共查询到20条相似文献,搜索用时 15 毫秒
1.
Thomas R. Hurd Yvonne Collins Irina Abakumova Edward T. Chouchani Bartlomiej Baranowski Ian M. Fearnley Tracy A. Prime Michael P. Murphy Andrew M. James 《The Journal of biological chemistry》2012,287(42):35153-35160
Reactive oxygen species are byproducts of mitochondrial respiration and thus potential regulators of mitochondrial function. Pyruvate dehydrogenase kinase 2 (PDHK2) inhibits the pyruvate dehydrogenase complex, thereby regulating entry of carbohydrates into the tricarboxylic acid (TCA) cycle. Here we show that PDHK2 activity is inhibited by low levels of hydrogen peroxide (H2O2) generated by the respiratory chain. This occurs via reversible oxidation of cysteine residues 45 and 392 on PDHK2 and results in increased pyruvate dehydrogenase complex activity. H2O2 derives from superoxide (O2˙̄), and we show that conditions that inhibit PDHK2 also inactivate the TCA cycle enzyme, aconitase. These findings suggest that under conditions of high mitochondrial O2˙̄ production, such as may occur under nutrient excess and low ATP demand, the increase in O2˙̄ and H2O2 may provide feedback signals to modulate mitochondrial metabolism. 相似文献
2.
Rodgers Robert L. Christe Michael E. Tremblay George C. Babson John R. Daniels Thomas 《Molecular and cellular biochemistry》2001,226(1-2):97-105
Pharmacologic (millimolar) levels of carnitine have been reported to increase myocardial glucose oxidation, but whether physiologically relevant concentrations of carnitine affect cardiac metabolism is not known. We employed the isolated, perfused rat heart to compare the effects of physiologic levels of carnitine (50 M) and insulin (75 mU/l [0.5 nM]) on the following metabolic processes: (1) glycolysis (release of 3H2O from 5-3H-glucose); (2) oxidation of glucose and pyruvate (production of 14CO2 from U-14C-glucose, 1-14C-glucose, 3,4-14C-glucose, 1-14C-pyruvate, and 2-14C-pyruvate); and (3) oxidation of palmitate (release of 3H2O from 9,10-3H-palmitate). We found that addition of carnitine (50 M) to a perfusate containing both glucose (10 mM) and palmitate (0.5 mM) stimulated glycolytic flux by 20%, nearly doubled the rate of glucose oxidation, and inhibited palmitate oxidation by 20%. These actions of carnitine were uniformly similar to those of insulin. When carnitine and insulin were administered together, their effects on the oxidation of glucose and palmitate, but not on glycolysis, were additive. When pyruvate (1 mM) was substituted for glucose, neither carnitine nor insulin influenced the rate of oxidation of pyruvate or palmitate. In combination, however, carnitine and insulin sharply suppressed pyruvate oxidation (75%) and doubled the rate of palmitate oxidation. None of the responses to carnitine or insulin was affected by varying the isotopic labeling of glucose or pyruvate. The results show that carnitine, at normal blood levels, exerts insulin-like effects on myocardial fuel utilization. They also suggest that plasma carnitine in vivo may interact with insulin both additively and permissively on the metabolism of carbohydrates and fatty acids 相似文献
3.
A class of ω-aminoalkyl glycosides previously found to antagonize insulin's action on glucose oxidation in fat cells and to stimulate glucose oxidation in insulin's absence is now shown to mimic insulin also on the conversion of glucose to free fatty acids and to glycerol and glycerides. These glycosides also act like insulin by inhibiting hormone- and cholera toxin-stimulated lipolysis. Various lines of evidence demonstrate that most, if not all, of the insulin-like activity of these glycosides results from H2O2 formed from an amine oxidase-catalyzed oxidation of the aminoalkyl moiety of these compounds. A contaminant in the bovine plasma albumin (BPA) preparations used in the bioassays was found to represent a major source of the amine oxidase activity. Membrane (ghost) preparations were also found to possess amine oxidase activity capable of forming H2O2 from the glycosides in amounts sufficient to express insulin-like activity. Preliminary experiments with intact adipocytes suggest that this activity is located on the cell surface. The BPA-associated activity corresponds to the known Cu2+-containing “plasma-type” amine oxidase (EC 1.4.3.6) on the basis of its substrate specificity and susceptibility to selective inhibitors. The plasma membrane activity appears to correspond to neither the plasma-type nor to the flavin-containing mitochondrial-type (EC 1.4.3.4) and remains to be identified. The observed potent antilipolytic effects of both H2O2 and the aminoalkyl glycosides points out that any mechanism used to explain the insulin-like action of H2O2 must account for this ability to inhibit lipolysis as well as to stimulate glucose utilization. That catalase inhibits the insulin-like action of the glycosides and H2O2, but not that of insulin indicates that insulin's action is not mediated by cell surface-produced H2O2. Also, since the insulin antagonistic activity of these glycosides was not inhibited by catalase, H2O2 formation is not responsible for this antagonism. The latter finding, added to present and previous evidence on the carbohydrate structural requirements involved in H2O2 production and in the insulin-like biological and binding properties of the aminoalkyl glycosides, is consistent with a role(s) for their carbohydrate moieties in both the insulin antagonistic and agonistic activities of these compounds. 相似文献
4.
