Urease function

Cheng G, N Shapir, MJ Sadowsky, LP Wackett (2005) Allophanate hydrolase, not urease functions in bacterial cyannric acid metabolism. Appl Environ Microbiol 71 4437-4445. 

By the end of the nineteenth century a more descriptive system was in use. The suffix -ase was appended to the name of the substrate involved in the reaction, eg, amylase, ceUulase, protease, Hpase, urease, etc. Names that reflected the function of the enzyme with the suffix -ase were also used, eg, invertase, transferase, isomerase, oxidase. 

Hemodialysis with microencapsulated urease and an ammonia ion adsorbent, zirconium phosphate [13772-29-7], has been used (247) to delay the onset of dialysis therapy in patients retaining some renal function, and to reduce the time between dialysis treatment. 

Biomimetic chemistry of nickel was extensively reviewed.1847,1848 Elaborate complexes have been developed in order to model structural and spectroscopic properties as well as the catalytic function of the biological sites. Biomimetic systems for urease are described in Section 6.3.4.12.7, and model systems for [Ni,Fe]-hydrogenases are collected in Section 6.3.4.12.5. 

Nickel Essential trace element Chicks and rats raised on deficient diet show impaired liver function and morphology stabilizes coiled ribosomes. Active metal in several hydrogenases and plant ureases Very toxic to most plants, moderately so to mammals carcinogenic. Local industrial pollutant of air and water. 

Nickel has long been suspected to be an essential trace element for living organisms, but the identification of its functions in molecular terms is relatively recent. The first nickel protein to be identified was urease (urea ammonia hydrolase) (i). This was demonstrated 49 years after the original isolation and crystallization of the enzyme by Sumner (2). This enzyme is of widespread occurrence, and the specific requirement for nickel explains many of the effects of nickel deficiency in plants (3, 4). 

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... 

The four types of nickel-containing enzymes are quite distinct in the coordination sites and catalytic function of the nickel centers. In urease, the nickel appears to be bound to oxygen and nitrogen ligands and appears to remain as Ni(II), a state which favors octahedral or square-planar coordination. The function of nickel in this unique case may be analogous to that of zinc in other hydrolases such as carboxypeptidase. 

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. 

Bacteria-free cultures of blue-green algae yielded extracts in which urease could be demonstrated (80,81). Again, in algae as in bacteria (69) the function of urease is conjectural (82). 

Much uncertainty reigned over the nature of proteins, the best known of which were hemoglobin, the digestive enzymes, and later, insulin. Properties of individual amino acids and the peptide bond were studied early in this century, but it was not until urease was crystallized by Sumner1 in 1926, followed by the isolation of other pure enzymes, that it was finally accepted in the 1930s that enzymes were proteins and that their catalytic properties were not the function of some adsorbed low molecular weight entity. Somewhat later, towards the end of the 1930s, coenzymes were isolated and their roles established. 

L. Holm and C. Sanders, An evolutionary treasure unification of a broad set of amidehydrolases related to urease, Protein Structure, Function, and Genetics 1997, 28, 72-82. 

Figure 2 shows the results obtained when this polymer, containing dispersed hydrocortisone, is surrounded by a hydrogel containing immobilized urease and release of hydrocortisone is studied as a function of external urea concentration (2). Although this system has very little therapeutic relevance, it did establish the feasibility of this concept and served as the basis for the development of a more useful system. 

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