Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.6.3.14 (ATP synthase)
7,042 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Widely held theories of the pathogenesis of obesity-associated NIDDM have implicated apparently incompatible events as seminal: 1) insulin resistance in muscle, 2) abnormal secretion of insulin, and 3) increases in intra-abdominal fat. Altered circulating or tissue lipids are characteristic features of obesity and NIDDM. The etiology of these defects is not known. In this perspective, we propose that the same metabolic events, elevated malonyl-CoA and long-chain acyl-CoA (LC-CoA), in various tissues mediate, in part, the pleiotropic alterations characteristic of obesity and NIDDM. We review the evidence in support of the emerging concept that malonyl-CoA and LC-CoA act as metabolic coupling factors in beta-cell signal transduction, linking fuel metabolism to insulin secretion. We suggest that acetyl-CoA carboxylase, which synthesizes malonyl-CoA, a "signal of plenty," and carnitine palmitoyl transferase 1, which is regulated by it, may perform as fuel sensors in the beta-cell, integrating the concentrations of all circulating fuel stimuli in the beta-cell as well as in muscle, liver, and adipose tissue. The target effectors of LC-CoA may include protein kinase C sub-types, complex lipid formation, genes encoding metabolic enzymes or transduction factors, and protein acylation. We support the concept that only under conditions in which both glucose and lipids are plentiful will the metabolic abnormality, which may be termed glucolipoxia, become apparent. If our hypothesis is correct that common signaling abnormalities in the metabolism of malonyl-CoA and LC-CoA contribute to altered insulin release and sensitivity, it offers a novel explanation for the presence of variable combinations of these defects in individuals with differing genetic backgrounds and for the fact that it has been difficult to determine whether one or the other is the primary event.
...
PMID:Are the beta-cell signaling molecules malonyl-CoA and cystolic long-chain acyl-CoA implicated in multiple tissue defects of obesity and NIDDM? 859 30

In recent years, it has become apparent that second messengers and factors other than ATP. metabolically sensitive K+ATP channels and Ca2+ play essential roles in nutrient-induced insulin release. This paper reviews the evidence in support of several new concepts and hypotheses in the field of beta-cell signaling. These include in particular that: a rise in cytosolic Ca2+ is not sufficient to explain the kinetics and extent of secretion induced by glucose; variations in ADP, rather than ATP, regulate beta-cell metabolism and the K+ATP channel; anaplerosis (the replenishment of the citric acid cycle with intermediates) is essential for beta-cell activation: a shift from fatty acid oxidation to esterification is an important event in beta-cell signaling: malonyl-CoA and long chain acyl-CoA esters may act as metabolic coupling factors; glycolytic oscillations underlie, in part, oscillations in electrical activity, cytosolic Ca2+ and insulin release. A metabolic model of fuel sensing that integrates the mode of action of all classes of nutrient secretagogues is proposed.
...
PMID:New insights into pancreatic beta-cell metabolic signaling in insulin secretion. 861 23

31P NMR magnetization transfer measurements have been used to measure the steady state flux between Pi and ATP in yeast cells genetically modified to overexpress an adenine nucleotide translocase isoform. An increase in Pi -> ATP flux and apparent ratio of moles of ATP synthesized/atoms of oxygen consumed (P:O ratio), when these cells were incubated with glucose, demonstrated that the reactions catalyzed by the translocase and F1F0 ATP synthase were readily reversible in vivo. However, when the same cells were incubated with ethanol alone, translocase overexpression had no effect on the measured Pi -> ATP flux or apparent P:O ratio, suggesting that the synthase was now operating irreversibly. This change was accompanied by an increase in the intracellular ADP concentration. These observations are consistent with a model proposed for the kinetic control of mitochondrial ATP synthesis, which was based on isotope exchange measurements with isolated mammalian mitochondria [LaNoue, K. F., Jeffries, F. M. H. & Radda, G. K. (1986) Biochemistry 25, 7667-7675].
...
PMID:31P NMR magnetization transfer study of the control of ATP turnover in Saccharomyces cerevisiae. 869 26