Maggie K. Diamond-Stanic Elizabeth M. Marchionne Mary K. Teachey David E. Durazo John S. Kim Erik J. Henriksen 《Biochemical and biophysical research communications》2011,(3):2645
Increased cellular exposure to oxidants may contribute to the development of insulin resistance and type 2 diabetes. Skeletal muscle is the primary site of insulin-dependent glucose disposal in the body; however, the effects of oxidative stress on insulin signaling and glucose transport activity in mammalian skeletal muscle are not well understood. We therefore studied the effects of a low-level in vitro oxidant stress (30–40 μM H2O2) on basal and insulin-stimulated (5 mU/ml) glucose transport activity and insulin signaling at 2, 4, and 6 h in isolated rat soleus muscle. H2O2 increased basal glucose transport activity at 2 and 4 h, but not at 6 h. This low-level oxidant stress significantly impaired insulin-stimulated glucose transport activity at all time points, and was associated with inhibition of insulin-stimulated phosphorylation of Akt Ser473 and GSK-3β Ser9. In the presence of insulin, H2O2 decreased total protein expression of IRS-1 at 6 h and IRS-2 at 4 and 6 h. Phosphorylation of p38 MAPK Thr180/Tyr182 was transiently increased by H2O2 in the presence and absence of insulin at 2 and 4 h, but not at 6 h. Selective inhibition of p38 MAPK with A304000 partially rescued the H2O2-induced reduction in insulin-stimulated glucose transport activity. These results indicate that direct in vitro exposure of isolated mammalian skeletal muscle to a low-level oxidant stress impairs distal insulin signaling and insulin-stimulated glucose transport activity, at least in part, due to a p38 MAPK-dependent mechanism. 相似文献
5.
Insulin, a hypoglycemic hormone, has multiple functions in the brain. The aim of this study to identify the mechanisms of insulin in hydrogen peroxide (H2O2)-induced toxicity in the C6 glial cells. Cytotoxicity, lactate dehydrogenase, nitric oxide, reactive oxygen species and calcium ion, lipid peroxidation, protein oxidation and glutathione levels were determined. Signaling pathway molecules were assessed by western blotting and RT-PCR. The results showed that treatment with insulin reduced the cell death and cell membrane damages against H2O2-induced toxicity. Furthermore, insulin interfered H2O2-induced intracellular generation of reactive oxygen species and calcium-ion transport, apoptosis, including lipid and protein oxidation products. Cells treated with insulin reverted H2O2-induced suppression of reduced glutathione levels by blocking oxidized glutathione. Moreover, insulin treatment activates Akt, restores ERK1/2 and Bcl-2 by preventing Bax and Bax/Bcl-2 ratio. Our results suggest that treatment of insulin exerts potential role against 24?h of H2O2-induced toxicity in C6 cells. 相似文献
6.
