Decrease In Energy Charge Research Articles

Abstract Tu113: Metabolomic Profile of Human End-Stage Ischemic Cardiomyopathy Reveals Few Differences from Non-Ischemic Cardiomyopathy

Background: The heart is highly metabolic, relying on a range of fuels to sustain its high generation of ATP. The primary source of energy in the human heart is fatty acids, but fatty acid oxidation is reduced in failing hearts, contributing to a decrease in ATP production. Previously, we provided a comprehensive metabolic profile of human non-ischemic cardiomyopathy (NICM) hearts, including maintained ATP levels despite decreased energy charge (EC), lower acylcarnitines, acyl CoAs, and free fatty acids, suggesting a defect in fatty acid import. Research Questions: The pathogenesis of ischemic cardiomyopathy (ICM) is dramatically different from that of NICM, raising the question of whether metabolic defects differ between these two conditions. Aims: Our current study was therefore aimed at elucidating the metabolomic profile of end-stage ICM compared to that of NICM. Methods: Whole human hearts were obtained either from patients with end-stage heart failure (NICM or ICM) undergoing cardiac transplantation or from brain-dead organ donors. Hearts were arrested in situ and kept in ice-cold cardioplegia solution at all times. Transmural tissue samples were obtained from left ventricular free wall, snap frozen, and extracted metabolites were quantified by liquid chromatography coupled with mass spectrometer. Results: The comparison of metabolomics data from non-failing (NF) control heart samples and NICM samples were consistent with our previous study, with marked decrease in acylcarnitines and increase in lysophosphatidylcholine. On the other hand, the metabolomics profiles of ICM and NICM samples were remarkably similar. Phenylacetylglutamine and trimethylamine N-oxide, both related to atherosclerotic disease risk, were statistically significantly higher in ICM samples compared to NICM samples. Conclusion(s): The human cardiac metabolome of end-stage ICM is nearly identical to that of NICM, despite dramatically different pathogeneses, suggesting that end-stage heart failure constitutes a final common pathway. It would be of great interest to evaluate metabolomic profiles of the diseases differ at earlier timepoints.

The metabolism of nonstructural carbohydrates, lipids, and energy in two Cycas species with differential tolerance to unexpected freezing stress.

With the climate warming, the occurrence of freezing events is projected to increase in late spring and early autumn in the Northern Hemisphere. Observation of morphological traits showed that Cycas panzhihuaensis was more tolerant to unexpected freezing stress than C. bifida. Energy balance is crucial for plant tolerance to stress. Here, we aimed to determine whether the different responses of the two species to the unpredicted freezing stress were associated with the metabolism of energy and related substances. The effects of unexpected freezing temperatures on C. panzhihuaensis and C. bifida were studied by measuring chlorophyll fluorescence parameters, energy charge and the profile of nonstructural carbohydrates (NSC) and lipids. C. panzhihuaensis exhibited higher stability of photosynthetic machinery than C. bifida under unpredicted freezing events. Significant interaction between species and treatments were observed in the energy charge, the level of NSC and its most components and the amount of most lipid categories and lipid classes. The decrease of soluble sugar and the increase of neutral glycerolipids at the early freezing stage, the accumulation of membrane glycerolipids at the late freezing stage and the continuous decrease of energy charge during the freezing period were the characteristics of C. panzhihuaensis responding to unexpected freezing stress. The degradation of membrane glycerolipids and the continuous decrease of soluble sugar during the freezing period and the accumulation of neutral glycerolipids and energy charge at the late freezing stage represented the characteristics of C. bifida responses. The different freezing sensitivity between C. panzhihuaensis and C. bifida might be associated with the differential patterns of the metabolism of energy, NSC and lipids. C. panzhihuaensis possesses the potential to be introduced to the areas of higher latitudes and altitudes.

Fucoidan treatment alleviates chilling injury in cucumber by regulating ROS homeostasis and energy metabolism.