To gain insight into the regulation of pancreatic beta-cell mitochondrial metabolism, the direct effects on respiration of different mitochondrial substrates, variations in the ATP/ADP ratio and free Ca2+ were examined using isolated mitochondria and permeabilized clonal pancreatic beta-cells (HIT). Respiration from pyruvate was high and not influenced by Ca2+ in State 3 or under various redox states and fixed values of the ATP/ADP ratio; nevertheless, high Ca2+ elevated pyridine nucleotide fluorescence, indicating activation of pyruvate dehydrogenase by Ca2+. Furthermore, in the presence of pyruvate, elevated Ca2+ stimulated CO2 production from pyruvate, increased citrate production and efflux from the mitochondria and inhibited CO2 production from palmitate. The latter observation suggests that beta-cell fatty acid oxidation is not regulated exclusively by malonyl-CoA but also by the mitochondrial redox state. alpha-Glycerophosphate (alpha-GP) oxidation was Ca(2+)-dependent with a half-maximal rate observed at around 300 nM Ca2+. We have recently demonstrated that increases in respiration precede increases in Ca2+ in glucose-stimulated clonal pancreatic beta-cells (HIT), indicating that Ca2+ is not responsible for the initial stimulation of respiration [Civelek, Deeney, Kubik, Schultz, Tornheim and Corkey (1996) Biochem. J. 315, 1015-1019]. It is suggested that respiration is stimulated by increased substrate (alpha-GP and pyruvate) supply together with oscillatory increases in ADP [Nilsson, Schultz, Berggren, Corkey and Tornheim (1996) Biochem. J. 314, 91-94]. The rise in Ca2+, which in itself may not significantly increase net respiration, could have the important functions of (1) activating the alpha-GP shuttle, to maintain an oxidized cytosol and high glycolytic flux; (2) activating pyruvate dehydrogenase, and indirectly pyruvate carboxylase, to sustain production of citrate and hence the putative signal coupling factors, malonyl-CoA and acyl-CoA; and (3) increasing mitochondrial redox state to implement the switch from fatty acid to pyruvate oxidation.
...
PMID:Regulation of pancreatic beta-cell mitochondrial metabolism: influence of Ca2+, substrate and ADP. 880 55

Sulphonylurea antidiabetica effectively inhibits the basal hepatic glucose production. Since it has been firmly established that lipophylic sulphonylurea drugs exerted an uncoupling effect on mitochondrial oxidative phosphorylation, a relationship between the reduction of hepatic gluconeogenesis and the insufficient energy supply due to sulphonylureas could be supposed. In this study we have investigated the effects of glibenclamide and gliquidone on mitochondrial bioenergetics in liver after peroral treatments of normal rats with different doses. The treatment of rats with 5 mg/kg glibenclamide or gliquidone daily for 14 days elicited only a marginal inhibition on mitochondrial oxidation capacity and remained without any effect on mitochondrial ATPase activity. Only the supermaximal dose 50 mg/kg for 14 day produced a significant damage in the mitochondrial functions. The basal respiration increased with 60-80 per cent, whereas the ADP- or DNP-stimulated oxygen consumption significantly decreased independently from the respiratory substrates investigated. Similar alterations were found in the mitochondrial ATPase activity after treatment with these drugs. No essential differences have been observed in the actions between glibenclamide and gliquidone. However, the lowest dose applied in this study is many times higher than the usual therapeutic dose. Consequently, glibenclamide and gliquidone do not interact with mitochondrial bioenergetic processes under therapeutic conditions. On the other hand, in different liver and kidney damages we have no sufficient knowledge whether these drugs can be accumulated in these organs and therefore their elevated concentration may interfere with the mitochondrial energy metabolism.
...
PMID:Interference of sulphonylurea antidiabetica with mitochondrial bioenergetics under in vivo conditions. 886 94

Nutrient-stimulated insulin secretion is dependent upon the generation of metabolic coupling factors in the mitochondria of the pancreatic B cell. To investigate the role of Ca2+ in mitochondrial function, insulin secretion from INS-1 cells stably expressing the Ca2+-sensitive photoprotein aequorin in the appropriate compartments was correlated with changes in cytosolic calcium ([Ca2+]c) and mitochondrial calcium ([Ca2+]m). Glucose and KCl, which depolarize the cell membrane, as well as the Ca2+-mobilizing agonist, carbachol (CCh), cause substantial increases in [Ca2+]m which are associated with smaller rises in [Ca2+]c. The L-type Ca2+-channel blocker, SR7037, abolished the effects of glucose and KCl while attenuating the CCh response. Glucose-induced increases in [Ca2+]m, [Ca2+]c, and insulin secretion all demonstrate a pronounced initial peak followed by a sustained plateau. All three parameters are increased synergistically when glucose and CCh are combined. Finally, [Ca2+]m, [Ca2+]c, and insulin secretion also display desensitization phenomena following repeated additions of the three stimuli. The high sensitivity of [Ca2+]m to Ca2+ influx and the desensitization-resensitization effects can be explained by a model in which the mitochondria of INS-1 cells are strategically located to sense Ca2+ influx through plasma membrane Ca2+ channels. In conclusion, the correlation of [Ca2+]m and [Ca2+]c with insulin secretion may indicate a fundamental role for Ca2+ in the adaptation of oxidative metabolism to the generation of metabolic coupling factors and the energy requirements of exocytosis.
...
PMID:Glucose-stimulated insulin secretion correlates with changes in mitochondrial and cytosolic Ca2+ in aequorin-expressing INS-1 cells. 895 15