Formation and Conversion of Oxygen Metabolites by Lactococcus lactis subsp. lactis ATCC 19435 under Different Growth Conditions 总被引:2,自引:0,他引:2
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A semidefined medium based on Casamino Acids allowed Lactococcus lactis ATCC 19435 to grow in the presence of oxygen at a slow rate (0.015 h−1). Accumulation of H2O2 in the culture prevented a higher growth rate. Addition of asparagine to the medium increased the growth rate, whereby H2O2 accumulated only temporarily during the lag phase. H2O2 is an inhibitor for several glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase being the most sensitive. Strain ATCC 19435 contained NADH oxidase (maximum specific rate under aerobic conditions, 426 nmol of NADH min−1 mg of protein−1), which reduced oxygen to water, whereby superoxide was formed as a by-product. H2O2 originated from the dismutation of superoxide by superoxide dismutase. Although H2O2 was rapidly destroyed under high metabolic fluxes, neither NADH peroxidase nor any other enzymatic H2O2-reducing activity was detected. However, pyruvate, the end product of glycolysis, reacted nonenzymatically and rapidly with H2O2 and hence was a potential alternative for scavenging of this oxygen metabolite intracellularly. Indeed, intracellular concentrations of up to 93 mM pyruvate were detected in aerobic cultures growing at high rates. It is hypothesized that self-generated pyruvate may serve to protect L. lactis strain ATCC 19435 from H2O2. 相似文献
7.
Lignin synthesis: The generation of hydrogen peroxide and superoxide by horseradish peroxidase and its stimulation by manganese (II) and phenols 总被引:3,自引:0,他引:3
Barry Halliwell 《Planta》1978,140(1):81-88
The enzyme horseradish peroxidase (EC 1.11.1.7) catalyses oxidation of NADH. NADH oxidation is prevented by addition of the enzyme superoxide dismutase (EC 1.15.1.1) to the reaction mixture before adding peroxidase but addition of dismutase after peroxidase has little inhibitory effect. Catalase (EC 1.11.1.6) inhibits peroxidase-catalysed NADH oxidation when added at any time during the reaction. Apparently the peroxidase uses hydrogen peroxide (H2O2) generated by non-enzymic breakdown of NADH to catalyse oxidation of NADH to a free-radical, NAD., which reduces oxygen to the superoxide free-radical ion, O2
.-. Some of the O2
.- reacts with peroxidase to give peroxidase compound III, which is catalytically inactive in NADH oxidation. The remaining O2
.- undergoes dismutation to O2 and H2O2. O2
.- does not react with NADH at significant rates. Mn2+ or lactate dehydrogenase stimulate NADH oxidation by peroxidase because they mediate a reaction between O2
.- and NADH. 2,4-Dichlorophenol, p-cresol and 4-hydroxycinnamic acid stimulate NADH oxidation by peroxidase, probably by breaking down compound III and so increasing the amount of active peroxidase in the reaction mixture. Oxidation in the presence of these phenols is greatly increased by adding H2O2. The rate of NADH oxidation by peroxidase is greatest in the presence of both Mn2+ and those phenols which interact with compound III. Both O2
.- and H2O2 are involved in this oxidation, which plays an important role in lignin synthesis. 相似文献
8.
Washed cells of Desulfovibrio vulgaris strain Marburg oxidized H2, formate, lactate or pyruvate with sulfate, sulfite, trithionate, thiosulfate or oxygen as electron acceptor. CuCl2 as an inhibitor of periplasmic hydrogenase inhibited H2 and formate oxidation with sulfur compounds, and lactate oxidation in H2-grown, but not in lactate-grown cells. H2 oxidation was sensitive to O2 concentrations above 2% saturation. Carbon monoxide inhibited the oxidation of all substrates tested. Additions of micromolar H2 pulses to cells incubated in KCl in the presence of various sulfur compounds (reductant pulse method) resulted in a reversible acidification. This proton release was stimulated by thiocyanate, methyl triphenylphosphonium (MTPP+) or valinomycin plus EDTA, and completely inhibited by the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP), CuCl2 or carbon monoxide. The extrapolated H+/H2 ratios obtained with sulfate, sulfite, trithionate or thiosulfate varied from 1.0 to 1.7. Micromolar additions of O2 to cells incubated in the presence of excess of electron donor (oxidant pulse method) caused proton translocation with extrapolated H+/H2 ratios of 3.9 with H2, 1.6 with lactate and 2.4 with pyruvate. Since a periplasmic hydrogenase can release at maximum 2 H+/H2, it is concluded that D. vulgaris is able to generate a proton gradient by vectorial proton translocation across the cytoplasmic membrane and by extracellular proton release by a periplasmic hydrogenase. 相似文献
9.