Chilling injury is a major hindrance to cucumber fruit quality during cold storage. In this study, we evaluated the effects of fucoidan on fruit quality, reactive oxygen species homeostasis, and energy metabolism in cucumbers during cold storage. The results showed that, compared with the control cucumber fruit, fucoidan-treated cucumber fruit exhibited a lower chilling injury index and less weight loss, as well as reduced electrolyte leakage and malondialdehyde content. The most pronounced effects were observed following treatment with fucoidan at 15 g/L, which resulted in increased 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radical scavenging rates and reduced superoxide anion production rate and hydrogen peroxide content. The expression and activity levels of peroxidase, catalase, and superoxide dismutase were enhanced by fucoidan treatment. Further, fucoidan treatment maintained high levels of ascorbic acid and glutathione, and high ratios of ascorbic acid/dehydroascorbate and glutathione/oxidized glutathione. Moreover, fucoidan treatment increased the activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and their gene expression. Fucoidan treatment significantly delayed the decrease in ATP and ADP, while preventing an increase in AMP content. Finally, fucoidan treatment delayed the decrease of energy charge and the activities and gene expression of H+-ATPase, Ca2+-ATPase, cytochrome c oxidase, and succinate dehydrogenase in cucumber fruits. Altogether, our findings indicate that fucoidan can effectively enhance antioxidant capacity and maintain energy metabolism, thereby improving cucumber cold resistance during cold storage.

Exogenous ATP attenuated fermentative metabolism in postharvest strawberry fruit under elevated CO2 atmosphere by maintaining energy status

Elevated CO2 shows adverse effects in horticultural crops including off-flavor formation and carbohydrate consumption. Here, 1 mM adenosine triphosphate (ATP) was applied to strawberry fruit under 20 % CO2 atmosphere to investigate its regulation on fermentative and carbohydrate metabolism. The results showed that ATP treatment increased endogenous ATP content by 27 %, and delayed the decrease of energy charge under elevated CO2 atmosphere. Exogenous ATP showed no adverse effects on fruit firmness and color but attenuated the accumulation of acetaldehyde and ethanol, which were 72 % and 75 % lower in ATP+CO2-treated fruit compared CO2-treared fruit, respectively. The inhibition of fermentative metabolism resulted from the repression of pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) activities, as well as FaADH expression. Meanwhile, ATP treatment also maintained carbohydrate levels under elevated CO2 atmosphere, with 6 %, 7 %, and 11 % more glucose, fructose and sucrose observed at the end of the storage period as compared with the CO2-treated group, respectively. The down-regulation of enzymes activities and gene expressions involved in sucrose catabolism and glycolysis may account for the inhibition of carbohydrate consumption. These results indicated that exogenous ATP might be a strategy to optimize elevated CO2 treatment to avoid its adverse effects.

Roles of adenosine monophosphate activated protein kinase in skeletal muscle atrophy in rats with severe scald

