Glutamate synthases, reaction catalyzed

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)). 

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 ... 

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 ... 

The urea cycle is a unique function of the liver. Excess ammonia formed in other tissues must be carried in a nontoxic form to the liver. In many tissues glutamine serves as the carrier of excess nitrogen. The glutamine is formed in the tissues in a reaction, catalyzed by glutamine synthase, that combines NH3 with glutamate. 

In plants, algae and many bacteria there is an alternative route for ALA synthesis that involves the conversion of the intact five-carbon skeleton of glutamate in a series of three steps to yield ALA. In all organisms, two molecules of ALA then condense to form porphobilinogen in a reaction catalyzed by ALA dehydratase (also called porphobilinogen synthase) (Fig. 2a). Inhibition of this enzyme by lead is one of the major manifestations of acute lead poisoning. 

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... 

GSH is synthesized in a pathway composed of two reactions. In the first reaction, y-glutamylcysteine synthase catalyzes the condensation of glutamate with cysteine (Figure 14.18). y-Glutamylcysteine, the product of this reaction, then combines with glycine to form GSH in a reaction catalyzed by glutathione synthase. 

The urea cycle enzymes are controlled in the short term by the concentrations of their substrates. Carbamoyl phosphate synthetase I is also allosterically activated by N-acetylglutamate. This latter molecule is a sensitive indicator of the cell s glutamate concentration. (Recall that a significant amount of NH4 is derived from glutamate.) N-acetylglutamate is produced from glutamate and acetyl-CoA in a reaction catalyzed by N-acetylglutamate synthase. 

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. 

NOa". The pattern observed was not the same as the pattern predicted if the assimilation of NH4 occurred via the reactions catalyzed by glutamine synthetase and glutamate synthase. The results suggest that NH4 is being assimilated, at least in part, by glutamate dehydrogenase. 

Reaction 1 is mediated by glutamine synthetase while Reactions 2 and 3 are catalyzed by glutamate synthase and glutamate dehydrogenase respectively. 

Glutamate synthase catalyzes the reductive amination of a-ketoglutarate according to reaction ( )—. The enzyme has been... 

A., Glutamine-Binding Subunit of Glutamate Synthase and Partial Reactions Catalyzed by this Glutamine Amidotransferase, Proc. Natl. Acad. Sci. U.S., 71 4607 (1974). 

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