Urease activity

From the results of the urease activity test summarized in Figure 15, it is clear that the deposition procedure preserved to a certain extent the enzyme catalytic activity. Heating the sample before testing decreased the enzyme in the film by about 30% but did not eliminate it completely. The results of the activity test of two samples are summarized in Table 1 together with reference values for a spontaneous reaction without enzyme. It is necessary to underline that enzymatic activity on spherical supports was higher than the respective value in flat films, which could indicate that apparent catalytic efficiency was improved due to an increased area-to-volume ratio. 

The results of most model studies for Ni-mediated urea degradation reported to date are consistent with a cyanate intermediate. While this differs from the most likely mechanism of urease activity as deduced from protein crystallography, there is still no definitive evidence ruling out a transient Ni-bound cyanate intermediate for the enzyme. 

Moreno J.L, Garcia C., Landi L., Falchini L., Pietramellara G., Nannipieri P. The ecological dose value for assessing Cd toxicity on ATP content and DHA and urease activities of soil. Soil Biol Biochem 2001 33 483 189. 

Fig. 1. Dynamics of urease, acid phosphatase and dehydrogenase activity in soil under Cd pollution (Soil urease activity is expressed as mg NH3-N g 1 dry soil 24 h-1, Soil phosphatase activity is expressed as the mg phenol produced g-1 dry soil 24 h 1, Soil dehydrogenase activity is expressed as mgTPF g-1 dry soil 24 h 1, from Akmal et al. 2005b).

PVA/acrylamide blend membranes prepared on cheese cloth support by y-irradiation induced free radical polymerization can be used for urease entrapment. The enzyme urease is entrapped in the membrane during polymerization process and using glutaraldehyde as cross-linking agent. The main advantage of this blend to this process is that it can be reused a number of times without significant loss of urease activity [292],... 

Table 6.3. Effect of nickel supplementation on hydrogenase and urease activities.

Figure 6.5. Immunoblot of the urease large subunit. Extracts of H. pylori wild type (WT) and a hypA mutant from cells grown without nickel supplementation were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and identified by blotting with an anti-urease large-subunit antiserum. Urease activity was 58pmolmin mg for the wild type and Opmolmin" mg for the hypA mutant.

McGee DJ, May CA, Garner RM, et al. 1999. Isolation of Helicobacter pylori genes that modulate urease activity. J Bacteriol 181 2477-84. 

Because urease activities are much greater in the soil than in the floodwater, the NH4+ is largely formed in the soil as the urea moves downward by mass flow and diffusion. The NH4+, H+ and other reactants will also move between the floodwater and soil-both upward and downward-with NH3 being lost from the floodwater by volatilization. The recovery of N in the crop therefore depends on the rate of movement of urea and its reaction products through the soil and on the rate at which the roots remove N from the downward moving pool. 

The structure of the urease active center is similar to that of adenosine deaminase, an enzyme containing one zinc(II) per active site (though see 48). This enzyme catalyzes the deamination of adenosine to inosine and NH3 (see Scheme 9), a reaction mechanistically related... 

Mustakas et al. (46) evaluated the effects of extruder-processing on nutritional quality, flavor, and stability of the product in an attempt to describe extruder conditions which would be acceptable in all three respects. Urease activity was used as an estimation of trypsin inhibitor activity thus the area between the two urease curves in Figure 2 indicates processing conditions which strike a balance between too much and too little heat treatment, showing optimal nutritional quality. Using the flavor and peroxide value isograms, processing conditions may be chosen such that acceptable flavor and stability may also be achieved. 

The title retains the trivial name for enzymes with the systematic name of urea amidohydrolase and the Enzyme Commission code number of EC 3.5.1.5. Ureases are hydrolases acting on C-N bonds (nonpeptide) in linear amides and thus belong to a group that includes glutaminase, form-amidase, and formyltetrahydrofolate deformylase. The title is plural to emphasize that urease activity may be exhibited by several protein species. Urease, singular, has come to mean by common usage, that particular enzymic protein first crystallized by Sumner from jack bean... 

It is convenient to have a method for the detection and rough estimation of urease activity in gels. A simple staining procedure using cresol red has been described (27), but a more elaborate procedure (28) employing p-nitro blue tetrazolium results in sharper definition. 

Several investigators have presented evidence for low molecular weight forms exhibiting urease activity. Hand (33), in 1939, obtained diffusion data indicating particles of 17,000 daltons or less that retained enzymic activity. More recently, sucrose density gradient ultracentrifugation (34)... 

Urease activity persists unaltered when the enzyme is dissolved in SM urea although the ultracentrifuge data indicate a molecular weight of about 90,000 (7). This form of urease has not been sufficiently characterized but does indicate that neither enzymic activity nor specific activity is dependent upon very high molecular weight aggregates. 

In Azotobacter vinelandii, urease appears to be synthesized only when urea or thiourea is present (75). A study of the urease constitutive in Corynebacterium renale (76) did not reveal features remarkably different from the plant enzyme. A similar conclusion was reached in the characterization of a highly purified enzyme from B. pasteurii (77). Stewart (78) has devised a medium for the detection of urease activity in pseudomonads and has resolved uncertainties that have developed in the literature. It has been reported that Sarcina ureae produces urease as an exoenzyme (79). 

Urease activity in soils has been found to reflect the bacterial count and content of organic matter. The urease isolated from an Australian forest soil (87) was crystallized and found to have a specific activity of 75 Sumner units (S.U.) per mg. The molecular weight species were estimated (sedimentation velocity) to be 42, 131, and 217 X 103. That urease activity persists in soils is shown by the finding that enzymic activities, including urease, could be demonstrated in soil samples over 8000 years old (88). 

There is an extensive older literature describing effects of various ions on urease activity. A recent study employing potentiometry (106) indicated inhibition by copper and zinc, questionable inhibition by nitrate, and slight activation by phosphate. 

However, Thomas and Dimnill (1979) studied the effect of shear on catalase and urease activities by using a coaxial cylindrical viscometer that was sealed to prevent any air-liquid contact. They found that there was no significant loss of enzyme activity due to shear force alone at shear rates up to 106 sec-1. They reasoned that the deactivation observed by Charm and Wong (1970) was the result of a combination of shear, air-liquid interface, and some other effects which are not fully understood. Charm and Wong did not seal their shear apparatus. This was further confirmed, as cellulase deactivation due to the interfacial effect combined with the shear effect was found to be far more severe and extensive than that due to the shear effect alone (Jones and Lee, 1988). 

Imamura, A., Yumoto, T., and Yanai, J. (2006). Urease activity in soil as a factor affecting the succession of ammonia fungi. J. Forest Res. 11, 131-135. 

Calculate the urease activity only for the reaction without the inhibitor. Use the titration data from the first 10 min. of reaction (initial slope). 

What would be the urease activity if you used the slope between 40 and 50 min. instead of the initial slope from your diagram ... 

Your lab ran out of 0.05 N HC1. You found a bottle labeled 0.05 N H2S04. Could you use it for your titration If you do, would your calculation of urease activity be different ... 

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