Objective: To investigate the expression and phosphorylation level change of adenosine monophosphate activated protein kinase (AMPK) in skeletal muscle of severely scald rats and its roles in skeletal muscle atrophy in severely scalded rats. Methods: The experimental research method was applied. Totally 100 6-week-old male Wistar rats were divided into sham injury group and scald group according to the random number table, with 50 rats in each group. After weighing the body weight, rats in scald group were inflicted with full-thickness scald of 30% total body surface area on the back, and rats in sham injury group were simulated with scald. At 6 h and on 1, 3, 5, and 7 d post injury, 10 rats in each group were taken to measure their body weights and weights of extensor digitorum longus and soleus muscle. At 6 h and on 1, 3, 5, and 7 d post injury, the tibialis anterior muscles were collected, the mRNA expressions of muscle atrophy F-box protein (MAFbx) and muscle-specific RING finger protein 1 (MuRF1) were detected by real-time fluorescent quantitative reverse transcription polymerase chain reaction; the content of adenosine monophosphate (AMP), adenosine diphosphate, and adenosine triphosphate (ATP) were detected by high performance liquid chromatography, and AMP/ATP ratio and energy charge were calculated; the protein expressions of AMPK-α and phosphorylated AMPK-α (p-AMPK-α) were detected by Western blotting, and the p-AMPK-α/AMPK-α ratio was calculated, with sample number of 4 in each time point of each group. Data were statistically analyzed with analysis of variance for factorial design and least significant difference test. Results: The body weights of rats in 2 groups before injury and at each time point post injury were close (P>0.05). At 6 h post injury, the weight of extensor digitorum longus of rats in scald group was (0.107±0.007) g, which was significantly heavier than (0.086±0.0607) g of sham injury group (P<0.01). On 3 d post injury, the weight of extensor digitorum longus of rats in scald group was (0.083±0.016) g, which was significantly lighter than (0.102±0.005) g of sham injury group (P<0.01). The weight of soleus of rats in 2 groups were close at each time point post injury (P>0.05). Compared with those of sham injury group, the mRNA expression of MAFbx in tibialis anterior muscle of rats in scald group was significantly up-regulated at 6 h post injury (P<0.01), and the mRNA expressions of MuRF1 in tibial anterior muscle of rats in scald group were significantly up-regulated at 6 h and on 1 d post injury (P<0.01). At 6 h and on 7 d post injury, compared with those of false injury group, the AMP/ATP ratios of the tibial anterior muscle of rats in scald group were significantly increased (P<0.05 or P<0.01), and energy charges of the tibial anterior muscle of rats in scald group were significantly decreased (P<0.01). At each time point post injury, the protein expressions of AMPK-α of the tibial anterior muscle of rats in 2 groups were close (P>0.05). The p-AMPK-α/AMPK-α ratios of the tibial anterior muscle of rats in scald group at 6 h and on 7 d post injury were significantly higher than those in sham injury group (P<0.05 or P<0.01). Conclusions: The decrease in energy charge and increase in AMP/ATP ratio of skeletal muscle of rats after severe scald activate AMPK. The activation of AMPK in the early stage of injury is consistent with the up-regulation of MAFbx and MuRF1 expressions and down-regulation of skeletal muscle weight. The above-mentioned changes may be one of the molecular mechanisms of skeletal muscle atrophy in rats with severe scald.

Impairment of PGC-1 Alpha Up-Regulation Enhances Nitrosative Stress in the Liver during Acute Pancreatitis in Obese Mice.

Acute pancreatitis is an inflammatory process of the pancreatic tissue that often leads to distant organ dysfunction. Although liver injury is uncommon in acute pancreatitis, obesity is a risk factor for the development of hepatic complications. The aim of this work was to evaluate the role of PGC-1α in inflammatory response regulation in the liver and its contribution to the detrimental effect of obesity on the liver during acute pancreatitis. For this purpose, we induced acute pancreatitis by cerulein in not only wild-type (WT) and PGC-1α knockout (KO) mice, but also in lean and obese mice. PGC-1α levels were up-regulated in the mice livers with pancreatitis. The increased PGC-1α levels were bound to p65 to restrain its transcriptional activity toward Nos2. Lack of PGC-1α favored the assembly of the p65/phospho-STAT3 complex, which promoted Nos2 expression during acute pancreatitis. The increased transcript Nos2 levels and the pro-oxidant liver status caused by the down-regulated expression of the PGC-1α-dependent antioxidant genes enhanced nitrosative stress and decreased energy charge in the livers of the PGC-1α KO mice with pancreatitis. It is noteworthy that the PGC-1α levels lowered in the obese mice livers, which increased the Nos2 mRNA expression and protein nitration levels and decreased energy charge during pancreatitis. In conclusion, obesity impairs PGC-1α up-regulation in the liver to cause nitrosative stress during acute pancreatitis.

Metabolic analysis of salicylic acid-induced chilling tolerance of banana using NMR.

