Biosynthetic pathways glutamate

Alanine, aspartate, and glutamate are synthesized by transfer of an amino group to the a-keto acids pyruvate, oxaloacetate, and a-keto-glutarate, respectively. These transamination reactions (Figure 20.12, and see p. 248) are the most direct of the biosynthetic pathways. Glutamate is unusual in that it can also be synthesized by the reverse of oxidative deamination, catalyzed by glutamate dehydrogenase (see p. 249). 

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... 

This pathway is the hub of intermediary metabolism. Four- and five-carbon end products of many catabolic processes feed into the cycle to serve as fuels. Oxaloac-etate and a-ketoglutarate, for example, are produced from aspartate and glutamate, respectively, when proteins are degraded. Under some metabolic circumstances, intermediates are drawn out of the cycle to be used as precursors in a variety of biosynthetic pathways. 

The biosynthetic pathways to glutamate and glutamine are simple, and all or some of the steps occur in most organisms. The most important pathway for the... 

The amino acid and nucleotide biosynthetic pathways make repeated use of the biological cofactors pyridoxal phosphate, tetrahydrofolate, and A-adenosylmethionine. Pyridoxal phosphate is required for transamination reactions involving glutamate and for other amino acid transformations. One-carbon transfers require S-adenosyhnethionine and tetrahydrofolate. Glutamine amidotransferases catalyze reactions that incorporate nitrogen derived from glutamine. 

All amino acids are derived from intermediates in glycolysis, the citric acid cycle, or the pentose phosphate pathway (Fig. 22-9). Nitrogen enters these pathways by way of glutamate and glutamine. Some pathways are simple, others are not. Ten of the amino acids are just one or several steps removed from the common metabolite from which they are derived. The biosynthetic pathways for others, such as the aromatic amino acids, are more complex. 

Alanine and aspartate are synthesized from pyruvate and oxaloacetate, respectively, by transamination from glutamate. Asparagine is synthesized by amidation of aspartate, with glutamine donating the NH4. These are nonessential amino acids, and their simple biosynthetic pathways occur in all organisms. 

Glutamate Dehydrogenase and Glutamate 1397 1. Biosynthetic Pathways from Serine... 

Does it appear to be a paradox that L-glutamate is both the product and an initial reactant in the glutamine biosynthetic pathway Assuming that glutamate synthase (fig. 21.3) is utilized, how can you explain this paradox ... 

PQQ is derived from a peptide precursor that contains conserved glutamate (13) and tyrosine (76) residues. All carbon and nitrogen atoms of the precursor amino acids are incorporated into the product (44). Gene clusters involved in this pathway have been studied in considerable detail. The X-ray structure of the enzyme that catalyzes the final reaction step has been determined, and reaction mechanisms have been proposed on that basis (45). However, details of the biosynthetic pathway are still incompletely understood. 

In some mammalian cells, enzymes comprising partial spans of biosynthetic pathways are inside and some outside the mitochondrial matrix space. Therefore, in the liver, six mitochondrial membrane transport proteins are required for urea synthesis, three for gluconeogenesis [7,8], and three others participate in ammonia-genesis [9] in the kidney. The synthesis of neurotransmitter substances such as acetylcholine, glutamate and y-amino butyric acid requires the participation of metabolite transporters in mitochondrial membranes of nervous tissue [9,10]. 

Coenzyme F430 is a nickel-containing tetrapyrrole that is required by methyl-coenzyme M reductase (Figure 29). It is one of a class of nickel chlorins found in nature.Methyl-coenzyme M reductase catalyzes the last step in methanogenesis, the reduction of methyl-coenzyme M to methane and coenzyme M (step 8, Figure 1). The biosynthesis of F430 follows the common tetrapyrrole biosynthetic pathway from glutamate to... 

Figure 19. Biosynthetic pathways for amino acids in that glutamate family. Abbreviations as in Figure 18. The reactant formed from bicarbonate and used in the production of citmlline is carbamoyl phosphate.

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