Urease, enzyme activity

Lomas, M. W. (2004b). Nitrate reductase and urease enzyme activity in the marine diatom Thalassiosira weissjlogii (BaciUariophyceae) Interactions among nitrogen substrates. Mar. Biol. 144, 37 4. 

Enzyme Alkaline phosphatase (3-Galactosidase Peroxidase Urease Enzyme activity Enzyme activity Enzyme activity Enzyme activity... 

Enzyme activity (urease, amidase, dehydrogenase, pl-glucosidase, phosphatase, arylsulfatase, fluorescein diacetate hydrolysis) Laboratory incubation Indicates potential microbial activity and nutrient cycling reactions determined in nonstandard laboratory with specialized equipment highly spatially and temporally variable dependent upon organic inputs Dick et al. (1996) Parham et aL (2002)... 

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)... 

Using quantitative gel electrophoresis (37) and a simple activity stain (37), Blattler examined urease preparations showing evidences of aging changes (38, 38a). When urease, initially electrophoretically homogeneous, was allowed to age in buffer or 50% diol, enzymically active species appeared that had electrophoretic mobilities between the usual bands. These intermediate bands corresponded to a variety of species that differed by approximately 60,000 molecular weight between 240,000 and 480,000, and between 480,000 and 960,000. 

The demonstration of so many enzymically active forms of urease... 

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. 

Solution in 0.1 M acetate buffer, pH 3.5, resulted in an enzymically active species (8n) of 240,000 daltons (46). Tanis and Naylor (47) have reported that at low concentration of protein the 18 S form predominated above pH 5.3 and the 12 S form below pH 4.8. Between these pH values a rapid equilibrium of the 12 S and 18 S species was observed The dissociation behavior of urease at low pH depends on the buffer used. In 0.1 M potassium phosphate buffer, adjusted to pH 2.0 with HC1, a heterogeneous mixture of dissociated forms was obtained (d) with an Mw of about 150,000. In acetate buffer at pH 3.5 dissociation into a 120,000 molecular weight species (4n) was observed (48). In 34% acetic acid at pH 2.2 there is effected a dissociation to subunits (n) of 30,000 daltons (7). This same value was obtained for urease ultracentrifuged in 8 M urea -f- 0.5 M thiol and in performic acid oxidized urease (48). 

Ureases from several sources have been examined for enzymically active low molecular weight forms (47). It was noted that the 12 S forms from jack bean did not hybridize with that from B. pasteurii. It now seems probable that gastric urease is bacterial in origin (85). The oc-... 

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). 

Second, the correlation of change in enzymic activity with the titration of essential sulfhydryl groups has led to a postulation of eight active sites per 480,000 (56). Unfortunately, the possibility of structural changes during such titrations makes interpretation of such data equivocal. However, the observation that urease retained its activity in 8 M urea, where the molecular weight has been reduced at least to 90,000 (7), supports the conclusion above. 

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). 

Batch studies for evaluating immobilized enzyme activity and properties of the "bioplastic" (urease entrapped in PDMS) material were conducted in 250-mL shake flasks in an environmentally controlled shaker/ incubator. 

The activity of the enzyme is also strongly affected by the presence of inhibitors. Fluoride ions inhibit urease (173) and oxalate ions inhibit lactate oxidase (174), but the major inhibitors are heavy-metal ions, such as Ag+, Hg +, Cu " ", organophosphates, and sulfhydryl reagents (/i-chloromercuribenzoate and phenylmercury(II) acetate), which block the free thiol groups of many enzyme active centers, especially oxidase (69). Inhibiting the enzyme electrodes makes it possible to quantify the inhibitors themselves (69), for example, H2S and HCN detection using a cytochrome oxidase immobilized electrode (176). 

Three Ni-confaintng enzymes (see Nickel Enzymes Cofactors) appear to utilize Ni metallochaperones for enzyme activation. UreE appears to function in NP+ delivery to urease. The Klebsiella aerogenes protein binds 6 Ni per dimer, whereas that from Bacillus pasteurii binds a single Ni per dimer. The metal content differences arise from a His-Asp-His sequence near the middle and a histidine-rich region at the carboxyl terminus of the former protein. Truncated K aerogenes UreE protein, missing the His-rich... 

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