Banana is highly susceptible to low temperature and salicylic acid (SA) can effectively improve the chilling tolerance. The metabolic changes of SA induced chilling responses of banana were studied. Bananas normally ripened under 15°C and dramatic metabolic difference compared with other groups was recorded. Accumulation of glucose (>1.5 folds) and consumption of unsaturated fatty acids (11.0-16.5%) were observed. The glycolysis was induced to compensate the decreased energy charge. Low temperature (6°C) caused chilling damage and metabolites including glutamine, serine, and glucose were related to chilled bananas. Various physiological changes such as sugar metabolism and consumption of reducing substances occurred to adapt the cold stress. SA released the cold injury and the disaccharides were increased by 18.1-21.4%. Further analysis revealed the synthesis of unsaturated fatty acids, amino acids such as proline, and enhanced energy charge. Thus, SA increased the chilling tolerance via a number of different metabolic mechanisms.

Derangements of amino acids in cachectic skeletal muscle are caused by mitochondrial dysfunction.

BackgroundCachexia is the direct cause of at least 20% of cancer‐associated deaths. Muscle wasting in skeletal muscle results in weakness, immobility, and death secondary to impaired respiratory muscle function. Muscle proteins are massively degraded in cachexia; nevertheless, the molecular mechanisms related to this process are poorly understood. Previous studies have reported conflicting results regarding the amino acid abundances in cachectic skeletal muscle tissues. There is a clear need to identify the molecular processes of muscle metabolism in the context of cachexia, especially how different types of molecules are involved in the muscle wasting process.MethodsNew in situ ‐omics techniques were used to produce a more comprehensive picture of amino acid metabolism in cachectic muscles by determining the quantities of amino acids, proteins, and cellular metabolites. Using matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging, we determined the in situ concentrations of amino acids and proteins, as well as energy and other cellular metabolites, in skeletal muscle tissues from genetic mouse cancer models (n = 21) and from patients with cancer (n = 6). Combined results from three individual MALDI mass spectrometry imaging methods were obtained and interpreted. Immunohistochemistry staining for mitochondrial proteins and myosin heavy chain expression, digital image analysis, and transmission electron microscopy complemented the MALDI mass spectrometry imaging results.ResultsMetabolic derangements in cachectic mouse muscle tissues were detected, with significantly increased quantities of lysine, arginine, proline, and tyrosine (P = 0.0037, P = 0.0048, P = 0.0430, and P = 0.0357, respectively) and significantly reduced quantities of glutamate and aspartate (P = 0.0008 and P = 0.0124). Human skeletal muscle tissues revealed similar tendencies. A majority of altered amino acids were released by the breakdown of proteins involved in oxidative phosphorylation. Decreased energy charge was observed in cachectic muscle tissues (P = 0.0101), which was related to the breakdown of specific proteins. Additionally, expression of the cationic amino acid transporter CAT1 was significantly decreased in the mitochondria of cachectic mouse muscles (P = 0.0133); this decrease may play an important role in the alterations of cationic amino acid metabolism and decreased quantity of glutamate observed in cachexia.ConclusionsOur results suggest that mitochondrial dysfunction has a substantial influence on amino acid metabolism in cachectic skeletal muscles, which appears to be triggered by diminished CAT1 expression, as well as the degradation of mitochondrial proteins. These findings provide new insights into the pathobiochemistry of muscle wasting.

Energy status regulates disease development and respiratory metabolism of Lasiodiplodia theobromae (Pat.) Griff. & Maubl.-infected longan fruit

Lasiodiplodia theobromae (Pat.) Griff. & Maubl. is a major pathogen causing decay of harvested longan fruit. The roles of energy status regulated by 2,4-dinitrophenol (DNP) and adenosine triphosphate (ATP) in disease development regarding respiratory metabolism of L. theobromae-inoculated “Fuyan” longan fruit were studied. Compared with L. theobromae-inoculated longans, DNP treatment could promote the index of fruit disease, accelerate the decrease in energy charge, increase respiration rate and the activities of respiratory terminal oxidases like CCO, AAO and PPO, elevate contents of NAD and NADH, but decrease NAD kinase activity, as well as contents of NADP and NADPH; however, exogenous ATP supply acted contrarily. Above results suggested the different energy status caused by DNP and ATP treatments accelerated or delayed the disease development of L. theobromae-inoculated longans via regulating Embden-Meyerhof pathway (EMP) and tricarboxylic acid (TCA) cycle, pentose phosphate pathway (PPP) and activities of respiratory terminal oxidases.

