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At least 793 records · Page 44Linked to original sources
PubMed1992

ConA induced changes in energy metabolism of rat thymocytes.

The influence of ConA on the energy metabolism of quiescent rat thymocytes was investigated by measuring the effects of inhibitors of protein synthesis, proteolysis, RNA/DNA synthesis, Na+K(+)-ATPase, Ca(2+)-ATPase and mitochondrial ATP synthesis on respiration. Only about 50% of the coupled oxygen consumption of quiescent thymocytes could be assigned to specific processes using two different media. Under these conditions the oxygen is mainly used to drive mitochondrial proton leak and to provide ATP for protein synthesis and cation transport, whereas oxygen consumption to provide ATP for RNA/DNA synthesis and ATP-dependent proteolysis was not measurable. The mitogen ConA produced a persistent increase in oxygen consumption by about 30% within seconds. After stimulation more than 80% of respiration could be assigned to specific processes. The major oxygen consuming processes of ConA-stimulated thymocytes are mitochondrial proton leak, protein synthesis and Na+K(+)-ATPase with about 20% each of total oxygen consumption, while Ca(2+)-ATPase and RNA/DNA synthesis contribute about 10% each. Quiescent thymocytes resemble resting hepatocytes in that most of the oxygen consumption remains unexplained. In contrast, the pattern of energy metabolism in stimulated thymocytes is similar to that described for Ehrlich Ascites tumour cells and splenocytes, which may also be in an activated state. Most of the oxygen consumption is accounted for, so the unexplained process(es) in unstimulated cells shut(s) off on stimulation.

Animals↗
PubMed1992

ConA induced changes in energy metabolism of rat thymocytes.

The influence of ConA on the energy metabolism of quiescent rat thymocytes was investigated by measuring the effects of inhibitors of protein synthesis, proteolysis, RNA/DNA synthesis, Na+K(+)-ATPase, Ca(2+)-ATPase and mitochondrial ATP synthesis on respiration. Only about 50% of the coupled oxygen consumption of quiescent thymocytes could be assigned to specific processes using two different media. Under these conditions the oxygen is mainly used to drive mitochondrial proton leak and to provide ATP for protein synthesis and cation transport, whereas oxygen consumption to provide ATP for RNA/DNA synthesis and ATP-dependent proteolysis was not measurable. The mitogen ConA produced a persistent increase in oxygen consumption by about 30% within seconds. After stimulation more than 80% of respiration could be assigned to specific processes. The major oxygen consuming processes of ConA-stimulated thymocytes are mitochondrial proton leak, protein synthesis and Na+K(+)-ATPase with about 20% each of total oxygen consumption, while Ca(2+)-ATPase and RNA/DNA synthesis contribute about 10% each. Quiescent thymocytes resemble resting hepatocytes in that most of the oxygen consumption remains unexplained. In contrast, the pattern of energy metabolism in stimulated thymocytes is similar to that described for Ehrlich Ascites tumour cells and splenocytes, which may also be in an activated state. Most of the oxygen consumption is accounted for, so the unexplained process(es) in unstimulated cells shut(s) off on stimulation.

Adenosine Triphosphate↗
PubMed2003

Dehydroabietic acid, a major component of wood industry effluents, interferes with cellular energetics in rainbow trout hepatocytes.

We studied the effects of dehydroabietic acid (DHAA), a major toxic resin acid in wood industry effluents, on cellular energetics in rainbow trout (Oncorhynchus mykiss) hepatocytes. In addition, the role of DHAA-induced change in intracellular Ca(2+) in the energetic responses of the cells was evaluated. At sublytic concentrations, DHAA caused a reduction in cellular ATP content and a concomitant enhancement of glycolytic activity of the cells in a dose-dependent manner. No further decrease of cellular ATP content occurred after 60 min of DHAA-treatment indicating establishment of new energetic steady state in cells. DHAA also caused a rapid dose-dependent increase in oxygen consumption and in cellular heat production of the hepatocytes. The effect of DHAA on ATP content and glycolytic activity was independent from Ca(2+), whereas, changes in oxygen consumption and heat production were Ca(2+) -dependent. These results show that DHAA induces energetic imbalance in rainbow trout hepatocytes, which is apparently not due to direct interference of DHAA with ATP production nor does it seem to be caused by an indirect effect of elevated intracellular Ca(2+) concentration on mitochondrial energetics. Therefore, the ATP depletion is likely due to increased cellular ATP consumption caused by amphiphilic action of DHAA on the cell membrane.