Two strains of Lactobacillus plantarum accumulated H2O2 when grown aerobically in a complex glucose based medium. The H2O2 accumulation did not occur immediately on exposure of the culture to O2 but was delayed for a time which, in the case of one strain, was dependent on the amount of inoculum used to seed the culture. The accumulation was always preceded by an increase in the rate of O2 utilization by the cultures. The latter coincided approximately with an increase in specific activity of NADH oxidase, pyruvate oxidase and NADH peroxidase. H2O2 was not a product of NADH oxidase in vitro but was formed in substantial quantities from O2 during oxidation of pyruvate. The three enzymes were induced by O2 and H2O2; the induction of NADH oxidase responded to lower levels of O2 (but not of H2O2) than the pyruvate oxidase or the NADH peroxidase.Abbreviations MRSG
Mann, Rogosa and Sharpe medium (1960) with glucose as fermentation source
- TPP
thiamin pyrophosphate 相似文献
10.
W J Malaisse S Kawazu A Herchuelz J C Hutton G Somers G Devis A Sener 《Archives of biochemistry and biophysics》1979,194(1):49-62
In isolated rat pancreatic islets, exogenous l-lactate causes a dose-related enhancement of glucose-induced insulin release and shifts the sigmoidal curve relating insulin output to ambient glucose concentrations to the left. l-Lactate also enhances α-ketoisocaproate-induced insulin release and glucose-induced proinsulin biosynthesis. l-Lactate rapidly accumulates in the islet cells, is converted to pyruvate and CO2, and raises the intracellular concentration of both ATP and NAD(P)H. On a molar basis, the insulinotropic capacity of nutrients ranges as follows d-glucose ? l-lactate > pyruvate = d/l-lactate > d-lactate and does not correlate with their respective oxidation rates. However, when allowance is made for the intracellular interconversion of these exogenous nutrients, for their reciprocal influence upon oxidation rates, and for their sparing action on the utilization of endogenous fuels, a close correlation is found between the aptitude of glucose, l-lactate, and pyruvate to generate reducing equivalents and to stimulate insulin release. It is proposed that the concentration of NAD(P)H in islet cells affects the ionophoretic fluxes of cations (K+, Ca2+) across membrane systems and, hence, regulates the net uptake of Ca2+ and subsequent release of insulin. The effect of l-lactate upon Ca2+ handling is sufficiently rapid to account for the immediate secretory response to this nutrient. 相似文献
11.
Dehydrogenases that use ubiquinone as an electron acceptor, including complex I of the respiratory chain, complex II, and glycerol-3-phosphate dehydrogenase, are known to be direct generators of superoxide and/or H2O2. Dihydroorotate dehydrogenase oxidizes dihydroorotate to orotate and reduces ubiquinone to ubiquinol during pyrimidine metabolism, but it is unclear whether it produces superoxide and/or H2O2 directly or does so only indirectly from other sites in the electron transport chain. Using mitochondria isolated from rat skeletal muscle we establish that dihydroorotate oxidation leads to superoxide/H2O2 production at a fairly high rate of about 300 pmol H2O2·min−1·mg protein−1 when oxidation of ubiquinol is prevented and complex II is uninhibited. This H2O2 production is abolished by brequinar or leflunomide, known inhibitors of dihydroorotate dehydrogenase. Eighty percent of this rate is indirect, originating from site IIF of complex II, because it can be prevented by malonate or atpenin A5, inhibitors of complex II. In the presence of inhibitors of all known sites of superoxide/H2O2 production (rotenone to inhibit sites in complex I (site IQ and, indirectly, site IF), myxothiazol to inhibit site IIIQo in complex III, and malonate plus atpenin A5 to inhibit site IIF in complex II), dihydroorotate dehydrogenase generates superoxide/H2O2, at a small but significant rate (23 pmol H2O2·min−1·mg protein−1), from the ubiquinone-binding site. We conclude that dihydroorotate dehydrogenase can generate superoxide and/or H2O2 directly at low rates and is also capable of indirect production at higher rates from other sites through its ability to reduce the ubiquinone pool. 相似文献
12.