Hydrogen Peroxide Induced Changes in Energy Status and Respiration Metabolism of Harvested Longan Fruit in Relation to Pericarp Browning.

Energy status and respiration metabolism of "Fuyan" longan fruit treated by hydrogen peroxide (H2O2) and their relationship to pericarp browning were studied. The results displayed that H2O2 significantly increased the respiration rate, increased activities of respiratory terminal oxidases like cytochrome C oxidase (CCO) and ascorbic acid oxidase (AAO), decreased NAD kinase activity, maintained lower contents of NADP and NADPH as well as higher amounts of NAD and NADH, and accelerated the decrease of energy charge. These results gave convincing evidence that the treatment of H2O2 for accelerating longan pericarp browning was due to an increase of energy deficiency, an increase of respiratory metabolic pathways of Embden-Meyerhof pathway (EMP) and tricarboxylic acid (TCA) cycle, a decrease of pentose phosphate pathway (PPP) of respiratory pathway, and an increase of activities of respiratory terminal oxidases like CCO and AAO.

Adenosine A₁ receptors control the metabolic recovery after hypoxia in rat hippocampal slices.

Adenosine is a neuromodulator that protects neurons from hypoxia. This effect is attributed to the ability of adenosine A1 receptors (A1 R) to inhibit excitatory synaptic transmission. However, A1 R activation also protects non-brain tissues from hypoxic insults by controlling metabolism. Thus, we now tested the hypothesis that A1 R-mediated neuroprotection after a hypoxic insult in superfused hippocampal slices also involves the control of neuronal and astrocytic metabolism. A 90-min hypoxia insult increased lactate, alanine, and pyruvate levels and decreased energy charge (EC), phosphocreatine/creatine ratio, and glutamine content. These metabolic modifications were fully recovered after reoxygenation for 3 h. The presence of the A1 R-selective antagonist 1,3-dipropyl-8-cyclopentylxanthine stimulated glycolysis, prevented the hypoxia-induced decrease of EC, and increased the levels of GABA. A1 R blockade further blunted the recovery of metabolism on reoxygenation after hypoxia, as typified by a sustained decreased EC and an increased mitochondrial metabolism, as confirmed by a greater [U-(13) C]glucose oxidation through the tricarboxylic acid cycle. These results demonstrate that A1 R blockade prevents the recovery of hypoxia-induced metabolic alterations during reoxygenation, which indicates that the ability of A1 R to control primary metabolism in the brain tissue may be a hitherto unrecognized mechanism of A1 R-mediated neuroprotection. This study demonstrates that tonic activation of adenosine A1 receptors (A1 R) plays an important role in the reoxygenation recovery of the metabolic alterations caused by transient hypoxia in rat hippocampal slices. This ability of A1 R to inhibit neuronal metabolism may be a key mechanism by which adenosine affords neuroprotection upon acute hypoxia, thus preventing the long-term impairment of neuronal circuits.

Extracellular hyperosmotic stress stimulates glucose uptake in incubated fast-twitch rat skeletal muscle