Abietanes↗
PubMed2006

Energy metabolism of the inner cell mass and trophectoderm of the mouse blastocyst.

Mammalian pre-implantation development culminates in the formation of the blastocyst consisting of two distinct cell lineages, approximately a third of the cells comprise the pluripotent inner cell mass (ICM) and the remainder the differentiated trophectoderm (TE). However, the contribution made by these two cell types to the overall energy metabolism of the intact blastocyst has received relatively little attention. In this study, the metabolism of the intact mouse blastocyst and isolated ICMs were determined in terms of total ATP formation (calculated from oxygen consumption and lactate formation), mitochondrial distribution and amino acid turnover to provide an indication of protein synthesis. The TE consumed significantly more oxygen, produced more ATP and contained a greater number of mitochondria than the ICM. Amino acid turnover was significantly greater (p<0.001) in the TE compared with the ICM. Specifically, there was a significant difference in the utilization of aspartate (p=0.020), glutamate (p=0.024), methionine (p=0.037), and serine (p=0.041) between the cells of the ICM and TE. These data suggest that the TE produces approximately 80% of the ATP generated and is responsible for 90% of amino acid turnover compared with the ICM. The major fate of the energy produced by the TE is likely to be the Na(+), K(+)ATPase (sodium pump enzyme) located on the TE basolateral membrane. In conclusion, the pluripotent cells of the ICM display a relatively quiescent metabolism in comparison with that of the TE.

Adenosine Triphosphate↗
PubMed1995

Adenylate kinase-catalyzed phosphoryl transfer couples ATP utilization with its generation by glycolysis in intact muscle.

We previously suggested that an importance of adenylate kinase (AdK) in skeletal muscle is to function as a high energy phosphoryl transfer system regulating ATP generation in correspondence with its consumption by specific cellular processes. The present experiments are intended to define the ATP-generating system coupled to and regulated by AdK-catalyzed phosphotransfer in skeletal muscle and also to examine the relationship between AdK- and creatine kinase (CK)-catalyzed phosphotransfer. Rates of phosphoryl transfer catalyzed by AdK were assessed in intact, isolated rat diaphragm by determining rates of AMP phosphorylation with endogenously generated [gamma-18O]ATP under conditions of altered anaerobic and aerobic ATP production. AdK-catalyzed phosphoryl transfer rates accelerated incrementally up to 12-fold in direct proportion to stimulated contractile frequency in parallel with equivalent increases in rates of ATP generation by lactate producing glycolysis. Stoichiometric equivalent increases of AdK-catalyzed phosphotransfer and anaerobic ATP production also occurred up to more than 20-fold when oxidative phosphorylation was impaired by either O2 deprivation or treatment with KCN or p-(trifluoromethoxy)-phenylhydrazone. These enhanced rates of AMP phosphorylation were balanced by virtually identically increased rates of AdK-catalyzed generation of AMP. This AMP was traced to arise from AdK-catalyzed phosphotransfer involving ADP generated by a muscle ATPase. Increased AdK-catalyzed phosphotransfer paired with the apparent compensatory increase in ATP generation by anaerobic glycolysis in oxygen-deprived muscle occurred coincident with diminished rates of CK-catalyzed phosphoryl transfer indicative of a pairing between oxidatively produced ATP and CK-catalyzed phosphotransfer. A metabolic model consistent with these results and conforming to the Mitchell general principle of vectorial ligand conduction is suggested.

Adenosine Diphosphate↗
PubMed1993

[Anaerobic capacity--theoretical basis and methods for practical testing].

The ATP turnover rate is raised during highly intensive exercise. Part of the ATP used is regenerated anaerobically independently of oxygen consumption. Lactate production accounts for 75% of the anaerobic ATP production, while breakdown of phosphocreatine accounts for the remaining 25%. Anaerobic processes can provide energy for about one minute's exercise during exhausting exercise lasting several minutes. An athlete may improve his anaerobic capacity by 10% during two months of proper training, and the measured improvement is of significance for athletes. The accumulated oxygen deficit has been introduced to quantify the anaerobic release of energy during exercise. The method is discussed briefly.