Glucose metabolism and its relationship with glucose-induced insulin release were studied in beta HC9 and beta TC3 cells to identify and characterize key factors controlling the intermediary metabolism of glucose and glucose-induced insulin release. The beta HC9 cell line, derived from pancreatic islets with beta-cell hyperplasia, is characterized by a normal concentration-dependency curve for glucose-stimulated insulin release, whereas the beta TC3 cell line, derived from pancreatic beta-cell tumors, shows a marked leftward shift of this curve. Maximum velocity and the Michaelis-Menten constant of glucose uptake in beta HC9 and beta TC3 cells were similar, even though GLUT-2 expression in these two cell lines differed. In both cell lines, the kinetic characteristics of glucose usage, glucose oxidation, and glucose-induced oxygen consumption were similar to those of glucose phosphorylation, indicating that the kinetics of glucose metabolism from the glucose phosphorylation step in the cytosol to the mitochondrial process of oxidative phosphorylation are determined by the glucose-phosphorylating enzyme, that is, by glucokinase in beta HC9 cells and by hexokinase in beta TC3 cells. Thus beta HC9 cells provide an opportunity for the quantitative analysis of glucose metabolism, the associated generation of coupling factors, and other essential beta-cell functions involved in glucose sensing and insulin secretion.
...
PMID:Glucose metabolism and insulin release in mouse beta HC9 cells, as model for wild-type pancreatic beta-cells. 896 74

In rat pancreatic islets, D-fructose causes a concentration-related shift to the left of the sigmoidal relationship between insulin release and D-glucose concentration. For instance, when D-fructose is tested at a 80 mM concentration, which is close to the threshold value for stimulation of insulin release by the ketohexose in the absence of D-glucose, a close-to-maximal secretory response is recorded in islets concomitantly exposed to as little as 6.0 to 8.3 mM D-glucose. Under these conditions, however, D-fructose fails to affect the utilization of D-[5-3H]glucose, the oxidation of D-[U-14C]glucose, or its conversion to either 14C-labeled acidic metabolites or amino acids. Under the same experimental conditions, the oxidation of D-[U-14C]fructose and its conversion to 14C-labeled amino acids represent no more than 80-85% of the corresponding values found with 6 mM D-[U-14C]glucose. Actually, the total output of 14CO2 attributable to the oxidation of both D-[U-14C]glucose (6 mM) and D-[U-14C]fructose (80 mM) remains lower than that found in the sole presence of 8.3 mM D-[U-14C]glucose, despite the much higher rate of insulin secretion found in the former compared to the latter situation. These findings suggest that the insulinotropic action of D-fructose cannot be fully accounted for by its capacity to act as a fuel in islet cells, as if it were to involve the generation of a second messenger distinct from those coupling factors currently implied in the process of nutrient-stimulated insulin release.
...
PMID:Hexose metabolism in pancreatic islets: apparent dissociation between the secretory and metabolic effects of D-fructose. 898 42

The knowledge of the mechanism whereby glucose and other fuel stimuli promote the release of insulin by the pancreatic beta cell remains fragmentary. The closure of metabolically sensitive K+ channels and a rise in cytosolic free Ca2+ are key features of beta-cell metabolic signal transduction. However, these two signalling events do not account for the dose dependence of glucose-induced insulin secretion. In fact, recent evidence indicates that there are KATP channel and Ca2+ independent pathway(s) of beta-cell activation which remain to be defined. In this review, we have limited our attention to the recent developments in our understanding of the mode of action of nutrient secretagogues. A particular emphasis is placed in summarising the evidence in support of two new concepts: 1) oscillations in the glycolytic pathway and beta-cell metabolism contribute to the oscillatory nature of beta-cell ionic events and insulin secretion; 2) malonyl-CoA and long chain acyl-CoA esters may act as metabolic coupling factors in beta-cell signalling. Finally, we propose that the altered expression of genes encoding enzymes in the pathway of malonyl-CoA formation and fatty acid oxidation contributes to the beta-cell insensitivity to glucose in some patients with non-insulin-dependent diabetes mellitus.
...
PMID:Signal transduction mechanisms in nutrient-induced insulin secretion. 924 99

Recent acquisitions concerning the physiology, pathology and pharmacology of insulin secretion are reviewed. In terms of physiology, emphasis is placed on new information concerning the role of glucokinase and the identity of coupling factors in the process of glucose-stimulated insulin release. Pathological considerations concern mainly the possible participation of an inherited or acquired defect of FAD-linked mitochondrial glycerophosphate dehydrogenase in the impairment of insulin release in non-insulin-dependent diabetes. Although experimental approaches to correct such a site-specific defect have so far been unsuccessful, new therapeutic tools, especially the esters of certain nutrients, may soon be available for stimulation of proinsulin biosynthesis as well as insulin release in the diseased B cell.
...
PMID:Physiology, pathology and pharmacology of insulin secretion: recent acquisitions. 934 37


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---