The influence of hyperosmotic stress on glucose uptake, handling, and signaling processes remains unclear in mammalian skeletal muscle. Thus, the purpose of this study was to investigate alterations in glucose uptake and handling during extracellular hyperosmotic stress in isolated fast-twitch mammalian skeletal muscle. Using an established in vitro isolated whole-muscle model, extensor digitorum longus (EDL) muscles were dissected from male rats (4-6 weeks of age) and incubated (30-60 min) in an organ bath, containing Sigma Medium-199 with 8 mmol·L(-1) D-glucose, and mannitol was added to the targeted osmolalities (ISO, iso-osmotic, 290 mmol·kg(-1); HYPER, hyperosmotic, 400 mmol·kg(-1)). Results demonstrate that relative water content decreased in HYPER. HYPER resulted in significant alterations in muscle metabolite concentrations (lower glycogen, elevated lactate, and glucose-6-phosphate), suggesting a decrease in energy charge. Glucose uptake was also found to be higher in HYPER, and AS160 (implicated in insulin- and contraction-mediated glucose uptake) was found to be significantly more phosphorylated in HYPER than in ISO after 30 min. In conclusion, glucose uptake and handling is altered with hyperosmotic extracellular stress in the fast-twitch EDL. The increases in glucose uptake might be facilitated through alterations in AS160 signaling after 30 to 60 min of osmotic stress.

Changes in glucose uptake rate and in the energy status of PC-12 cells acutely exposed to hexavalent chromium, an established human carcinogen

In the 1920s, Otto Warburg reported a striking metabolic shift in solid tumors: contrary to their normal counter parts, which exhibited a nearly pure respiratory metabolism, where cancer cells relied strongly on lactic fermentation for energy production, even in the presence of ample oxygen. This metabolic shift, later named the Warburg effect, is now viewed as a nearly universal cancer phenotype. To investigate whether it is operating in hexavalent chromium (Cr(VI))-induced carcinogenesis, PC-12 cells were exposed to low Cr(VI) concentrations and effects determined on the rates of glucose uptake, lactate production and oxygen consumption, critical indicators of the type of energy metabolism adopted by the cells. Further, the influence on the cells’ energy charge, an important parameter in the evaluation of the cellular physiological state was assessed. In the presence of ample oxygen, concentration-dependent, statistically significant decreases in the energy charge were detected, which were accompanied by an increased glucose uptake rate. This enhanced uptake may constitute the first step in a compensatory mechanism aimed at counteracting the decrease in energy charge. Although these changes may be too small to exert an impact in the cellular functions, they may provide insight into the initial steps of Cr(VI)-induced carcinogenesis.

Enhanced glucose uptake via GLUT4 fuels recovery from calcium overload after ischaemia–reperfusion injury in sevoflurane- but not propofol-treated hearts

So far, no study has explored the effects of sevoflurane, propofol, and Intralipid on metabolic flux rates of fatty acid oxidation (FOX) and glucose oxidation (GOX) in hearts exposed to ischaemia-reperfusion. Isolated paced working rat hearts were exposed to 20 min of ischaemia and 30 min of reperfusion. Peri-ischaemic sevoflurane (2 vol%) and propofol (100 µM) in the formulation of 1% Diprivan(®) were assessed for their effects on oxidative energy metabolism and intracellular diastolic and systolic Ca(2+) concentrations. Substrate flux was measured using [(3)H]palmitate and [(14)C]glucose and [Ca(2+)] using indo-1AM. Western blotting was used to determine the expression of the sarcolemmal glucose transporter GLUT4 in lipid rafts. Biochemical analyses of nucleotides, ceramides, and 32 acylcarnitines were also performed. Sevoflurane, but not propofol, improved the recovery of left ventricular work (P=0.008) and myocardial efficiency (P=0.008) compared with untreated ischaemic hearts. This functional improvement was accompanied by reduced increases in post-ischaemic diastolic and systolic intracellular Ca(2+) concentrations (P=0.008). Sevoflurane, but not propofol, increased GOX (P=0.009) and decreased FOX (P=0.019) in hearts exposed to ischaemia-reperfusion. GLUT4 expression was markedly increased in lipid rafts of sevoflurane-treated hearts (P=0.016). Increased GOX closely correlated with reduced Ca(2+) overload. Intralipid alone decreased energy charge and increased long-chain and hydroxyacylcarnitine tissue levels, whereas sevoflurane decreased toxic ceramide formation. Enhanced glucose uptake via GLUT4 fuels recovery from Ca(2+) overload after ischaemia-reperfusion in sevoflurane- but not propofol-treated hearts. The use of a high propofol concentration (100 µM) did not result in similar protection.

