Glutamate production in islets of Langerhans: Properties of phosphate-activated glutaminase

Michalik, Mariusz; Nelson, June; Erecińska, Maria

doi:10.1016/0026-0495(92)90102-g

Cited by 24 publications

(29 citation statements)

References 55 publications

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“…The glutaminase activity measured in optimal conditions (50 mmol/l phosphate) in BRIN-BD11 cells (69.9±7.3 nmol/mg protein/min) was similar to that reported previously [20]. The activity was found to be phosphate dependent, decreasing to 47.4±3.2 nmol/mg protein/min in the presence of 10 mmol/l phosphate in agreement with an earlier report of beta-cell phosphate-dependent glutaminase activity [20].…”

Section: Effect Of L-glutamine On D-glucose Metabolismsupporting

confidence: 91%

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13C NMR analysis reveals a link between L-glutamine metabolism, D-glucose metabolism and ?-glutamyl cycle activity in a clonal pancreatic beta-cell line

et al. 2003

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Aims/hypothesis. Pancreatic islet cells and clonal betacell lines can metabolise L-glutamine at high rates. The pathway of L-glutamine metabolism has traditionally been described as L-glutamine→L-glutamate→2-oxoglutarate→oxidation in TCA cycle following conversion to pyruvate. Controversially, the metabolism of D-glucose to L-glutamate in beta cells is not widely accepted. However, L-glutamate has been proposed to be a stimulation-secretion coupling factor in glucose-induced insulin secretion. We aimed to investigate the metabolism of glutamine and glucose by using 13 C NMR analysis. Methods. BRIN-BD11 cells were incubated in the presence of 16.7 mmol/l [1-13 C]glucose, 2 mmol/l [2-13 C]L-glycine or 2 mmol/l [1,2-13 C]glutamine in the presence or absence of other amino acids or inhibitors. After an incubation period the cellular metabolites were extracted using a PCA extract procedure. After neutralisation, the extracts were prepared for analysis using 13 C-NMR spectroscopy.Results. Using 13 C NMR analysis we have shown that L-glutamine could be metabolised in BRIN-BD11 cells via reactions constituting part of the γ-glutamyl cycle producing glutathione. Moderate or high activities of the enzymes required for these pathways of metabolism including glutaminase, γ-glutamyltransferase and γ-glutamylcysteine synthetase were observed. We additionally report significant D-glucose metabolism to L-glutamate. Addition of the aminotransferase inhibitor, aminooxyacetate, attenuated Lglutamate production from D-glucose. Conclusion/interpretation. We propose that L-glutamine metabolism is important in the beta cell for generation of stimulus-secretion coupling factors, precursors of glutathione synthesis and for supplying carbon for oxidation in the TCA cycle. D-glucose, under appropriate conditions, can be converted to L-glutamate via an aminotransferase catalysed step. [Diabetologia (2003[Diabetologia ( ) 46:1512[Diabetologia ( -1521 Keywords Pancreatic beta cells, NMR, γ-glutamyl cycle, L-glutamine, L-glutamate, glutathione. Diabetologia (2003( ) 46:1512( -1521( DOI 10.1007( /s00125-003-1184 13 C NMR analysis reveals a link between L-glutamine metabolism, D-glucose metabolism and γ-glutamyl cycle activity in a clonal pancreatic beta-cell line

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Section: Effect Of L-glutamine On D-glucose Metabolismsupporting

confidence: 91%

“…1). Glutaminase from pancreatic islets was unaffected by ammonia but inhibited by L-glutamate [20]. It has been suggested that in the presence of leucine both a high glutaminase activity and a high flux through GDH are necessary for enhanced insulin secretion.…”

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confidence: 99%

13C NMR analysis reveals a link between L-glutamine metabolism, D-glucose metabolism and ?-glutamyl cycle activity in a clonal pancreatic beta-cell line

et al. 2003

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“…Consequently, ATP generation is probably not sufficient to depolarise the plasma membrane through closure of ATP-sensitive K + channels, a process which is required for cytosolic Ca 2+ increase. Therefore, islet glutamate levels can be markedly increased by exposure to extracellular glutamine and, because of scarce conversion of glutamate to α-ketoglutarate [24], without stimulation of insulin secretion [24,55]. Activation of GDH by L-leucine or its non-metabolisable analogue BCH increases glutamine oxidation and insulin secretion, essentially by enhancing the oxidative deamination of glutamate [25,27,28,29,32,33,56].…”

