Glutamine, biosynthesis from glutamate

Nevertheless the biosynthesis of glutamine proceeds from glutamic acid The dif ference is that the endergonic process m Equation 1 is coupled with the strongly exer gome hydrolysis of ATP... 

S ATP 4- L-glutamate <2, 4, 5> (<2> the enzyme catalyzes the first step in the pathway from glutamate to proline [2,3] <2> enzyme is involved in biosynthesis of proline [4] <4> enzyme form GKl is involved in biosynthesis of L-Pro, enzyme form GK 2 is involved in biosynthesis of glutamine and the function of enzyme form GK 3 has not been found [6] <4> enzyme GK 1 is the first enzyme of the proline biosynthetic pathway... 

Figure 24-9 Biosynthesis of glutamate, glutamine, proline, and lysine from 2-oxoglutarate.

Why did nature waste an ATP in glutamine biosynthesis The lone pair of electrons on an ammonia could have attacked the y-carbonyl group of a glutamate. Subsequent elimination of an oxide ion and release of a-proton from the nitrogen would produce a glutamine without the consumption of an ATP. 

Herbicides that inhibit enzymes important for amino acid synthesis account for 28% of the herbicide market. Just three enzymes are involved the enzyme that adds phosphoenolpyruvate to shikimate-3-phoshate in the pathway leading to aromatic compounds, the enzyme that makes glutamine from glutamate and ammonia, and the first common enzyme in the biosynthesis of the branched-chain amino acids. 

Glutamine is synthesized in pigeon liver homogenates from glutamic acid and ammonia. The reaction requires ATP and a specific enzyme, glutamine synthetase. ADP is formed and inorganic phosphate is released in the reaction. The mechanism of the reaction is similar to that involved in glutathione biosynthesis. 

The biosynthesis of glutamine from glutamic acid and NH3 by enzyme preparations from liver and brain has been shown to require ATP and magenesium (1, 2). It has been found further that hydroxylamine can be substituted for NHs, resulting in the formation of glutamohydroxamic... 

In the biosynthesis of glutamine from glutamate and ammonia it is the y-carboxyl of glutamic acid which is activated, and the cleavage of ATP to provide the 2500-4000 calories for formation of the amide bond takes place so that ADP and P are formed rather than AMP and PP. Glutamic add can also form amide bonds with hydroxylamine, hydrazine or methylamine. 

Glutamine is biosynthesized from glutamate in two steps using ATP and ammonia. Propose a mechanism for this biosynthesis. 

This enzyme [EC 4.1.3.27] catalyzes the reaction of chorismate with glutamine to generate anthranilate, pyruvate, and glutamate. In certain species, this enzyme is part of a multifunctional protein together with one or more other components of the system for the biosynthesis of tryptophan (Le., indole-3-glycerol-phosphate synthase, anthranilate phosphoribosyltransferase, tryptophan synthase, and phosphoribosylanthranilate isomerase). The anthranilate synthase that is present in these complexes has been reported to be able to utilize either glutamine or ammonia as the nitrogen source. However, it has also been reported that when anthranilate synthase is separated from this complex, only ammonia can serve as a substrate. 

In most terrestrial animals, glutamine in excess of that required for biosynthesis is transported in the blood to the intestine, liver, and kidneys for processing. In these tissues, the amide nitrogen is released as ammonium ion in the mitochondria, where the enzyme glutaminase converts glutamine to glutamate and NHj (Fig. 18-8). The NHj from intestine and kidney is transported in the... 

FIGURE 22-20 Biosynthesis of histidine in bacteria and plants. Atoms derived from PRPP and ATP are shaded red and blue, respectively. Two of the histidine nitrogens are derived from glutamine and glutamate (green). Note that the derivative of ATP remaining after step (AICAR) is an intermediate in purine biosynthesis (see Fig. 22-33, step ), so ATP is rapidly regenerated. 

Each tissue, including the bloodstream, has a free amino acid pool. This amounts to a total of about 100 g. By far the largest fraction, 50-80%, is located in muscle. Kidney accounts for about 4%, liver for 10%, and the bloodstream another 4%. Glutamine and glutamate are major components of such pools. Free amino acid pools are in equilibrium with tissue protein. Tissue proteins are in a constant state of turnover, that is, biosynthesis and degradation from and to free amino acids. Only plasma proteins, which are largely synthesized in the liver, are not in equilibrium with the plasma free amino acid pool. 

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