Glutamate dehydrogenase, function

Figure 8.29 The initial reactions of glutamine metabolism in kidney, intestine and cells of the immune system. The initial reaction in all these tissues is the same, glutamine conversion to glutamate catalysed by glutaminase the next reactions are different depending on the function of the tissue or organ. In the kidney, glutamate dehydrogenase produces ammonia to buffer protons. In the intestine, the transamination produces alanine for release and then uptake and formation of glucose in the liver. In the immune cells, transamination produces aspartate which is essential for synthesis of pyrimidine nucleotides required for DNA synthesis otherwise it is released into the blood to be removed by the enterocytes in the small intestine or by cells in the liver.

What is the function of NADPH in the reactions catalyzed by glutamate dehydrogenase and glutamate synthase ... 

Glutamate dehydrogenase can also use NAD+ for the degradation of glutamate. This reaction is freely reversible the direction of net flux is determined solely by the relative concentrations of the reactants. Thus, this reaction has two equally important functions the assimilation of ammonia or its removal from metabolites. 

Enzymes in this category include alanine and aspartate aminotransferases, glutamate dehydrogenase (GLD), ATP, 5 -nucleotidase (NTP), y-glutamyl transferase (GGT), glutathione S-transferase (GST), and serum cholinesterase (CHE). The aminotransferases and ALP are widely used. They have long been mistakenly called, as a group, liver function tests. They are not, of course, but the habit persists. GGT is widely available in the United States and on automated analyzers. The others have not been adopted as widely. 

Figure 6.8 The scheme used by Pantano and Kuhr to attach glutamate dehydrogenase to the surface of a carbon fiber. Step 1, after electrochemical oxidation of the fiber to produce surface oxygen functionalities, a diamine is attached to the surface using carbodiimide coupling. Step 2, biotin is attached to the other end of the diamine. Step 3, the bound biotin is reacted with avidin to form a biotin-avidin complex attached to the carbon surface. Step 4, biotinylated enzyme is complexed to the avidin to complete construction of the enzyme modified carbon fiber surface. (Adapted from [27].)...

There are at least three types of glutamate dehydrogenases which differ in coenzyme specificity those specific for either NAD or NADP and those that can function with both. For brevity, the first two will be abbre-... 

The same 2-BDB-TeA 2, 5 -DP was also found to inactivate the NADP -specific glutamate dehydrogenase from Salmonella typhimurium. The rate of inactivation exhibited a nonlinear dependence on the reagent concentration, indicative of reversible binding prior to irreversible modification (J9). The presence of NADPH or NADP in the reaction mixture completely prevented inactivation, suggesting that 2-BDB-TcA 2, 5 -DP also functioned as an affinity label of the coenzyme site in this NADP -specific dehydrogenase. 

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