Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.14 (ATP synthase)
 7,042 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have recently shown that leucine culture upregulates ATP synthase beta-subunit (ATPSbeta) and increases ATP level, cytosolic Ca(2+), and glucose-induced insulin secretion in rat islets. The aim is to test whether glucokinase expression is also affected in rat islets and its role in glucose sensitization during leucine culture. Leucine culture increased glucose-induced NAD(P)H level at 1 and 2 days but not at 1 week. The half-maximal effective concentration of the glucose response curve for NAD(P)H was left-shifted from 5-7 to 2-3 mmol/l. The effect was dose dependent and rapamycin insensitive. Leucine culture did not affect glyceraldehyde effects on NAD(P)H. Leucine pretreatment for 30 min had no effects on NAD(P)H levels. Leucine culture for 2 days also increased glucose-induced cytosolic Ca(2+) elevation, ATP level, and insulin secretion. Leucine increase of glucokinase mRNA levels occurred as early as day 1 and lasted through 1 week. That of ATPSbeta did not occur until day 2 and lasted through 1 week. Leucine effects on both mRNAs were dose dependent. The upregulation of both genes was confirmed by Western blotting. Leucine culture also increased glucose-induced insulin secretion, ATP level, glucokinase, and ATPSbeta levels of type 2 diabetic human islets. In conclusion, leucine culture upregulates glucokinase, which increases NAD(P)H level, and ATPSbeta, which increases oxidation of NADH and production of ATP. The combined upregulation of both genes increases glucose-induced cytosolic Ca(2+) and insulin secretion.
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PMID:Leucine regulation of glucokinase and ATP synthase sensitizes glucose-induced insulin secretion in pancreatic beta-cells. 1638 Apr 93

Elevated plasma homocysteine has been reported in individuals with diseases of the metabolic syndrome including vascular disease and insulin resistance. As homocysteine exerts detrimental effects on endothelial and neuronal cells, this study investigated effects of acute homocysteine exposure on beta-cell function and insulin secretion using clonal BRIN-BD11 beta-cells. Acute insulin release studies in the presence of various test reagents were performed using monolayers of BRIN-BD11 cells and samples assayed by insulin radioimmunoassay. Cellular glucose metabolism was assessed by nuclear magnetic resonance (NMR) analysis following 60-min exposure of BRIN-BD11 cell monolayers to glucose in either the absence or presence of homocysteine. Homocysteine dose-dependently inhibited insulin release at moderate and stimulatory glucose concentrations. This inhibitory effect was reversible at all but the highest concentration of homocysteine. 13C-glucose NMR demonstrated decreased labelling of glutamate from glucose at positions C2, C3 and C4, indicating that the tricarboxylic acid (TCA) cycle-dependent glucose metabolism was reduced in the presence of homocysteine. Homocysteine also dose-dependently inhibited insulinotropic responses to a range of glucose-dependent secretagogues including nutrients (alanine, arginine, 2-ketoisocaproate), hormones (glucagon-like peptide-1 (7-36)amide, gastric inhibitory polypeptide and cholecystokinin-8), neurotransmitter (carbachol), drug (tolbutamide) as well as a depolarising concentration of KCl or elevated Ca2+. Insulin secretion induced by activation of adenylate cyclase and protein kinase C pathways with forskolin and phorbol 12-myristate 13-acetate were also inhibited by homocysteine. These effects were not associated with any adverse action on cellular insulin content or cell viability, and there was no increase in apoptosis/necrosis following exposure to homocysteine. These data indicate that homocysteine impairs insulin secretion through alterations in beta-cell glucose metabolism and generation of key stimulus-secretion coupling factors. The participation of homocysteine in possible beta-cell demise merits further investigation.
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PMID:Detrimental actions of metabolic syndrome risk factor, homocysteine, on pancreatic beta-cell glucose metabolism and insulin secretion. 1664 97

The codon 5383-5385 (CCG) in the atpC gene of the unc operon of Escherichia coli cells was replaced with the sequence encoding peptide A of human insulin. The foreign protein fused to the middle part of the gamma-subunit of ATP synthase affects neither biosynthesis of the chimeric polypeptide nor the integration of the EF(0) x F(1) enzyme into the membranes of the E. coli cells. The inserted peptide A does not inhibit the process of oxidative phosphorylation. The ATPase activity of the mutant EF(0) x F(1) enzyme was equal to that of the wild-type enzyme and was regulated by modifiers in the similar way, suggesting that the space in the stalk area of F(0)/F(1) interaction is enough for the introduction of an additional oligopeptide without changing catalytic properties of the ATP synthase.
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PMID:Biochemical characteristics of Escherichia coli ATP synthase with insulin peptide A fused to the globular part of the gamma-subunit. 1700 55