Section: Discussionmentioning

confidence: 99%

Insulin secretion profiles are modified by overexpression of glutamate dehydrogenase in pancreatic islets

Carobbio¹,

Ishihara²,

Fernández-Pascual

et al. 2004

Diabetologia

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Aims/hypothesis. Glutamate dehydrogenase (GDH) is a mitochondrial enzyme playing a key role in the control of insulin secretion. However, it is not known whether GDH expression levels in beta cells are ratelimiting for the secretory response to glucose. GDH also controls glutamine and glutamate oxidative metabolism, which is only weak in islets if GDH is not allosterically activated by L-leucine or (+/−)-2-aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH). Methods. We constructed an adenovirus encoding for GDH to overexpress the enzyme in the beta-cell line INS-1E, as well as in isolated rat and mouse pancreatic islets. The secretory responses to glucose and glutamine were studied in static and perifusion experiments. Amino acid concentrations and metabolic parameters were measured in parallel.Results. GDH overexpression in rat islets did not change insulin release at basal or intermediate glucose (2.8 and 8.3 mmol/l respectively), but potentiated the secretory response at high glucose concentrations (16.7 mmol/l) compared to controls (+35%). Control islets exposed to 5 mmol/l glutamine at basal glucose did not increase insulin release, unless BCH was added with a resulting 2.5-fold response. In islets overexpressing GDH glutamine alone stimulated insulin secretion (2.7-fold), which was potentiated 2.2-fold by adding BCH. The secretory responses evoked by glutamine under these conditions correlated with enhanced cellular metabolism. Conclusions/interpretation. GDH could be rate-limiting in glucose-induced insulin secretion, as GDH overexpression enhanced secretory responses. Moreover, GDH overexpression made islets responsive to glutamine, indicating that under physiological conditions this enzyme acts as a gatekeeper to prevent amino acids from being inappropriate efficient secretagogues. [Diabetologia (2004) 47:266-276]

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“…Exposure of islets to extracellular glutamine causes a marked increase in their glutamate levels without any increase in insulin secretion (73,74). Glutamine enhances the ion NH 4 ϩ in cells, which has been shown to inhibit insulin release in both mouse and rat islets secondary to intracellular alkalinization (44,75).…”

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confidence: 99%

“…Glutamine enhances the ion NH 4 ϩ in cells, which has been shown to inhibit insulin release in both mouse and rat islets secondary to intracellular alkalinization (44,75). Under certain condi- tions, e.g., in the presence of leucine or by counteracidification, glutamine is capable of eliciting secretion (44,74,76). Therefore, glutamine exhibits dual effects of enhancing and inhibiting insulin release.…”

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confidence: 99%

β-Cell Mitochondria and Insulin Secretion

Wollheim¹,

Maechler²

2002

Diabetes

107

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The ␤-cell mitochondria are known to generate metabolic coupling factors, or messengers, that mediate plasma membrane depolarization and the increase in cytosolic Ca 2؉ , the triggering event in glucose-stimulated insulin secretion. Accordingly, ATP closes nucleotide-sensitive K ؉ channels necessary for the opening of voltage-gated Ca 2؉ channels. ATP also exerts a permissive action on insulin exocytosis. In contrast, GTP directly stimulates the exocytotic process. cAMP is considered to have a dual function: on the one hand, it renders the ␤-cell more responsive to glucose; on the other, it mediates the effect of glucagon and other hormones that potentiate insulin secretion. Mitochondrial shuttles contribute to the formation of pyridine nucleotides, which may also participate in insulin exocytosis. Among the metabolic factors generated by glucose, citrate-derived malonyl-CoA has been endorsed, but recent results have questioned its role. We have proposed that glutamate, which is also formed by mitochondrial metabolism, stimulates insulin exocytosis in conditions of permissive, clamped cytosolic Ca 2؉ concentrations. The evidence for the implication of these and other putative messengers in metabolism-secretion coupling is discussed in this review. Diabetes 51 (Suppl.

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Glutamate production in islets of Langerhans: Properties of phosphate-activated glutaminase

Cited by 24 publications

References 55 publications

13C NMR analysis reveals a link between L-glutamine metabolism, D-glucose metabolism and ?-glutamyl cycle activity in a clonal pancreatic beta-cell line

13C NMR analysis reveals a link between L-glutamine metabolism, D-glucose metabolism and ?-glutamyl cycle activity in a clonal pancreatic beta-cell line

Insulin secretion profiles are modified by overexpression of glutamate dehydrogenase in pancreatic islets

β-Cell Mitochondria and Insulin Secretion

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