Adenosine Triphosphate↗
PubMed1992

Modeling the effects of hypoxia on ATP turnover in exercising muscle.

Most models of metabolic control concentrate on the regulation of ATP production and largely ignore the regulation of ATP demand. We describe a model, based on the results of Hogan et al. (J. Appl. Physiol. 73: 728-736, 1992), that incorporates the effects of ATP demand. The model is developed from the premise that a unique set of intracellular conditions can be measured at each level of ATP turnover and that this relationship is best described by energetic state. Current concepts suggest that cells are capable of maintaining oxygen consumption in the face of declines in the concentration of oxygen through compensatory changes in cellular metabolites. We show that these compensatory changes can cause significant declines in ATP demand and result in a decline in oxygen consumption and ATP turnover. Furthermore we find that hypoxia does not directly affect the rate of anaerobic ATP synthesis and associated lactate production. Rather, lactate production appears to be related to energetic state, whatever the PO2. The model is used to describe the interaction between ATP demand and ATP supply in determining final ATP turnover.

Adenosine Triphosphate↗
PubMed1987

Relationship of myocardial metabolism and coronary flow: dependence on extracellular calcium.

The hypothesis that extracellular [Ca2+] ([Ca2+]e) influences the transmission of vasoregulatory information from the heart to coronary smooth muscle was examined. The isolated, retrogradely perfused rat heart was used to evaluate vascular reactivity to transient infusion of either 0.88 mM Amytal (amobarbital), hypoxia (95% N2-5% CO2), or 12 microM adenosine in the presence and absence of 2.5 microM verapamil. Amytal alone enhanced coronary flow by 78% and lactate efflux by 10-fold, whereas it decreased O2 consumption by 40% and the ratio of the free cytosolic concentrations of ATP-to-ADP times the intracellular concentration of inorganic phosphate ([ATP]f/[ADP]f[Pi]) by 10-fold. These responses were attenuated by preperfusion with verapamil, i.e., flow and lactate efflux increased by 4% and fourfold, respectively, and O2 consumption and [ATP]f/[ADP]f/[Pi] decreased by 8% and threefold, respectively, as compared with values attained with verapamil at steady state. Washout of the calcium channel antagonist by perfusion for 55 min with a verapamil-free medium resulted in a return of metabolic variables to control levels. Subsequent infusion of Amytal induced metabolic changes that were similar to those obtained before exposure to the calcium antagonist, but flow rose only by 26%. Vascular responses to hypoxia were similarly modified, whereas those to adenosine were unaffected. Hearts perfused with media containing either low [Ca2+]e or 10 microM diltiazem and exposed to Amytal produced flow patterns analogous to those perfused with verapamil. These data, in part, distinguish changes in vascular resistance that occur in response to cardiac metabolism from those which result from agents with direct action on smooth muscle, in particular, adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed2004

Imaging of ATP membrane transport with dual micro-disk electrodes and scanning electrochemical microscopy.

Extracellular adenosine-5'-triphosphate (ATP) is involved in a variety of relevant regulatory mechanisms at a cellular level and has therefore been focus of extensive research. One of the major challenges associated with measuring this key regulatory analyte is the ability to detect and localize extracellular ATP with sufficient spatial and temporal resolution in physiological environments. In this study, scanning electrochemical microscopy (SECM) utilizing an amperometric micro-biosensor based on co-immobilization of the enzymes glucose oxidase and hexokinase is applied for imaging ATP transport through a porous polycarbonate membrane under physiologically relevant conditions. The enzymatic biosensor operates on competitive consumption of the substrate glucose between the immobilized enzymes glucose oxidase and hexokinase involving ATP as a co-substrate. Quantitative determination of the ATP concentration is based on a linear correlation between the glucose consumption and the ATP level. Integration of the amperometric ATP micro-biosensor into a dual micro-disk electrode configuration is achieved by immobilizing the enzymes at one of the micro-disk electrodes while the second disk serves as an unmodified amperometric probe for controlled positioning of the micro-biosensor in close proximity to the sample surface enabling quantification of the obtained current signal.

Adenosine Triphosphate↗
PubMed1999

Indirect measurement of mitochondrial proton leak and its application.

