Urease other sources

The second source of biochemicals is molecules excreted from cells such as extracellular enzymes and other organic matter. A typical example is cellulase, which is excreted by fungi such as Penicillium in order to break down wood and woody material into sugars that can be used by the organisms. Other common extracellular enzymes found in soil are ureases and amylases. Often enzymes are associated with clay particles, and in such associations, their activity may be increased, decreased, unchanged, or completely destroyed [15],... 

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. 

Nickel occurs as a cofactor in four enzymes known to date (Walsh and Orme-Johnson, 1987). Ureases from plant and animal sources use two Ni atoms as Lewis acids, a role more typical of Zn. In the other three enzymes, all bacterial. Ni is redox active. In methyl coenzyme M reductase of methanogenic bacteria, Ni is found in a tetrapyrrole (factor F430) and cycles between Ni(ll) and Ni(l). Many bacteria contain Ni-dependent hydroge-nase(s) and methanogenic and acetogenic bacteria have a specific Ni-containing CO... 

The insect uses canavanine as a source of dietary nitrogen for the developing larvae (Rosenthal et al., 1982). Arginase activity that hydrolyzes arginine to orinithine also hydrolyzes canavanine to canaline (38) and urea. Urea cannot be assimiliated directly, rather it is first converted to ammonia. This insect produces about 30 times more urease that most other related insects. Thus, a potentially toxic plant substance is converted into a useful resource. The canaline produced is converted apparently to homoserine (13) and ammonia and thereby detoxified (Rosenthal, 1982 Rosenthal and Berge, 1989). 

In some cases, it is extremely useful to combine various biological elements in the construction of a hybrid biosensor. Many different combinations of enzymes, cells, and other biocomponents are possible. The arginine biosensor [30] was probably the first hybrid sensor combining beef liver slice as a source of arginase and purified urease for the realization of two coupled reactions in the vicinity of the surface of an ammonia sensor ... 

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