Microorganisms urease

A wide variety of aerobic and anaerobic microorganisms are able to express the enzyme urease (urea amidohydrolase), which catalyses the hydrolysis of urea to ammonia and carbon dioxide.27 So far,... 

Approximately 30% of the urea produced by the liver diffuses into the colon where it is degraded by some of the microorganisms, i.e. those that possess the enzyme urease, to form ammonia... 

The formation and excretion of urea is the primary mechanism by which excess nitrogen, in the form of ammonia, is removed from the body. Surprisingly, it was found that the actual rate of urea synthesis exceeded considerably the rate of excretion of the urea. The interesting question, therefore, is what is the fate of this lost urea The answer is that urea enters the large intestine, where it is degraded by microorganisms that possess the enzyme urease, which catalyses the reaction ... 

Figure 8.32 Urea salvage in humans. Urea diffuses into the colon where it is converted to ammonia in those microorganisms that possess the enzyme urease. The ammonia is used by most microorganisms in the colon to synthesise their protein. Upon death in the colon, these organisms are degraded and the protein is hydrolysed to amino acids, some of which are absorbed by the host to be used for protein synthesis, etc.

The urea is excreted through the kidneys and broken down to carbon dioxide and ammonia by plants and microorganisms. The enzyme urease causes this conversion. 

Urea is not expected to adsorb to suspended solids and sediment. Volatilization from water surfaces is not expected. Urea is rapidly hydrolyzed to ammonia and carbon dioxide in environmental systems by the extracellular enzyme, urease, which originates from microorganisms and plant roots. 

Aquatic microorganisms supply electrons through transplasmamembrane reductases to external solutes, enzymatically catalyze a variety of redox and other reactions on the cell surface, and are a source of dissolved extracellular enzymes. Both bound and dissolved extracellular enzymes are probably significant in maintaining a state of disequilibrium for some redox processes in natural waters and in accelerating some thermodynamically favorable reactions. In addition, as described for nickel and nitrogen in the urease example, these enzymes may also render the chemistry of the various components of aquatic systems highly interdependent. 

Selective behavior monitors specific toxicity and employs enzyme inhibition tests and reporter genes tests. Examples, are use of cholinesterase for organophosphates and urease for heavy metal ions detection and also transgenic microorganism for specific analyte assessment. 

The hypothesis that nickel in animals may function as an enzyme cofactor has been stimulated by the discovery that urease from several plants and microorganisms is a nickel metalloenzyrne (20-25). Dixon al. (20) found that highly purified urease (E.C.3.5.1.5) from jack beans (Canavalia enslformls) contained stoichiometric amounts of nickel,... 

The next group of multimembrane systems comprises membranes sensitized biologically using immobilized enzymes or microorganisms. Species that are directly sensed by an ISE are produced in the enzymatic reaction of the analyte. Examples of such sensors are those used for determination of urea in milk, based on immobilized urease and measurement of a pH change. An example of the application of bacteria strains is the use of immobilized recombinant Escherichia coli coupled with a pH electrode. Such electrodes have been used for determination of cephalosporins. When this bacterial strain is coupled with a CO2 gas sensor, glutamic acid determination can be carried out. 

Pure urea has a nitrogen content of 466 g/kg, which is equivalent to a crude protein content of 466 X 6.25 = 2913 g/kg. Feed urea contains an inert conditioner to keep it flowing freely, and this reduces its nitrogen content to 464 g/kg, equivalent to 2900 g/kg crude protein. Urea is hydrolysed by the urease activity of the rumen microorganisms with the production of ammonia ... 

So far there is no known specific biochemical function for nickel in animal organisms. In plants and microorganisms, some metal-loenzymes containing nickel have been found. Such an enzyme is urease, found in soybeans, other legumes (this enzyme was first isolated from the seeds of the Jack bean, Canavalia ensiformis), rice and tobacco. Molecule of urease (580 kDa) contains 12 nickel atoms in six subunits. In the active enzyme centre, two nickel atoms are coordinated by four histidyl residues and one residue of e-N-carbamoyl lysine, while the carbamoyl group and one molecule of water form a bridge between the two nickel atoms. Urease catalyses the hydrolysis of urea to ammonia and carbamate (carbamic acid), which is hydrolysed spontaneously to hydrogen carbonate (bicarbonate) and ammonium ions ... 

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