Effect of nadolol, a beta-adrenoceptor blocking agent, on myocardial metabolism in the dog ischaemic heart.

The effect of nadolol at a dose of 1 mg kg-1, i.v. on the ischaemic myocardial metabolism has been examined in the dog. Ischaemia was induced by ligating the left anterior descending coronary artery for 3 min, and nadolol was injected 5 min before ligation. Ischaemia caused myocardial metabolic changes; it decreased energy charge potential and inhibited glycolytic flux through phosphofructokinase reaction. Pretreatment with nadolol lessened the decrease in energy charge potential and the inhibition of glycolytic flux being caused by ischaemia. Nadolol may have a beneficial effect on the ischaemic myocardium.

Dynamics of energy charge and adenine nucleotides during uncoupling of catabolism and anabolism in Penicillium ochrochloron

Filamentous fungi are able to spill energy when exposed to energy excess by uncoupling catabolism from anabolism, e.g. via overflow metabolism. In current study we tested the hypothesis that overflow metabolism is regulated via the energetic status of the hyphae (i.e. energy charge, ATP concentration). This hypothesis was studied in Penicillium ochrochloron during the steady state of glucose- or ammonium-limited chemostat cultures as well as during three transient states ((i) glucose pulse to a glucose-limited chemostat, (ii) shift from glucose-limited to ammonium-limited conditions in a chemostat, and (iii) ammonium exhaustion in batch culture). Organic acids were excreted under all conditions, even during exponential growth in batch culture as well as under glucose-limited conditions in a chemostat. Partial uncoupling of catabolism and anabolism via overflow metabolism was thus constitutively present. Under all tested conditions, overflow metabolism was independent of the energy charge or the ATP concentration of the hyphae. There was a reciprocal correlation between glucose uptake rate and intracellular adenine nucleotide content. During all transients states a rapid decrease in energy charge and the concentrations of nucleotides was observed shortly after a change in glycolytic flux (“ATP paradoxon”). A possible connection between the change in adenine nucleotide concentrations and the purine salvage pathway is discussed.

A Ca(2+)-calmodulin-eEF2K-eEF2 signalling cascade, but not AMPK, contributes to the suppression of skeletal muscle protein synthesis during contractions.

Skeletal muscle protein synthesis rate decreases during contractions but the underlying regulatory mechanisms are poorly understood. It was hypothesized that there would be a coordinated regulation of eukaryotic elongation factor 2 (eEF2) and eukaryotic initiation factor 4E-binding protein 1 (4EBP1) phosphorylation by signalling cascades downstream of rises in intracellular [Ca(2+)] and decreased energy charge via AMP-activated protein kinase (AMPK) in contracting skeletal muscle. When fast-twitch skeletal muscles were contracted ex vivo using different protocols, the suppression of protein synthesis correlated more closely with changes in eEF2 than 4EBP1 phosphorylation. Using a combination of Ca(2+) release agents and ATPase inhibitors it was shown that the 60-70% suppression of fast-twitch skeletal muscle protein synthesis during contraction was equally distributed between Ca(2+) and energy turnover-related mechanisms. Furthermore, eEF2 kinase (eEF2K) inhibition completely blunted increases in eEF2 phosphorylation and partially blunted (i.e. 30-40%) the suppression of protein synthesis during contractions. The 3- to 5-fold increase in skeletal muscle eEF2 phosphorylation during contractions in situ was rapid and sustained and restricted to working muscle. The increase in eEF2 phosphorylation and eEF2K activation were downstream of Ca(2+)-calmodulin (CaM) but not other putative activating factors such as a fall in intracellular pH or phosphorylation by protein kinases. Furthermore, blunted protein synthesis and 4EBP1 dephosphorylation were unrelated to AMPK activity during contractions, which was exemplified by normal blunting of protein synthesis during contractions in muscles overexpressing kinase-dead AMPK. In summary, in fast-twitch skeletal muscle, the inhibition of eEF2 activity by phosphorylation downstream of Ca(2+)-CaM-eEF2K signalling partially contributes to the suppression of protein synthesis during exercise/contractions.