An oxidase activity utilizing reduced nicotinamide adenine dinucleotide phosphate (NADPH) and producing H2O2 was observed in intact adipocytes of rat, as well as in the isolated plasma membranes of these cells. A stoichiometry of 1 mol of H2O2 production per mole of NADPH disappearance was found with isolated plasma membranes. Activation of this enzyme (R) was produced by pretreatment of cells with insulin, dithiothreitol, or sulfhydryl inhibitors, e.g., p-chloromercuribenzoate or tosyl-l-lysine chloromethyl ketone. All of these agents also stimulated glucose oxidation via the hexose monophosphate shunt. Activation of R was also observed with biologically active derivatives of insulin, e.g., proinsulin or desalanine insulin, but not with an inactive derivative, desoctapeptide insulin. The enzyme could not be activated by exposing the cells to membrane perturbants, e.g., hypotonic conditions or Triton X-100 (0.01–0.1%). The enzyme activity in the plasma membrane had a pH optimum at 6.0 and, from the Lineweaver-Burke plot, V was determined at 230 nmol and Km for NADPH was at 5.8 × 10?5, m. The activity remained unaltered in the presence of sodium azide or cyanide. Preincubation of adipocytes with insulin or SH reagents or direct addition of oxidants, e.g., H2O2, potassium ferricyanide, or phenazine methosulfate, to the membranes also caused inhibition of adenylate cyclase (AC). This enzyme activity could be restored in these preparations by adding thiols. It is suggested that inhibition of AC in whole cells in response to insulin may be caused by oxidation of its SH groups by the H2O2 generated from the activated NADPH oxidase. Reversal of this inhibition may involve cellular reducing equivalents. The evidence suggests that the plasma membrane enzymes, i.e., NADPH oxidase and adenylate cyclase, are controlled, in part, by the intracellular redox potential. 相似文献
13.
《Journal of receptor and signal transduction research》2013,33(3):212-220
AbstractExogenous hydrogen peroxide (H2O2) can easily penetrate into biological membranes and enhance the formation of other reactive oxygen species (ROS). In the present study, we have investigated the neuroprotective effects of insulin on H2O2-induced toxicity of retinoic acid (RA)-differentiated SH-SY5Y cells. To measure the changes in the cell viability of SH-SY5Y cells at different concentrations of H2O2 for 24?h, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT)-based assay was used and a 100?µM H2O2 was selected to establish a model of H2O2-induced oxidative stress. Further assays showed that 24?h of 100?µM H2O2-induced significant changes in the levels of lactate dehydrogenase (LDH), nitric oxide (NO), ROS, and calcium ion (Ca2+) in neuronal cells, but insulin can effectively diminish the H2O2-induced oxidative damages to these cells. Moreover, cells treated with insulin increased H2O2-induced suppression of glutathione levels and exerted an apparent suppressive effect on oxidative products. The results of insulin treatment with SH-SY5Y cells increased the Bcl-2 levels and decreased the Akt levels. The treatment of insulin had played a protective effect on H2O2-induced oxidative stress related to the Akt/Bcl-2 pathways. 相似文献
14.
Dichloroacetate has effects upon hepatic metabolism which are profoundly different from its effects on heart, skeletal muscle, and adipose tissue metabolism. With hepatocytes prepared from meal-fed rats, dichloroacetate was found to activate pyruvate dehydrogenase, to increase the utilization of lactate and pyruvate without effecting an increase in the net utilization of glucose, to increase the rate of fatty acid synthesis, and to decrease slightly [1-14C]oleate oxidation to 14CO2 without decreasing ketone body formation. With hepatocytes isolated from 48-h-starved rats, dichloroacetate was found to activate pyruvate dehydrogenase, to have no influence on net glucose utilization, to inhibit gluconeogenesis slightly with lactate as substrate, and to stimulate gluconeogenesis significantly with alanine as substrate. The stimulation of fatty acid synthesis by dichloroacetate suggests that the activity of pyruvate dehydrogenase can be rate determining for fatty acid synthesis in isolated liver cells. The minor effects of dichloroacetate on gluconeogenesis suggest that the regulation of pyruvate dehydrogenase is only of marginal importance in the control of gluconeogenesis. 相似文献
15.
Reactive oxygen species (ROS) released from polymorphonuclear leukocytes and macrophages could cause DNA damage, but also induce cell death. Therefore inhibition of cell death must be an important issue for accumulation of genetic changes in lymphoid cells in inflammatory foci. Scavengers in the post culture medium of four lymphoid cell lines, lymphoblastoid cell lines (LCL), Raji, BJAB and Jurkat cells, were examined. Over 80% of cultured cells showed cell death 24 h after xanthine (X)/xanthine oxidase (XOD) treatment, which was suppressed by addition of post culture medium from four cell lines in a dose-dependent manner. H2O2 but not O·-2 produced by the X/XOD reaction was responsible for the cytotoxity, thus we used H2O2 as ROS stress thereafter. The H2O2-scavenging activity of post culture media from four cell lines increased rapidly at the first day and continued to increase in the following 2–3 days for LCL, Raji and BJAB cells. The scavenging substance was shown to be pyruvate, with various concentrations in the cultured medium among cell lines. Over 99% of total pyruvate was present in the extracellular media and less than 1% in cells. α-Cyano-4-hydroxycinnamate, a specific inhibitor of the H+-monocarbohydrate transporter, increased the H2O2-scavenging activity in the media from all four cell lines via inhibition of pyruvate re-uptake by cultured cells from the media. These findings suggest that lymphoid cells in inflammatory foci could survive even under ROS by producing pyruvate, so that accumulation of lymphoid cells with DNA damage is possible. 相似文献
16.
