Role of Fatty Acids in Simultaneous Regulation of Flux Through Glutaminase and Glutamine Synthetase in Rat Kidney Cortex

Baverel, Gabriel; Michoudet, Christian; Martin, G.

doi:10.1007/978-3-642-69754-8_12

Cited by 7 publications

(6 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The fact that both gluconeogenesis and oxidation of glutamine result in a net production of ATP [6] raises the question of whether the high glutamine concentration used might have induced glutamate accumulation and ATP-wasting cycles such as the glutamine/glutamate cycle. In this respect, it should be underlined that the rate of glutamine utilization by rat kidney tubules is only approximately doubled when the glutamine concentration is increased from a near-physiological concentration (1 mM) [60] to 5 mM (present study). Carbon balance calculations also reveal that, at both 1 and 5 mM glutamine, a high rate of complete oxidation of the glutamine carbon skeleton removed occurs ( [60]; present study); this suggests that the pathways of glutamine metabolism observed with 5 mM glutamine are also functional with more physiological concentrations of this amino acid.…”

Section: Contribution Of Intra-and Intercellular Metabolism To the Rementioning

confidence: 59%

“…In this respect, it should be underlined that the rate of glutamine utilization by rat kidney tubules is only approximately doubled when the glutamine concentration is increased from a near-physiological concentration (1 mM) [60] to 5 mM (present study). Carbon balance calculations also reveal that, at both 1 and 5 mM glutamine, a high rate of complete oxidation of the glutamine carbon skeleton removed occurs ( [60]; present study); this suggests that the pathways of glutamine metabolism observed with 5 mM glutamine are also functional with more physiological concentrations of this amino acid. In agreement with this view is the observation that, despite low glutamate accumulation, concomitant degradation and synthesis of glutamine occurred when glutamine was used at a concentration of 1 mM [60].…”

Section: Contribution Of Intra-and Intercellular Metabolism To the Rementioning

confidence: 59%

See 1 more Smart Citation

Complexity of glutamine metabolism in kidney tubules from fed and fasted rats

Vercoutère

Durozard

Baverel

et al. 2004

Biochemical Journal

View full text Add to dashboard Cite

Glutamine is an important renal glucose precursor and energy provider. In order to advance our understanding of the underlying metabolic processes, we studied the metabolism of variously labelled [13C]glutamine and [14C]glutamine molecules and the effects of fasting in isolated rat renal proximal tubules. Absolute fluxes through the enzymes involved, including enzymes of four different cycles operating concomitantly, were assessed by combining mainly the 13C NMR data with an appropriate model of glutamine metabolism. In both nutritional states, unidirectional glutamine removal by glutaminase was partially masked by the concomitant operation of glutamine synthetase; fasting accelerated glutamine removal by increasing flux solely through glutaminase, without changing that through glutamine synthetase. Fasting stimulated net glutamate degradation only by decreasing flux through glutamate dehydrogenase in the reductive amination direction, but surprisingly did not significantly alter complete oxidation of the glutamine carbon skeleton. Finally, gluconeogenesis from glutamine involved not only substantial recycling through the tricarboxylic acid cycle, but also an important anaplerotic flux through pyruvate carboxylase that was accelerated dramatically by fasting. Thus renal glutamine metabolism follows an unexpectedly complex route that is precisely regulated during fasting.

show abstract

Section: Contribution Of Intra-and Intercellular Metabolism To the Rementioning

confidence: 59%

Section: Contribution Of Intra-and Intercellular Metabolism To the Rementioning

confidence: 59%

Complexity of glutamine metabolism in kidney tubules from fed and fasted rats

Vercoutère

Durozard

Baverel

et al. 2004

Biochemical Journal

View full text Add to dashboard Cite

show abstract

“…The expression of glutamine synthetase in the kidney is thought to limit the release of ammonium ions into the renal vein and the urine. Renal glutamine synthetase activity is greatest in herbivores [42], animals that normally excrete an alkaline urine. However, glutamine synthetase is also expressed in the kidneys of rodents, but not in cat, dog, pig, or human kidneys.…”

Section: Expression Of Glutamine Synthetasementioning

confidence: 99%

Glutamine metabolism: Role in acid‐base balance*

Taylor

Curthoys

2004

Biochem Molecular Bio Educ

108

View full text Add to dashboard Cite

The intent of this review is to provide a broad overview of the interorgan metabolism of glutamine and to discuss in more detail its role in acid-base balance. Muscle, adipose tissue, and the lungs are the primary sites of glutamine synthesis and release. During normal acid-base balance, the small intestine and the liver are the major sites of glutamine utilization. The periportal hepatocytes catabolize glutamine and convert ammonium and bicarbonate ions to urea. In contrast, the perivenous hepatocytes are capable of synthesizing glutamine. During metabolic acidosis, the kidney becomes the major site of glutamine extraction and catabolism. This process generates ammonium ions that are excreted in the urine to facilitate the excretion of acids and bicarbonate ions that are transported to the blood to partially compensate the acidosis. The increased renal extraction of glutamine is balanced by an increased release from muscle and liver and by a decreased utilization in the intestine. During chronic acidosis, this adaptation is sustained, in part, by increased renal expression of genes that encode various transport proteins and key enzymes of glutamine metabolism. The increased levels of phosphoenolpyruvate carboxykinase result from increased transcription, while the increase in glutaminase and glutamate dehydrogenase activities result from stabilization of their respective mRNAs. Where feasible, this review draws upon data obtained from studies in humans. Studies conducted in model animals are discussed where available data from humans is either lacking or not firmly established. Because there are quantitative differences in tissue utilization and synthesis of glutamine in different mammals, the review will focus more on common principles than on quantification.Keywords: Glutamine, metabolic acidosis, glutaminase, glutamine synthetase, phosphoenolpyruvate carboxykinase.The structure and function of proteins and of macromolecular complexes are critically dependent upon the hydrogen ion concentration of the surrounding medium. As a result, higher eukaryotes maintain the pH of the extracellular fluid and of various intracellular compartments within narrow limits. For example in humans, normal arterial plasma pH is 7.40 Ϯ 0.05. Fluctuations in excess of 0.5 pH units from this value are usually lethal. Thus, the maintenance of normal acid-base balance is essential for survival. The major acid generated as a byproduct of catabolism is CO 2 . A normal individual generates ϳ20 mol of CO 2 per day. However, this acid is volatile and is readily expelled by the lungs. The relative concentrations of HCO 3 Ϫ and CO 2 are the primary determinants of plasma pH. The HCO 3 Ϫ / CO 2 system has a pK of 6.1 and would appear to be a relatively ineffective buffer at pH 7.4. This system is made effective by the ability to maintain a constant CO 2 concentration through changes in the rate of respiration. Various diseases of the lung or disorders of the central nervous system can result in either hypo-or hyperventilation [1]. The former c...

show abstract

“…201-202). Several authors have demonstrated that glutamine may be converted into glucose and C02 by rat proximal tubules or slices in vitro (Kamm & Strope, 1972;Baverel & Lund, 1979;Watford et al 1980;Baverel et al 1984). The net provision of energy during glutamine metabolism results from both complete oxidation of its carbon skeleton and, to a lesser extent, gluconeogenesis (Halperin et al 1982).…”

Section: Adaptative Changes In Fuel Selection By the Rat Kidney Durinmentioning

confidence: 99%