Anaerobic homolactate fermentation withSaccharomyces cerevisiaeresults in depletion of ATP and impaired metabolic activity

Conversion of glucose to lactic acid is stoichiometrically equivalent to ethanol formation with respect to ATP formation from substrate-level phosphorylation, redox equivalents and product yield. However, anaerobic growth cannot be sustained in homolactate fermenting Saccharomyces cerevisiae. ATP-dependent export of the lactate anion and/or proton, resulting in net zero ATP formation, is suspected as the underlying cause. In an effort to understand the mechanisms behind the decreased lactic acid production rate in anaerobic homolactate cultures of S. cerevisiae, aerobic carbon-limited chemostats were performed and subjected to anaerobic perturbations in the presence of high glucose concentrations. Intracellular measurements of adenosine phosphates confirmed ATP depletion and decreased energy charge immediately upon anaerobicity. Unexpectedly, readily available sources of carbon and energy, trehalose and glycogen, were not activated in homolactate strains as they were in reference strains that produce ethanol. Finally, the anticipated increase in maximal velocity (V(max)) of glycolytic enzymes was not observed in homolactate fermentation suggesting the absence of protein synthesis that may be attributed to decreased energy availability. Essentially, anaerobic homolactate fermentation results in energy depletion, which, in turn, hinders protein synthesis, central carbon metabolism and subsequent energy generation.

Hypoxia Tolerance in Reptiles, Amphibians, and Fishes: Life with Variable Oxygen Availability

The ability of fishes, amphibians, and reptiles to survive extremes of oxygen availability derives from a core triad of adaptations: profound metabolic suppression, tolerance of ionic and pH disturbances, and mechanisms for avoiding free-radical injury during reoxygenation. For long-term anoxic survival, enhanced storage of glycogen in critical tissues is also necessary. The diversity of body morphologies and habitats and the utilization of dormancy have resulted in a broad array of adaptations to hypoxia in lower vertebrates. For example, the most anoxia-tolerant vertebrates, painted turtles and crucian carp, meet the challenge of variable oxygen in fundamentally different ways: Turtles undergo near-suspended animation, whereas carp remain active and responsive in the absence of oxygen. Although the mechanisms of survival in both of these cases include large stores of glycogen and drastically decreased metabolism, other mechanisms, such as regulation of ion channels in excitable membranes, are apparently divergent. Common themes in the regulatory adjustments to hypoxia involve control of metabolism and ion channel conductance by protein phosphorylation. Tolerance of decreased energy charge and accumulating anaerobic end products as well as enhanced antioxidant defenses and regenerative capacities are also key to hypoxia survival in lower vertebrates.

Effects of anti-ethylene treatments on browning and energy metabolism of harvested litchi fruit

Litchi fruit were treated with 10 mL/L ethylene (C2H4), 0.1% cobalt chloride (CoCl2) and 1 mL/L 1-methylcyclopropene, respectively, packed individually in closed but vented containers, and then stored at ambient temperature (28–33°C). The effects of these treatments on the browning, energy metabolism and disease incidence of the fruit were investigated. Treatment with C2H4 enhanced the activities of polyphenol oxidase and phenylalanine ammonia-lyase. Ethylene also increased the accumulation of ADP and AMP, but decreased energy charge in fruit peel. Cobalt chloride treatment had an inhibitory effect on increases of peroxidase activity, ATP : ADP ratio, energy charge and ATP, ADP and AMP. Browning index was reduced by 8.4 and 10.4% and disease index was reduced by 10.7 and 12.7% in CoCl2 and 1-methylcyclopropene-treated fruit, respectively, suggesting a relationship between energy metabolism, browning and disease index.