Glutamate dehydrogenase synthesis

Energy-linked transhydrogenase, a protein in the inner mitochondrial membrane, couples the passage of protons down the electrochemical gradient from outside to inside the mitochondrion with the transfer of H from intramitochondrial NADH to NADPH for intramitochondrial enzymes such as glutamate dehydrogenase and hydroxylases involved in steroid synthesis. 

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.

The ammonia can then be utilised for amino acid synthesis in some or all of the microorganisms in the intestine, a process requiring the enzyme glutamate dehydrogenase to incorporate the ammonia into glutamate... 

Examine the bioenergetics of the synthesis of glutamine synthesis from a-ketoglutarate via glutamate synthase or glutamate dehydrogenase (fig. 21.3). Is there a difference ... 

Fig. 1.3 Reactions showing synthesis of glutamate in brain. Aspartate aminotransferase (1) glu-taminase (2) glutamate dehydrogenase (3) GABA aminotransferase (4) alanine aminotransferase (5) ornithine aminotransferase (6) Al-pyrroline 5-carboxylic acid dehydrogenase (7) and asparagine synthetase (8)...

L-6-Hydroxynorleucine, a different key chiral intermediate used for synthesis of the vasopeptidase inhibitor Omapatrilat (Vanlev ), was prepared in 89% yield and > 99% optical purity by reductive amination of 2-keto-6-hydroxyhexanoic acid using glutamate dehydrogenase from beefliver (Hanson, 1999) (Figure 13.22). In an alternative process, racemic 6-hydroxynorleucine produced by hydrolysis of 5-(4-hydroxybutyl)hydantoin was treated with D-amino acid oxidase to prepare a mixture containing 2-keto-6-hydroxyhexanoic acid and L-6-hydroxynorleucine followed by the reductive amination procedure to convert the mixture entirely to L-6-hydroxynorleucine, with yields of 91-97% and optical purities of > 99%. 

Figure 1 Preparation of chiral synthon for vasopeptidase inhibitor enzymatic synthesis of L-6-hydroxynorleucine (1) using glutamate dehydrogenase.

By replacing the NADH-dependent glutamate dehydrogenase, which is the major nitrogen assimilation route in S. cerevisiae, the NADH formation associated with biomass synthesis was reduced, i. e., the stoichiometric coefficient a in Fig. 1 was reduced. 

Utilization of amino acids for gluconeogenesis requires initial removal of their amino groups, usually by transamination linked to subsequent glutamate dehydrogenase activity. The resultant NH4+ is detoxified by urea synthesis. 

Either or both of these compounds in high concentration will favor glutamate synthesis in the reaction catalyzed by glutamate dehydrogenase. This shift of the chemical reaction to the right will result in assimilation of ammonia. 

In the fed state, when there is abundant protein and carbohydrate, dietary protein is hydrolyzed to amino acids. Those amino acids not required for protein synthesis are converted to 2-oxoacids by the aminotransferases. The 2-oxoacids are then converted into lipids and carbohydrate for storage. Glutamate dehydrogenase catalyzes the formation of ammonia from the excess amino groups derived from the amino acids this ammonia is excreted as urea. 

The electroenzymatic reduction of NAD+ was successfully coupled with a synthesis reaction [122]. Hydrogenase from A. eutrophus was applied to regenerate NADH electrochemically during the transformation of a-ketoglutarate into L-glutamate catalyzed by an L-glutamate dehydrogenase (Fig. 27). 

Ornithine and citrulline are amino acids, but they are not used as building blocks of proteins. The formation of NH4 + by glutamate dehydrogenase, its incorporation into carbamoyl phosphate, and the subsequent synthesis of citrulline take place in the mitochondrial matrix. In contrast, the next three reactions of the urea cycle, which lead to the formation of urea, take place in the cytosol. 

Human beings can synthesize 11 of the basic set of 20 amino acids. These amino acids are called nonessential, in contrast with the essential amino acids, which must be supplied in the diet. The pathways for the synthesis of nonessential amino acids are quite simple. Glutamate dehydrogenase catalyzes the reductive amination of a-... 

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