Urease oxidation

Enzyme sensors are based primarily on the immobilization of an enzyme onto an electrode, either a metallic electrode used in amperometry (e.g., detection of the enzyme-catalyzed oxidation of glucose) or an ISE employed in potentiometry (e.g., detection of the enzyme-catalyzed liberation of hydronium or ammonium ions). The first potentiometric enzyme electrode, which appeared in 1969 due to Guilbault and Montalvo [140], was a probe for urea with immobilized urease on a glass electrode. Hill and co-workers [141] described in 1986 the second-generation biosensor using ferrocene as a mediator. This device was later marketed as the glucose pen . The development of enzyme-based sensors for the detection of glucose in blood represents a major area of biosensor research. 

Zaman M, Blennerhassett JD. Effects of the different rates of urease and nitrification inhibitors on gaseous emissions of ammonia and nitrous oxide, nitrate leaching and pasture production from urine patches in an intensive grazed pasture system. Agriculture Ecosystems and Environment. 2010 136 236-246. 

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. 

Variation of the nature of the gate electrode results in the different types of FET. For example, in the metal oxide semiconductor FET (MOS-FET) palladium/palladium oxide is used as the gate electrode. This catalyti-cally decomposes gases such as hydrogen sulphide or ammonia with the production of hydrogen ions, which pass into the semiconductor layer. An enzyme may be coated on the palladium, e.g. urease, which catalyses the production of ammonia from urea and thus provides a device for the measurement of this substrate. 

Sahoo, B., Sahu, S.K., Pramanik, P., 2011. A novel method for the immobilization of urease on phosphonate grafted iron oxide nanoparticle. J. Mol. Catal. B Enzym. 69, 95-102. 

Hevesy first used a radioisotope as a tracer. Warburg. Importance of iron pigments in oxidation. Keilin rediscovered cytochromes. Sumner crystallized urease. The Eggletons and Fiske and SubbaRow isolated phospho-creatine. 

The nickel in urease is nonmagnetic and appears to be in the oxidation state Ni(II). The broad optical absorption spectrum is influenced by ligands to the metal (Fig. 1). The spectrum obtained in the presence of the competitive inhibitor mercaptoethanol, after correction for Rayleigh scattering by the protein (31), shows absorption peaks at 324,380, and 420 nm, with molar absorption coefficients of 1550,890, and 460 A/-1 cm-1, respectively. These were assigned to sulfur-to-nickel charge transfer transitions. The spectrum is changed by addition of other inhibitors, such as acetohydroxamic acid (Fig. IB). Similar... 

In contrast to urease the nickel in other bacterial enzymes appears to have a redox function and to take up oxidation states Ni(I) and/or Ni(III). Fortunately these states have recently become better understood in inorganic systems (see the preceding review in this volume by... 

A number of copper -containing protein compounds are enzymes with an oxidase function (ascorbic acid oxidase, urease, etc 1 and these play an important role in Ihe biological oxidation-reduction system. There is a definite relationship of copper with iron in connection with utilization of iron in hemoglobin function. 

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). 

Enzymes often are known by common names obtained by adding the suffix -ase to the name of the substrate or to the reaction that they catalyze. Thus, glucose oxidase is an enzyme that catalyzes the oxidation of glucose glucose-6-phosphatase catalyzes the hydrolysis of phosphate from glu-cose-6-phosphate and urease catalyzes the hydrolysis of urea. Common names also are used for some groups of enzymes. For example, an enzyme that transfers a phosphate group from ATP to another molecule is usually called a kinase, instead of the more formal phosphotransferase. ... 

It has not been possible so far to establish that Cr is an essential element required by plants, however, addition of Cr to soils deficient in the element has been shown to increase growth rates and yields of potatoes, maize, rye, wheat or oats (Scharrer and Schropp, 1935 Huffman and Allaway, 1973 Bertrand and De Wolf, 1986). Nickel appears to be an essential element for plants (Farago and Cole, 1988). Zerner and coworkers (Dixon et al., 1975) demonstrated that urease isolated from jack bean (Canavalia ensiformis) was a nickel enzyme. Eskew et al. (1983) have shown that Ni is an essential micronutrient for legumes. Most plants contain nickel in the range 1 - 6 mg kg-1 (Vanselow, 1966 Hutchinson, 1981). The uptake of Ni is enhanced by low pH values, and available nickel increases at pH less than 6.5 as a consequence of the breakdown of Ni complexes in the soil with Fe and Mn oxides. Uptake of nickel by plants and questions of toxicity and tolerance have been reviewed by Farago and Cole (1988). Nickel toxicity toward plants has been reviewed by Vanselow (1966) and Hutchinson (1981). 

Horseradish peroxidase (and urease) played an important role in the development of the modern concept of the nature of an enzyme and the role of metal ions (Sumner and Somers, 1943 Willstatter, 1965). The species now known as compound II (HRP-II) formed as a result of the reaction of HRP with H202, was discovered in 1937 (Keilen and Mann, 1937). Later compound I (HRP-I), formed prior to HRP-II was identified (Theorell, 1941). The spectra of HRP-I and HRP-II in the 400 nm (Soret band) region have been determined (Chance, 1949 a, b) and measurements have also been extended to the visible region (Chance, 1952). Formation of HRP-I is first order in H202 and HRP (Chance, 1943) and the -OOH group is essential for the oxidation of HRP by peroxide. The enzymatic cycle can be summarised by the following equations (George, 1952),... 

Urease is an -SH group (thiol) containing enzyme. The cysteine residues of the protein molecule must be in the reduced -SH form in order for the enzyme to be active. Oxidation of these groups will form -S-S-, disulfide bridges, and the enzyme loses its activity. Reducing agents such as cysteine or glutathione can reactivate the enzyme. 

The copolymei(L-Cys, L-Glu) hydrolyzed benzoylarginine derivatives(ethyl ester and amides, 19) with an optimum pH of 6.1 and optimum temperature of 40 C. This pH value corre onds to one of the two optimum pH in the hydrolysis of PNPA. The urease activity was also noted for this copolymer, and increased witii air oxidation of some SH groups (i2<5). 

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