Amino acid metabolism glutamate dehydrogenase

Glutamate dehydrogenase plays a major role in amino acid metabolism. It is a zinc protein, requires NAD+ or NADP+ as coenzyme, and is present in high concentrations in mitochondria of liver, heart, muscle, and kidney. It catalyzes the (reversible) oxidative deamination of L-glutamate to a-ketoglutarate and NH3. The initial step probably involves formation of a-iminoglutarate by dehydrogenation. This step is followed by hydrolysis of the imino acid to a keto acid and NH3 ... 

With respect to amino acid metabolism some of the differences between host and parasite are somewhat subtle. Some parasite enzymes, for example, have properties which are clearly distinct from those of their mammalian counterparts, such as the cofactor dependence and regulation of glutamate dehydrogenases. The utilization of specific amino acids such as proline or the accumulation of others such as alanine reflects a difference in the relative importance of the pathways between parasite and host. Some differences are particularly striking, especially among anaerobic protozoa in... 

Fig. 42.13. Amino acid metabolism in the gut. The pathways of glutamine metabolism in the gut are the same whether it is supplied by the diet (postprandial state) or from the blood (postabsorptive state). Cells of the gut also metabolize aspartate, glutamate, and BCAA. Glucose is converted principally to the carbon skeleton of alanine. a-KG = a-ketoglutarate GDH = glutamate dehydrogenase TA = transaminase.

Amino acid metabolism A artate aminotransferase Alanine aminotransferase Cysteine aminotransferase Tyrosine aminotransferase Leucine aminotransferase Alanine-ketoacid aminotransfoase Ornithine-ketoacid aminotransferase A artate carbamoyl transferase Methionine adenosyl transferase Glutamate decarboxylase Glutamate dehydrogenase Serine hydroxymethyltransferase Aminoacyl-sRNA synthetases... 

L-Glutamate dehydrogenase is the key enzyme in the theory of amino acid metabolism proposed by Braunshtein 8). 

Transamination channels a-amino acid nitrogen into glutamate. L-Glutamate dehydrogenase (GDH) occupies a central position in nitrogen metabolism. 

Figure 8.17 The metabolism of branched-chain amino acids in muscle and the fate of the nitrogen and oxoacids. The a-NH2 group is transferred to form glutamate which is then aminated to form glutamine. The ammonia required for aminab on arises from glutamate via glutamate dehydrogenase, but originally from the transamination of the branded chain amino acids. Hence, they provide both nitrogen atoms for glutamine formation.

Glutamate dehydrogenase A mitochondrial enzyme present in all tissues that metabolizes amino acids. It catalyzes the oxidative deamination of glutamate to a-ketoglutarate using NAD+ as the electron acceptor to also produce nicotinamide adenine dinucleotide (NADH) and ammonia. The enzyme uses the reducing equivalents of nicotinamide adenine dinucleotide phosphate (NADPH) to perform the reverse reaction. 

Figure 4. Schematic representation of the metabolic fate of alanine in hepatocytes. Note that striking differences may exist between mammalian cell types on the one hand and individual amino acids on the other (see text). Solid and broken arrow lines refer to metabolic conversions and transport routes, respectively, and circles in membranes refer to specific transporters. Numbers refer to enzymes involved in alanine metabolism 1, alanine transaminase 2, pyruvate carboxylase 3, malate dehydrogenase 4, glutamate dehydrogenase 5, glutamine synthetase.

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