Glutamate synthase reactions

As described in Section III,B, 1,2-oxogJutarate has to be transported into the chloroplast in order to take part in the glutamate synthase reaction. A founda-... 

The activity of carbamoyl phosphate synthase I is determined by A -acetylglutamate, whose steady-state level is dictated by its rate of synthesis from acetyl-CoA and glutamate and its rate of hydrolysis to acetate and glutamate. These reactions are catalyzed by A -acetylglu-tamate synthase and A -acetylglutamate hydrolase, respectively. Major changes in diet can increase the concentrations of individual urea cycle enzymes 10-fold to 20-fold. Starvation, for example, elevates enzyme levels, presumably to cope with the increased production... 

This redox protein participates in several enzyme-catalyzed reactions, including glutamate synthase (ferredoxin) [EC 1.4.7.1] ferredoxin-nitrite reductase [EC... 

Glutamate synthase (NADPH) [EC 1.4.1.13], an iron-sulfur flavoprotein, catalyzes the reaction of L-glutamine with a-ketoglutarate (or, 2-oxoglutarate) and NADPH to produce NADP+ and two glutamate molecules. Ammonia can act as the nitrogen donor substrate instead of L-glutamine, albeit weaker. 

A major class of enzymes that catalyze oxidation-reduction reactions. This class includes dehydrogenases, reductases, oxygenases, peroxidases, and a few synthases. Examples include alcohol dehydrogenase (EC 1.1.1.1), aldehyde oxidase (EC 1.2.3.1), orotate reductase (EC 1.3.1.14), glutamate synthase (EC 1.4.1.14), NAD(P) transhydrogenase (EC 1.6.1.1), and glutathione peroxidase (EC 1.11.1.9). 

In bacteria and plants, glutamate is produced from glutamine in a reaction catalyzed by glutamate synthase. a-Ketoglutarate, an intermediate of the citric acid cycle, undergoes reductive amination with glutamine as nitrogen donor ... 

The net reaction of glutamine synthetase and glutamate synthase (Eqns 22-1 and 22-2) is... 

While reductive animation of glutamate via glutamate synthase appears to be the major pathway for incorporation of nitrogen into amino groups, some direct animation of pyruvate and other 2-oxoacids in reactions analogous to that of glutamate dehydrogenase occurs in bacteria.105 106 Another bacterial enzyme catalyzes reversible addition of ammonia to fumarate to form aspartate (p. 685). 

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

Glutamate from glutamine Glutamine can be a precursor for the synthesis of glutamate, with the reaction of glutamate synthase, also known as GOGAT (glutamine ... 

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. 

Plasma folylmonoglutamates are transported into cells, where they are converted to the polyglutamyl form, an event catalyzed by folylpoly glutamate synthase. This enzyme uses telrahydrofolates as a substrate. It seems not to recognize or use S-methyl-Hifolates. Hence, the 5-methy 1-Hifolate absorbed from the bloodstream must be converted to folate prior to polyglutarnation. The reaction (KCurs in a... 

Glutamate synthase (GltS) catalyzes the conversion of 2-oxoglutarate into L-glutamate with L-glutamine serving as the nitrogen source for the reaction (Equation (26)). 

Oxogiutarate NHs Scheme 32 Two reactions cataiyzed by glutamate synthase. 

The only multisite Ping-Pong mechanism known in 1970 was that of transcarboxylase (methylmalonyl-CoA carboxyltransferase) (33), but a number have been identified since then, including not only reactions in which biotin, lipoic acid, and 4-phosphopantetheine are carriers between active sites, but also reactions where oxidation and reduction of a group on the enzyme occur at different sites [e.g., glutamate synthase (34)]. 

These values are calculated from the stoichiometry of glutamate to 5 -phosphorlbosylamlhe, ahd therefore represent the fractloh of ammonia released by glutamine hydrolysis that Is used In the synthase reaction. All values for the mutaht ehzymes are normalized to that of WT GPATase (0.90). 

Bacteria growing with ammonia as their sole nitrogen source use this reaction as the primary route for nitrogen assimilation, fri animal cells, the reversible reaction can function in either direction. The enzyme is allosterically regulated. ATP or GTP inhibits its action. Glutamate synthase catalyzes a similar reaction ... 

The reductant can be NADH, NADPH (in yeast and bacteria), or reduced ferredoxin (in plants). The enzyme that catalyzes this reaction is glutamate synthase it is also known as glutamate oxoglutarate aminotransferase (GOGAT). A GS/GOGAT complex exists in plants and allows them to cope with conditions of limited nitrogen availability. Enzymes that catalyze transamination reactions require pyridoxal phosphate as a coenzyme (Figure 23.8). We discussed this compound in Section 7.8 as a typical example of a coenzyme, and here we can see its mode of action in context. 

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