《Free radical research》2013,47(3):347-356
AbstractOxidative stress is induced by excess accumulation of reactive oxygen and nitrogen species (RONS). Astrocytes are metabolically active cells in the brain and understanding astrocytic responses to oxidative stress is essential to understand brain pathologies. In addition to direct oxidative stress, exogenous hydrogen peroxide (H2O2) can penetrate biological membranes and enhance formation of other RONS. The present study was carried out to examine the role of insulin in H2O2-induced oxidative stress in rat astrocytic cells. To measure changes in the viability of astrocytes at different concentrations of H2O2 for 3 h, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT)-based assay was used and 500 μM H2O2 was selected to establish a model of H2O2-induced oxidative stress. Further assays showed that 3 h of 500 μM H2O2-induced significant changes in the levels of lactate dehydrogenase (LDH), reactive oxygen species (ROS) and calcium ion (Ca2+) in C6 cells, with insulin able to effectively diminish H2O2-induced oxidative damage to C6 cells. Western blotting studies showed that insulin treatment of astrocytes increased the levels of phosphorylated Akt and magnified the decrease in total Bcl-2 protein. The protective effect of insulin treatment on H2O2-induced oxidative stress in astrocytes by reducing apoptosis may relate to the PI3K/Akt pathway. 相似文献
17.
The abilities of insulin and the insulin mimickers spermine and H2O2 to stimulate 3-O-methyl glucose transport in isolated rat ft cells were stuided in an attempt to determine possible common mechanisms of action. All three agents caused a seven- to 12-fold stimulation of initial rates of glucose transport with insulin being the most effective agent. Insulin and spermine displayed similar time courses for the onset of their stimulation of transport; an initial lag before any effect was seen and then a gradual rise until the full effect was reached. The time course of H2O2 activation of glucose transport was different since stimulation was seen at the earliest time point tested and then gradually rose to the maximal effect. Trypsinization of cells removed insulin receptors and rendered the cells insensitive to insulin but not to spermine or H2O2. However, trypsinization did alter the time course of H2O2 action, causing an initial lag phase to appear and a general slowing of the activation kinetics. Pretreatment of cells with 2,4-dinitrophenol to lower ATP levels prevented the stimulatory effects of insulin and the mimickers. All three of the agents revealed a similar temperature dependency for stimulated glucose transport, resulting in linear Arrhenius plots with activation energies of 10.2–11.4 kcal/mole. These results show that (1) H2O2 does not act directly on the glucose transport system of rat adipocytes and (2) insulin and H2O most likely act through a common energy-dependent biochemical pathway to stimulate glucose transport, but H2O2 enters the stimulus-response sequence distal to the initial steps in insulin action. 相似文献
18.