In mitochondria, ATP synthesis is coupled to oxygen consumption by the proton electrochemical gradient established across the mitochondrial inner membrane in a process termed oxidative phosphorylation. It has long been known from stoichiometric studies that ATP synthesis is not perfectly coupled to oxygen consumption. The major inefficiency in the system is leakage of protons across the mitochondrial inner membrane driven by the proton electrochemical gradient. The kinetics of the proton leak can be determined indirectly, by measuring the oxygen consumption of mitochondria under non-phosphorylating conditions (plus oligomycin) as a function of the proton electrochemical gradient. This experimental system provides a convenient means to investigate inner membrane permeability to protons and the effect of factors that may effect that permeability. In this paper we review some results from our laboratory of indirect measurement of mitochondrial proton leak and how it has been applied to investigate the effect of aging, obesity and thyroid status on proton leak. The results show that (i) proton leak in isolated liver mitochondria is not significantly different in a comparison of young and old rats, in contrast (ii) there is an apparent increase in proton leak in in situ mitochondria in hepatocytes from old rats when compared to those from young rats, (iii) proton leak in neuronal mitochondria in situ in synaptosomes is not significantly different in young and old rats, (iv) proton leak is greater in isolated liver mitochondria from ob/ob mice compared to lean controls, (v) acute leptin (OB protein) administration restores the increased leak rate in isolated liver mitochondria from ob/ob mice to that of lean controls, (vi) administration of thyroid hormone (T3) increases proton leak in rat muscle mitochondria, and (vii) proton leak in muscle mitochondria is insensitive to the presence of GDP. It is proposed that the experimental system described here for measuring proton leak, is an ideal functional assay for determining whether the novel uncoupling proteins increase inner membrane permeability to protons.

Aging↗
PubMed2004

Some processes of energy saving and expenditure occurring during ethanol perfusion in the isolated liver of fed rats; a Nuclear Magnetic Resonance study.

BACKGROUND: In the isolated liver of fed rats, a 10 mM ethanol perfusion rapidly induced a rapid 25% decrease in the total ATP content, the new steady state resulting from both synthesis and consumption. The in situ rate of mitochondrial ATP synthesis without activation of the respiration was increased by 27%, implying an increased energy demand. An attempt to identify the ethanol-induced ATP-consuming pathways was performed using 31P and 13C Nuclear Magnetic Resonance. RESULTS: Ethanol (i) transiently increased sn-glycerol-3-phosphate formation whereas glycogenolysis was continuously maintained; (ii) decreased the glycolytic ATP supply and (iii) diminished the intracellular pH in a dose-dependent manner in a slight extend. Although the cytosolic oxidation of ethanol largely generated H+ (and NADH), intracellular pHi was maintained by (i) the large and passive excretion of cellular acetic acid arising from ethanol oxidation (evidenced by exogenous acetate administration), without energetic cost or (ii) proton extrusion via the Na+-HCO3- symport (implying the indirect activation of the Na+-K+-ATPase pump and thus an energy use), demonstrated during the addition of their specific inhibitors SITS and ouabaïn, respectively. CONCLUSION: Various cellular mechanisms diminish the cytosolic concentration of H+ and NADH produced by ethanol oxidation, such as (i) the large but transient contribution of the dihydroxyacetone phosphate/sn-glycerol-3-phosphate shuttle between cytosol and mitochondria, mainly implicated in the redox state and (ii) the major participation of acetic acid in passive proton extrusion out of the cell. These processes are not ATP-consuming and the latter is a cellular way to save some energy. Their starting in conjunction with the increase in mitochondrial ATP synthesis in ethanol-perfused whole liver was however insufficient to alleviate either the inhibition of glycolytic ATP synthesis and/or the implication of Na+-HCO3- symport and Na+-K+-ATPase in the pHi homeostasis, energy-consuming carriers.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1987

Adenine nucleotides in erythrocytes from patients with peripheral vascular disease and the effects of oxpentifylline.

