 6.0. The enzyme is very specific for urea or hydroxyurea. It is inhibited by heavy metals, while it is stabilized by 1 X 10 M EDTA. The specific activity of urease is very high (10 000 U/mg), but the potential detection sensitivity is lost because the reaction products are difficult to detect. Urease conjugates because of free thiols are not particularly stable. Urease is important in noninstrumented assays because activity can be visualized via pH-sensitive dyes. [Pg.193]

In subsequent steps the initial carbamate product is further hydrolyzed to bicarbonate. Jack bean urease is a hexamer containing two nickel ions per monomeric subunit. It is unusually difficult to remove the metal atoms from the protein, requiring low pH and resulting in irreversible inactivation of the enzyme. There are indications that one nickel ion is more tightly bound than the other and, therefore, that the two sites are inequivalent. [Pg.354]

Laboratory tests such as urease activity, protein dispersibility index (PDI), nitrogen solubility index (NSI), thiamine, and water absorption have been found valuable in monitoring daily production for protein quality. But biological chick and/or rat assays are the only reliable means currently available for predetermining the nutritional value of whole soybean protein they must be conducted periodically to verify results of chemical tests (31). If whole soybeans are to be used in a mixture containing 20% or more soybean meal, 5% or more urea, and 20% or more molasses, or an equivalent mixture, and exposed to hot, humid storage conditions, it is advisable that the urease activity of the whole soybeans not exceed 0.12 increase in pH (31). Extruded or roasted soybeans properly treated for cattle to increase bypass protein should have urease values of less than 0.05 pH rise. A urease rise of 0.05-0.20 is an indication of proper treatment for swine and poultry. [Pg.2306]

This reaction is one that you may have observed if you have a cat Urea is a waste product of the breakdown of proteins and is removed from the body in urine. Bacteria in kitty litter produce urease. As the urease breaks down the urea in the cat urine, the ammonia released produces the distinctive odor of an untended litter box. [Pg.598]


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Urease

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