J. Pesquero J. L. Albi M. A. Gallardo J. Planas J. Sánchez 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(5):448-454
Summary Glucose metabolism has been studied in Salmo trutta red blood cells. From non-metabolizable analogue (3-O-methyl glucose and l-glucose) uptake experiments it is concluded that there is no counterpart to the membrane transport system for glucose found in mammalian red blood cells. Once within the cells, glucose is directed to CO2 and lactate formation through both the Embden-Meyerhoff and hexose monophosphate shunts; lactate appears as the most important endproduct of glucose metabolism in these cells. From experiments under anaerobic conditions, and in the presence of an inhibitor of pyruvate transfer to mitochondria, most of the CO2 formed appears to derive from the hexose monophosphate pathway. Appreciable O2 consumption has been detected, but there is no clear relationship between this and substrate metabolism. Key enzymes of glucose metabolism hexokinase, fructose-6-phosphate kinase and, probably, pyruvate kinase are out of equilibrium, confirming their regulatory activity in Salmo trutta red blood cells. The presence of isoproterenol, a catecholamine analogue, induces important changes in glucose metabolism under both aerobic and anaerobic conditions, and increases the production of both CO2 and lactate. From the data presented, glucose appears to be the major fuel for Salmo trutta red blood cells, showing a slightly different pattern of glucose metabolism from rainbow trout red blood cells.Abbreviations EM
Embden-Meyerhoff pathway
- G6D
glucose-6-phosphate dehydrogenase
- GOT
glutamate oxalacetate transaminase
- GPI
glucose phosphate isomerase
- HK
hexokinase
- HMS
hexose monophosphate shunt
- IP
isoproterenol
- LDH
lactate dehydrogenase
- MCB
modified Cortland buffer
- OMG
3-O-methyl glucose
- PFK
fructose-6-phosphate kinase
- PK
pyruvate kinase
- RBC
red blood cells
- TAC
tricarboxylic acid cycle 相似文献
19.
Maternal hypoxia is associated with a decrease in left ventricular capillary density while cardiac performance is preserved, implying a mismatch between metabolism and diffusive exchange. We hypothesised this requires a switch in substrate metabolism to maximise efficiency of ATP production from limited oxygen availability. Rat pups from pregnant females exposed to hypoxia (FIO2=0.12) at days 10-20 of pregnancy were grown to adulthood and working hearts perfused ex vivo. 14C-labelled glucose and 3H-palmitate were provided as substrates and metabolism quantified from recovery of 14CO2 and 3H2O, respectively. Hearts of male offspring subjected to Maternal Hypoxia showed a 20% decrease in cardiac output (P<0.05), despite recording a 2-fold increase in glucose oxidation (P<0.01) and 2.5-fold increase (P<0.01) in palmitate oxidation. Addition of insulin to Maternal Hypoxic hearts, further increased glucose oxidation (P<0.01) and suppressed palmitate oxidation (P<0.05), suggesting preservation in insulin signalling in the heart. In vitro enzyme activity measurements showed that Maternal Hypoxia increased both total and the active component of cardiac pyruvate dehydrogenase (both P<0.01), although pyruvate dehydrogenase sensitivity to insulin was lost (NS), while citrate synthase activity declined by 30% (P<0.001) and acetyl-CoA carboxylase activity was unchanged by Maternal Hypoxia, indicating realignment of the metabolic machinery to optimise oxygen utilisation. Capillary density was quantified and oxygen diffusion characteristics examined, with calculated capillary domain area increased by 30% (P<0.001). Calculated metabolic efficiency decreased 4-fold (P<0.01) for Maternal Hypoxia hearts. Paradoxically, the decline in citrate synthase activity and increased metabolism suggest that the scope of individual mitochondria had declined, rendering the myocardium potentially more sensitive to metabolic stress. However, decreasing citrate synthase may be essential to preserve local PO2, minimising regions of hypoxia and hence maximising the area of myocardium able to preserve cardiac output following maternal hypoxia. 相似文献
20.
Regulation of lipogenesis in adipose tissue: the significance of the activation of pyruvate dehydrogenase by insulin 总被引:3,自引:0,他引:3
Simultaneous measurements were made of lipogenesis and pyruvate dehydrogenase activity in segments of rat epididymal adipose tissue incubated with saturating amounts of [U-14C]glucose and insulin. Glucose was converted to fatty acids at a rate only 64–79% of that permitted by the tissue's content of the active form of pyruvate dehydrogenase (PDHa). Addition of either of the electron acceptors, phenazine methosulfate (10 μm) or N,N,N′,N′-tetramethyl-p-phenylenediamine (50 μm), increased lipogenesis until it equalled the PDHa activity of the tissue. Pyruvate release was increased 2-fold or more by the electron acceptors, suggesting that the increase in lipogenesis might have resulted from an increase in the intracellular pyruvate levels such that PDHa became saturated with substrate. Higher levels of the electron acceptors decreased PDHa activity, and reduced lipogenesis correspondingly. The data suggest that the maximal rate of lipogenesis in the presence of glucose and insulin is limited by the inability of the tissue to elevate pyruvate levels sufficiently to saturate PDHa. Although glycerol release was increased by either electron acceptor and insulin partially overcame this effect, the effects of the electron acceptors on PDHa activity could not be attributed to an increase in lipolysis. 相似文献