The relationship between erythrocyte nucleotide profiles and the presence of atherosclerotic peripheral occlusive vascular disease was investigated. In elderly male patients with severe vascular insufficiency the mean red cell content of NAD, GDP, GTP, AMP, ADP and ATP and the cellular adenylate energy charge were not significantly different from those observed in young healthy males. It has been claimed that drugs such as oxpentifylline improve peripheral tissue oxygenation in vascular disease by reversing the fall in red cell ATP content which has been reported to accompany vascular insufficiency resulting in a restoration of normal cell deformability and hence whole blood viscosity. We have carried out in vitro studies using erythrocytes from normal adults to assess the effect of oxpentifylline on erythrocyte ATP content and glycolytic rate. The drug failed to significantly affect the rates of glucose consumption and lactate production or the ATP content of the erythrocytes compared with controls. Furthermore the drug did not influence the rate of ATP utilisation by erythrocytes. We conclude that red cell ATP and total adenylate content is not different from normal in patients with peripheral vascular disease. If oxpentifylline alters red cell deformability it does so by some mechanism not related to the cellular ATP concentration, the cellular adenylate energy charge or the glycolytic rate.

Adenine Nucleotides↗
PubMed1986

Alcohol and nutrition: caloric value, bioenergetics, and relationship to liver damage.

Alcoholic beverages contribute an appreciable percentage (4-6%) to the total caloric intake in Western societies. The caloric value of ethanol as fuel may be dose-related. Most evidence suggests that at moderate intake levels of less than 45 g/day (3 drinks) ethanol is efficiently utilized as a fuel by the liver. At high intakes, ethanol calories may not be utilized for cellular synthesis of ATP and maintenance of weight. The exact mechanism for this inefficient utilization remains unknown but may be related, in part, to metabolism of ethanol by the microsomal ethanol-oxidizing system, a reaction that does not contribute to generation of reducing equivalents for ATP synthesis. Although ethanol is utilized for ATP synthesis after single-dose administration, chronic consumption leads to morphological changes in hepatic mitochondria and to decreased ATP synthesis. Reductions in the activities of the enzymes of the mitochondrial electron transport chain have been reported after alcohol feeding and may help to explain decreases in hepatic ATP synthesis. There is some evidence that ATP degradation by "Na-K ATPase" is increased after ethanol feeding and that hepatic O2 consumption is likewise enhanced. However, other studies have failed to demonstrate enhanced O2 consumption. Current evidence suggests that malnutrition alone is not sufficient to explain the pathogenesis of chronic liver disease in alcoholics. Although the daily amount of alcohol consumed and the duration of excessive consumption are clearly important factors in the development of alcoholic hepatitis and cirrhosis, other factors, particularly nutritional deficiencies, may modulate the risk of developing alcohol-related liver damage. The prevalence of malnutrition is exceedingly high in alcoholics with clinically severe liver disease. Nutritional deficiencies are better correlated with a clinical index of severity than with histologic severity of alcoholic hepatitis. Prognosis and outcome of patients with alcoholic liver disease may be affected by nutritional deficiencies, which thus provides a rationale for aggressive nutritional management of these patients.

Acetaldehyde↗
PubMed2006

Multiparametric sensor-chip based technology for monitoring metabolic activity: A proof-of-principle study with live tissue.

The recent development of an electronic test system based on silicon sensor-chips allows the continuous parallel recording of relative changes in extracellular acidification, oxygen consumption and electric impedance in living cells. The objective of this proof-of-principle study therefore, was to clarify whether this system can also be applied to live tissue slices thus providing a device for an ultimately envisioned chemosensitivity testing apparatus for individualized treatment schemes in cancer therapy. A prototype of the testing apparatus equipped with six individual measuring devices has been used to simultaneously analyze changes in extracellular acidification, oxygen consumption and electronic impedance in live liver tissue and compared to data obtained from a tumor cell line. In contrast to tumor cells, tissue slices showed low rates of extracellular acidification but high rates of oxygen consumption. Monitoring of electrical impedance values, reflecting cellular morphology, revealed that the compact cell structure of the tissue slices was able to function as electric insulator and actively change the impedance values of the system. Exposure of tumor cells to 1 microM cytochalasin B, a fungal metabolite known to interact with the cytoskeleton and influence glucose metabolism, resulted in the rapid decline of extracellular acidification, increased oxygen consumption rates and increased values in capacitance. In tissue slices upon addition of 1 microM cytochalasin B, a decline of both extracellular acidification and electrical impedance was observed within 1 h. Determination of ATP content in the tissue slices revealed that decreasing ATP content paralleled diminishing oxygen consumption. This new technique offers the possibility of generating metabolic profiles for cells and tissues by studying oxygen consumption, extracellular acidification and electrical impedance.