Early and late effects of alloxan diabetes and insulin treatment on mitochondrial membrane structure and function were evaluated by studying the kinetic properties of mitochondrial membrane marker enzyme FoF1-ATPase and its modulation by membrane lipid/phospholipid composition and membrane fluidity. Under all experimental conditions the enzyme displayed three kinetically distinguishable components. In 1 wk-old diabetic animals the enzyme activity was unchanged; however, K(m) and V(max) of component I increased and K(m) of component II decreased. Insulin treatment resulted in lowering of K(m) and V(max) of components II and Ill. One-mon diabetic state resulted in decreased enzyme activity, whereas insulin treatment caused hyperstimulation. K(m) of components I and II decreased together with decreased V(max) of all the components. Insulin treatment restored the K(m) and V(max) values. In late-stage diabetes the catalytic efficiency of components I and II increased; insulin treatment had drastic adverse effect. Binding pattern of ATP was unchanged under all experimental conditions. Diabetic state resulted in progressive decrease in energy of activation in the low temperature range (E(L)). Insulin treatment lowered the energy of activation in the high temperature range (E(H)) without correcting the E(L) values. The phase transition temperatures increased in diabetic state and were not corrected by insulin treatment. Long-term diabetes lowered the total phospholipid content and elevated the cholesterol content; insulin treatment had partial restorative effect. The membrane fluidity decreased in general in diabetic condition and was not corrected by insulin treatment at late stage. Regression analysis studies suggest that specific phospholipid classes and/or their ratios may play a role in modulation of the enzyme activity.
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PMID:Insulin-status-dependent modulation of FoF1-ATPase activity in rat liver mitochondria. 1706 53

Hyperproinsulinemia is observed in type 2 diabetic patients. We hypothesized that the induction of uncoupling protein-2 (UCP2) would impair processing of proinsulin to mature insulin and potentially contribute to hyperproinsulinemia, based on the evidence that hormone processing is an ATP-dependent process and UCP2 up-regulation can suppress cellular ATP production. UCP2 was overexpressed (UCP2-OE) by twofold in INS-1 cells by means of plasmid transfection. Although UCP2-OE reduced glucose-stimulated insulin secretion and cellular ATP content, no effects on proinsulin processing, as measured by western blotting, were observed. To increase the demand for insulin, we then cultured UCP2-OE and control INS-1 cells in medium containing 20 mM KCl for 24 h. High K(+) markedly reduced glucose-stimulated insulin secretion from control cells, indicating inability of cells to meet secretory demand. Independent of UCP2 expression, high K(+) reduced preproinsulin mRNA expression but had no effect on ATP content despite increasing ATP synthase expression. In UCP2-OE cells, high K(+)decreased total cellular insulin species content and increased the ratio of proinsulin to insulin, indicating an impairment of processing. We conclude that UCP2-OE can negatively impact proinsulin processing, possibly by ATP-dependent alteration of the granule environment or reduction of Ca(2+)availability, particularly when cells are chronically stimulated to secrete insulin.
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PMID:Impact of uncoupling protein-2 overexpression on proinsulin processing. 1717 91

Prolonged exposure of beta-cells to high glucose (glucotoxicity) diminishes insulin secretion in response to glucose and has been linked to altered generation of metabolism-secretion coupling factors. We have investigated whether glucotoxicity may also alter calcium handling and late steps in secretion such as exocytosis. Clonal INS-1E beta-cells cultured at high glucose (20 or 30 mM vs. 5.5 mM) for 72 h exhibited elevated basal intracellular calcium ([Ca2+]i), which was KATP-channel dependent and due to long-term activation of protein kinase A. An increased amplitude and shortened duration of depolarization-evoked rises in [Ca2+]i were apparent. These changes were probably linked to the observed increased filling of intracellular stores and to short-term activation of protein kinase A. Insulin secretion was reduced not only by acute stimulation with either glucose or KCl but more importantly by direct calcium stimulation of permeabilized cells. These findings indicate a defect in the final steps of exocytosis. To confirm this, we measured expression levels of some 30 proteins implicated in trafficking/exocytosis of post-Golgi vesicles. Several proteins required for calcium-induced exocytosis of secretory granules were down-regulated, such as the soluble N-ethylmaleimide-sensitive factor-sensitive factor attachment receptor (SNARE) proteins VAMP-2 [vesicle (v)-SNARE, vesicle-associated membrane protein 2] and syntaxin 1 as well as complexin. VAMP-2 was also reduced in human islets. In contrast, cell immunostaining and expression levels of several fluorescent proteins suggested that other post-trans-Golgi trafficking steps and compartments are preserved and that cells were not degranulated. Thus, these studies indicate that, in addition to known metabolic changes, glucotoxicity impedes generation of signals for secretion and diminishes the efficiency of late steps in exocytosis.
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PMID:Glucotoxicity inhibits late steps of insulin exocytosis. 1720 59

