Glutamate dehydrogenase reactions

Figure 29-5. The i-glutamate dehydrogenase reaction. NAD(P) means that either NAD or NADP can serve as co-substrate. The reaction is reversible but favors glutamate formation.

Figure 8.10 A summaiy of the processes involved in transdeamination. (1) transamination (2) glutamate dehydrogenase. The glutamate dehydrogenase reaction results in ammonia production. The oxoacids are further metabolised to CO , glucose or fat.

The fumarate produced in step [4] is converted via malate to oxaloacetate [6, 7], from which aspartate is formed again by transamination [9]. The glutamate required for reaction [9] is derived from the glutamate dehydrogenase reaction [8], which fixes the second NH4 " in an organic bond. Reactions [6] and [7] also occur in the tricarboxylic acid cycle. However, in urea formation they take place in the cytoplasm, where the appropriate isoenzymes are available. 

Combined actions of aminotransferase and glutamate dehydrogenase reactions... 

From amino acids Many tissues, but particularly the liver, turn ammonia from amino acids by the aminotransferase and glutamate dehydrogenase reactions previously described. 

The other part of the urea cycle that has occurred is the conversion of the carbons of aspartate to fumarate. The fumarate is recycled back to oxaloacetate through TCA cycle reactions in the mitochondrion. Transamination with glutamate regenerates aspartate. The glutamate comes from the glutamate dehydrogenase reaction. 

Urea can be readily determined by using urease. The ammonia produced is determined by Nesslers reagent (55), by coupling to the NADH dependent glutamate dehydrogenase reaction (56), or by the use of a cation sensitive electrode (57). The latter method permits urea determination over the range of 0.1-50 fxg/ml in a few seconds (19). 

Note that this stoichiometry differs from that of the glutamate dehydrogenase reaction in that ATP is hydrolyzed. Why do prokaryotes sometimes use this more expensive pathway The answer is that the value of AT of glutamate... 

Most ammonia results from the deamination of a single amino acid glutamate, via the Glutamate dehydrogenase reaction ... 

Experience with model calculations for equilibrium isotope effects and kinetic isotope effects, when using conventional TST, shows that the RGM is valid in the common circumstance in which the effects of coupled vibrational motions cancel between reactant and product states, or between reactant and transition states. The natural coupling expected between the various bends and stretches of the bonds in a methyl group is largely the same in the reactant state and transition state in the acetyl transfer example, so the free-energy effects of multiple isotopic substitutions are strictly additive. In the case of the glutamate dehydrogenase reaction of Fig. 

The RGM breakdotvn seen for the glutamate dehydrogenase reaction (Fig. 11.7) was interpreted by Srinivasan and Fisher [53] as evidence for tunneling. Intrinsic nonadditivity had been ruled out based on earlier vibrational analysis calculations for related systems [56, 85]. 

Wasteful, because the formation of L-glutamine from L-glutamate and ammonia requires ATP. This investment of ATP is reflected in the fact that the glutamate synthetase reaction is irreversible, whereas the glutamate dehydrogenase reaction is reversible. 

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