Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.4.1.2 (glutamate dehydrogenase)
 4,380 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Kinetic analyses done with cell-free extracts of this basidiomycete fungus showed that the NADP-linked glutamate dehydrogenase exhibited positively co-operative interactions with the substrates 2-oxoglutarate and NADPH, negatively co-operative kinetics with NADP+ and was extremely sensitive to inhibition of deamination activity by ammonium and/or ammonia. The NAD-linked enzyme showed positive co-operativity with NADH, Michaelis-Menten kinetics with all other substrates and was subject only to mild inhibitions by the reaction products. Considered together with the values of the Michaelis constants, these results indicate that the former enzyme is primarily concerned with the amination of 2-oxoglutarate when the concentration of this substrate exceeds about 4 mM, while the NAD-linked enzyme is able to aminate or deaminate as metabolic conditions require. Synthesis of both enzymes was repressed by addition of carbamyl phosphate or N-acetyl-glutamate to mycelial cultures growing in media containing glucose and ammonium as carbon and nitrogen sources. Growth in media containing urea results in repression of the NADP-linked glutamate dehydrogenase and derepression of the NAD-linked enzyme. Such results indicate a connexion between the glutamate dehydrogenases and the urea cycle. It is suggested that under normal conditions of growth on complex media nitrogen is assimilated in the form of amino acids and that the glutamate dehydrogenases act in support of transaminases to allow this process to continue, and in support of the urea cycle to allow the disposal of excess nitrogen.
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PMID:Factors affecting the amount and the activity of the glutamate dehydrogenases of Coprinus cinereus. 1 62

Acetylglutamate in HClO4 tissue extracts is first separated from glutamate by ion exchange. It is then deacylated with aminoacylase, and the resulting glutamate, after adsorption to and elution from an AG 50 column, is quantitated by a fast-HPLC method using o-phthaldialdehyde precolumn derivatization, separation in a C18 reverse-phase column, and fluorescence detection. A linear response is obtained up to 2 nmol, the detection limit is 5 pmol, and the method is suitable for assay in 1 mg liver tissue and thus for needle biopsies. When samples were analyzed by this procedure and by earlier procedures based upon detection of glutamate with glutamate dehydrogenase or upon activation of carbamoyl phosphate synthetase the results were similar. The method, which is highly specific, compares favorably in sensitivity, precision, and accuracy with all other published procedures. Using this assay, no acetylglutamate has been found in chicken liver and rat kidney.
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PMID:Determination of N-acetyl-L-glutamate using high-performance liquid chromatography. 399 35

This study examines the role of glucagon and insulin in the incorporation of (15)N derived from (15)N-labeled glutamine into aspartate, citrulline and, thereby, [(15)N]urea isotopomers. Rat livers were perfused, in the nonrecirculating mode, with 0.3 mM NH(4)Cl and either 2-(15)N- or 5-(15)N-labeled glutamine (1 mM). The isotopic enrichment of the two nitrogenous precursor pools (ammonia and aspartate) involved in urea synthesis as well as the production of [(15)N]urea isotopomers were determined using gas chromatography-mass spectrometry. This information was used to examine the hypothesis that 5-N of glutamine is directly channeled to carbamyl phosphate (CP) synthesis. The results indicate that the predominant metabolic fate of [2-(15)N] and [5-(15)N]glutamine is incorporation into urea. Glucagon significantly stimulated the uptake of (15)N-labeled glutamine and its metabolism via phosphate-dependent glutaminase (PDG) to form U(m+1) and U(m+2) (urea containing one or two atoms of (15)N). However, insulin had little effect compared with control. The [5-(15)N]glutamine primarily entered into urea via ammonia incorporation into CP, whereas the [2-(15)N]glutamine was predominantly incorporated via aspartate. This is evident from the relative enrichments of aspartate and of citrulline generated from each substrate. Furthermore, the data indicate that the (15)NH(3) that was generated in the mitochondria by either PDG (from 5-(15)N) or glutamate dehydrogenase (from 2-(15)N) enjoys the same partition between incorporation into CP or exit from the mitochondria. Thus, there is no evidence for preferential access for ammonia that arises by the action of PDG to carbamyl-phosphate synthetase. To the contrary, we provide strong evidence that such ammonia is metabolized without any such metabolic channeling. The glucagon-induced increase in [(15)N]urea synthesis was associated with a significant elevation in hepatic N-acetylglutamate concentration. Therefore, the hormonal regulation of [(15)N]urea isotopomer production depends upon the coordinate action of the mitochondrial PDG pathway and the synthesis of N-acetylglutamate (an obligatory activator of CP). The current study may provide the theoretical and methodological foundations for in vivo investigations of the relationship between the hepatic urea cycle enzyme activities, the flux of (15)N-labeled glutamine into the urea cycle, and the production of urea isotopomers.
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PMID:Studies of hepatic glutamine metabolism in the perfused rat liver with (15)N-labeled glutamine. 1050 42