Fuel stimulation of insulin secretion from pancreatic beta-cells is thought to be mediated by metabolic coupling factors that are generated by energized mitochondria, including protons, adenine nucleotides, and perhaps certain amino acids (AA), as for instance aspartate, glutamate, or glutamine (Q). The goal of the present study was to evaluate the role of such factors when insulin release (IR) is stimulated by glucose or AA, alone or combined, using (31)P, (23)Na and (1)H NMR technology, respirometry, and biochemical analysis to study the metabolic events that occur in continuously superfused mouse beta-HC9 cells contained in agarose beads and enhanced by the phosphodiesterase inhibitor IBMX. Exposing beta-HC9 cells to high glucose or 3.5 mM of a physiological mixture of 18 AA (AAM) plus 2 mM glutamine caused a marked stimulation of insulin secretion associated with increased oxygen consumption, cAMP release, and phosphorylation potential as evidenced by higher phosphocreatine and lower P(i) peak areas of (31)P NMR spectra. Diazoxide blocked stimulation of IR completely, suggesting involvement of ATP-dependent potassium (K(ATP)) channels in this process. However, levels of MgATP and MgADP concentrations, which regulate channel activity, changed only slowly and little, whereas the rate of insulin release increased fast and very markedly. The involvement of other candidate coupling factors was therefore considered. High glucose or AAM + Q increased pH(i). The availability of temporal pH profiles allowed the precise computation of the phosphate potential (ATP/P(i) x ADP) in fuel-stimulated IR. Intracellular Na+ levels were greatly elevated by AAM + Q. However, glutamine alone or together with 2-amino-2-norbornanecarboxylic acid (which activates glutamate dehydrogenase) decreased beta-cell Na levels. Stimulation of beta-cells by glucose in the presence of AAM + Q (0.5 mM) was associated with rising cellular concentrations of glutamate and glutamine and strikingly lower aspartate levels. Methionine sulfoximine, an inhibitor of glutamine synthetase, blocked the glucose enhancement of AMM + Q-induced IR and associated changes in glutamine and aspartate but did not prevent the accumulation of glutamate. The results of this study demonstrate again that an increased phosphate potential and a functional K(ATP) channel are essential for metabolic coupling during fuel-stimulated insulin release but illustrate that determining the identity and relative importance of all participating coupling factors and second messengers remains a challenge largely unmet.
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PMID:Metabolic and ionic coupling factors in amino acid-stimulated insulin release in pancreatic beta-HC9 cells. 1726 32

In order to better understand the impact of reduced mitochondrial function for the development of insulin resistance and cellular metabolism, human myotubes were established from lean, obese, and T2D subjects and exposed to mitochondrial inhibitors, either affecting the electron transport chain (Antimycin A), the ATP synthase (oligomycin) or respiratory uncoupling (2,4-dinitrophenol). Direct inhibition of the electron transport chain or the ATP synthase was followed by increased glucose uptake and lactate production, reduced glycogen synthesis, reduced lipid and glucose oxidation and unchanged lipid uptake. The metabolic phenotype during respiratory uncoupling resembled the above picture, except for an increase in glucose and palmitate oxidation. Antimycin A and oligomycin treatment induced insulin resistance at the level of glucose and palmitate uptake in all three study groups while, at the level of glycogen synthesis, insulin resistance was only seen in lean myotubes. Primary insulin resistance in diabetic myotubes was significantly worsened at the level of glucose and lipid uptake. The present study is the first convincing data linking functional mitochondrial impairment per se and insulin resistance. Taken together functional mitochondrial impairment could be part of the pathophysiology of insulin resistance in vivo.
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PMID:Insulin resistance and the mitochondrial link. Lessons from cultured human myotubes. 1748 33

Diabetes mellitus is one of the most common genetic diseases that afflicts humans. It is not a single disease but a collection of diseases having in common an abnormal glucose-insulin relationship and a dysfunctional regulation of glucose homeostasis. Of interest is the diabetic state that results when the mitochondrial genome mutates. Epidemiological studies have shown this to occur in humans. Detailed metabolic studies that are impossible to conduct in humans have been carried out in the BHE/Cdb rat. This rat has a mutated mitochondrial ATPase 6 gene. Strategies to ameliorate the consequences of this mutation have been explored and some of the mechanisms for the transcription and translation of the mitochondrial gene product have been elucidated.
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PMID:Linking mitochondrial function to diabetes mellitus: an animal's tale. 1756 52

ATP synthase, or F-ATPase, purified from bovine heart mitochondria in the absence of phospholipids is an assembly of 16 different subunits. In the presence of exogenous phospholipids, two additional hydrophobic proteins, a 6.8kDa proteolipid and diabetes associated protein in insulin sensitive tissue (DAPIT), were associated with the purified complex, with DAPIT at sub-stoichiometric levels. Both proteins are conserved in vertebrates and invertebrates, but not in fungi, and prokaryotic F-ATPases do not contain orthologues of either of them. Therefore, their roles are likely to be peripheral to the synthesis of ATP.
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PMID:Association of two proteolipids of unknown function with ATP synthase from bovine heart mitochondria. 1757 Mar 65


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