Glutaminase-synthase

Glutamine synthase converts NH3 to nontoxic glutamine. Glutaminase releases NH3 for use in urea synthesis. 

The glutamine synthase reaction is important in several respects. First, it produces glutamine, one of the 20 major amino acids. Second, in animals, glutamine is the major amino acid found in the circulatory system. Its role is to carry ammonia to and from various tissues, but principally from peripheral tissues to the kidney, where the amide nitrogen is hydrolysed by the enzyme glutaminase (reaction below) this process regenerates glutamate and free ammonium ion, which is excreted in the urine. 

Liver contains both glutamine synthase and glutaminase, but the enzymes are localised in different cellular locations. This ensures that the liver is neither a net producer nor a net consumer of glutamine the difference in cellular location of these two enzymes allows the liver to scavenge ammonia that has not been incorporated into urea. The enzymes of the urea cycle are located in the same cells as the glutaminase. The result of this differential distribution... 

As stated above, the only other known route for the biosynthesis of PLP is dependent upon R5P, G3P, and glutamine, and is catalyzed by a single enzyme complex. The PLP synthase holoenzyme complex consists of 12 synthase (Pdxl) subunits and 12 glutaminase (Pdx2) subunits that form into a cogwheel-type structure (Figure yj 36.39,41,42,59 subunits decorate the exterior of this cogwheel and catalyze the hydrolysis of... 

Figure 21 (a) Cartoon representation of the wild-type Bacillus subtilis PLP synthase heterodimer (2NV2). The glutaminase... 

Figure 24 (Left) Cartoon representation of the Bacillus subtilis GPATase monomer (1AOO) showing the domain structure and the location of the [4Fe-4S] cluster (spheres). Coloring S - yellow and Fe - red. (Right) Cartoon representation of the Escherichia coli GPATase monomer (1ECF). The glutaminase and synthase domains in both images are colored orange and...

Table 3 Effect of mutating critical tunnel residues on the steady-state glutaminase and synthase activities of Escherichia coli GFAT ...

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