This review focuses on the role of acute pH changes in the regulation of Gln/Glu metabolism in the kidney, liver, and brain. Alterations of proton concentration ([H(+)]) profoundly affect flux through phosphate-dependent glutaminase (PDG) or glutamate dehydrogenase (GDH), the primary enzymes responsible for mitochondrial metabolism of glutamine and glutamate, respectively. In the kidney, acute acidosis stimulates Gln uptake and its metabolism via the PDG pathway. The Glu formed from Gln can be removed via 1) oxidative deamination through the GDH reaction, 2) transamination reactions, and 3) transport of Glu from intracellular to extracellular compartment, thereby diminishing the intramitochondrial pool of glutamate sufficiently to stimulate flux through the PDG pathway. Converse changes may occur with increased pH. In the liver, acidosis diminishes the rate of Gln and Glu metabolism via the PDG and GDH pathways, but stimulates glutamine synthesis (i.e., glutamine recycling). Alkalosis has little effect. Hepatic Gln metabolism via the PDG pathway has a central role in ureagenesis via 1) supplementation of nitrogen for the synthesis of carbamyl phosphate, and 2) providing glutamate for N-acetylglutamate synthesis. In the brain, Gln/Glu metabolism links ammonia detoxification and energy metabolism via 1) detoxification of ammonia and excess glutamate by glutamine synthesis in astrocytes, 2) formation and export of glutamine to neurons where it is metabolized to glutamate and GABA, and 3) production of alpha-ketoglutarate and lactate from Glu and their transport to neurons. Changes in intracellular pH associated with changes in cellular [K(+)] may have a key role in the regulation of these processes of glial-neuronal metabolism of Gln/Glu metabolism.
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PMID:Newer aspects of glutamine/glutamate metabolism: the role of acute pH changes. 1051 71

The liver is the major site of gluconeogenesis, the major organ of amino acid catabolism and the only organ with a complete urea cycle. These metabolic capabilities are related, and these relationships are best exemplified by an examination of the disposal of the daily protein load. Adults, ingesting a typical Western diet, will consume approximately 100 g protein/d; the great bulk of this is metabolized by the liver. Although textbooks suggest that these amino acids are oxidized in the liver, total oxidation cannot occur within the confines of hepatic oxygen uptake and ATP homeostasis. Rather, most amino acids are oxidized only partially in the liver, with the bulk of their carbon skeleton being converted to glucose. The nitrogen is converted to urea and, to a lesser extent, to glutamine. The integration of the urea cycle with gluconeogenesis ensures that the bulk of the reducing power (NADH) required in the cytosol for gluconeogenesis can be provided by ancillary reactions of the urea cycle. Glutamate is at the center of these metabolic events for three reasons. First, through the well-described transdeamination system involving aminotransferases and glutamate dehydrogenase, glutamate plays a key catalytic role in the removal of alpha-amino nitrogen from amino acids. Second, the "glutamate family" of amino acids (arginine, ornithine, proline, histidine and glutamine) require the conversion of these amino acids to glutamate for their metabolic disposal. Third, glutamate serves as substrate for the synthesis of N-acetylglutamate, an essential allosteric activator of carbamyl phosphate synthetase I, a key regulatory enzyme in the urea cycle.
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PMID:Glutamate, at the interface between amino acid and carbohydrate metabolism. 1073 67

Somatotropin (ST) treatment promotes animal growth and allows for the conservation of amino acids by increasing nitrogen retention and reducing ureagenesis and amino acid oxidation. To determine whether the improvement in amino acid conservation with ST treatment involves regulation of urea cycle enzyme activities in both liver and intestine, growing swine were treated with either ST (150 microg x kg(-1) x d(-1)) or saline for 7 d. Fully fed pigs (n = 20) were infused intravenously for 2 h with NaH(13)CO(3) followed by a 4-h intraduodenal infusion of [1-(13)C]phenylalanine. Arterial and portal venous blood and breath samples were obtained at baseline and steady-state conditions for measurement of amino acid and blood urea nitrogen (BUN) concentrations and whole-body phenylalanine oxidation. Urea cycle enzyme activities were determined in liver and jejunum. ST decreased BUN (-46%), arterial (-34%) and portal venous (-43%) amino acid concentrations and whole-body phenylalanine oxidation (-30%). The activities of carbamoylphosphate synthase-I (-45%), argininosuccinate synthase (-38%), argininosuccinate lyase (-23%), arginase (-27%), and glutaminase (-18%), but not of ornithine carbamoyltransferase, ornithine aminotransferase, or glutamate dehydrogenase were reduced in liver of ST-treated pigs. ST slightly increased intestinal activity of glutaminase (+9%) but did not affect that of any other enzymes. ST decreased hepatic, but increased jejunal, N-acetylglutamate (an essential allosteric activator of carbamoylphosphate synthase-I; -26% and +32%, respectively) and carbamoylphosphate (a substrate for ornithine carbamoyltransferase; -20% and +28%, respectively) content. These results demonstrate that the reduced amino acid catabolism with ST treatment in growing pigs involves a reduction in hepatic urea cycle enzyme activities. The effect of ST treatment on porcine urea cycle enzymes is tissue-specific and is associated with a reduction in substrate availability for hepatic ureagenesis.
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PMID:Somatotropin-induced amino acid conservation in pigs involves differential regulation of liver and gut urea cycle enzyme activity. 1177 9

The present study was designed to determine: (i) the role of the reductive amination of alpha-ketoglutarate via the glutamate dehydrogenase reaction in furnishing mitochondrial glutamate and its transamination into aspartate; (ii) the relative incorporation of perfusate 15NH4Cl, [2-15N]glutamine or [5-15N]glutamine into carbamoyl phosphate and aspartate-N and, thereby, [15N]urea isotopomers; and (iii) the extent to which perfusate [15N]aspartate is taken up by the liver and incorporated into [15N]urea. We used a liver-perfusion system containing a physiological mixture of amino acids and ammonia similar to concentrations in vivo, with 15N label only in glutamine, ammonia or aspartate. The results demonstrate that in perfusions with a physiological mixture of amino acids, approx. 45 and 30% of total urea-N output was derived from perfusate ammonia and glutamine-N respectively. Approximately two-thirds of the ammonia utilized for carbamoyl phosphate synthesis was derived from perfusate ammonia and one-third from glutamine. Perfusate [2-15N]glutamine, [5-15N]glutamine or [15N]aspartate provided 24, 10 and 10% respectively of the hepatic aspartate-N pool, whereas perfusate 15NH4Cl provided approx. 37% of aspartate-N utilized for urea synthesis, secondary to the net formation of [15N]glutamate via the glutamate dehydrogenase reaction. The results suggest that the mitochondrial glutamate formed via the reductive amination of alpha-ketoglutarate may have a key role in ammonia detoxification by the following processes: (i) furnishing aspartate-N for ureagenesis; (ii) serving as a scavenger for excess ammonia; and (iii) improving the availability of the mitochondrial [glutamate] for synthesis of N -acetylglutamate. In addition, the current findings suggest that the formation of aspartate via the mitochondrial aspartate aminotransferase reaction may play an important role in the synthesis of cytosolic argininosuccinate.
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PMID:Role of the glutamate dehydrogenase reaction in furnishing aspartate nitrogen for urea synthesis: studies in perfused rat liver with 15N. 1293 93