Acid-Base Equilibrium↗
PubMed1977

The synthesis of hippurate from benzoate and glycine by rat liver mitochondria. Submitochondrial localization and kinetics.

1. Rat liver mitochondria make hippurate at up to 4 nmol/min per mg of protein. The rate of synthesis supported by oxidation of glutamate with exogenous Pi present is identical with that supported by ATP plus oligomycin. Lower rates were obtained with other respiratory substrates, and when glutamate was used without Pi. 2. A matrix localization for hippurate synthesis is indicated by the latency of benzoyl-CoA synthetase and glycine N-acyltransferase to their extramitochondrial substrates, failure of exogenous benzoyl-CoA to inhibit incorporation of [14C]hippurate and inhibition of hippurate synthesis supported by ATP, but not glutamate, by carboxyatractyloside. 3. The relative activities of the individual enzymes and the mitochondrial content of benzoyl-CoA in the presence and absence of glycine suggest that hippurate synthesis is rate-limited by formation of benzoyl-CoA. 4. The increases in rates of ATP hydrolysis and of O2 consumption on the addition of benzoate and glycine were in good agreement with those required to support hippurate synthesis. The increase in respiration indicates that State-4 respiration [Chance & Williams (1957) Adv. Enzymol 17, 65-134] is not used, with these conditions, for ATP synthesis.

Adenosine Triphosphate↗
PubMed1988

Velocity of the creatine kinase reaction decreases in postischemic myocardium: a 31P-NMR magnetization transfer study of the isolated ferret heart.

Recovery of postischemic function may be limited by energy synthesis by mitochondria, energy transfer via the creatine kinase reaction, or energy utilization at myofibrils. To identify the limiting step, we defined the relations among oxygen consumption, creatine kinase reaction velocity and cardiac performance in myocardium reperfused following mild, moderate, and severe ischemia. Isolated isovolumic ferret hearts were perfused with Krebs-Henseleit buffer at 37 degrees C. After 30 minutes of control, hearts were made ischemic for 20, 40, or 60 minutes and reperfused for 40 minutes. During preischemia, cardiac performance (estimated as the rate-pressure product), was 14.8 x 10(3) mm Hg/min, oxygen consumption was 16.7 mumol/min/g dry weight, and creatine kinase reaction velocity measured by 31P-nuclear magnetic resonance saturation transfer was 12.7 mM/sec. For hearts reperfused after 20, 40, or 60 minutes of ischemia, rate-pressure product was 11.5, 6.5, and 1.1 x 10(3) mm Hg/min; oxygen consumption was 13.5, 14.2, and 6.9 mumol/min/g dry weight; and creatine kinase reaction velocity was 9.6, 5.0, and 2.0 mM/sec, respectively. Thus, with increasing severity of insult, creatine kinase reaction velocity decreased monotonically with performance (r = 0.99). Changes in creatine kinase reaction velocity were predicted from the creatine kinase rate equation (r = 0.99; predicted vs. measured velocity) and can therefore be explained by changes in substrate concentration. Oxygen consumption did not correlate with performance or creatine kinase velocity, consistent with abnormalities in mitochondrial energy production. In all cases, creatine kinase reaction velocity was an order of magnitude faster than the maximal rate of ATP synthesis estimated by oxygen consumption. We conclude that, in postischemic myocardium, creatine kinase reaction velocity decreases in proportion to performance, but high-energy phosphate transfer does not limit availability of high-energy phosphate for contraction.

Animals↗
PubMed1995

Use of top-down elasticity analysis to identify sites of thyroid hormone-induced thermogenesis.

Top-down elasticity analysis is a novel extension of top-down metabolic control analysis. It has provided researchers with a theoretical and practical platform upon which quantitative analyses of the sites of action of hormones and drugs can be based. This approach is easy to apply and involves dividing up the metabolic system in question into two or three blocks of enzyme reactions around an intermediate between the blocks of reactions. The kinetic response of each block to the intermediate is measured in the steady state in situ by determining the flux through the block at different measured intermediate concentrations. The intermediate can be manipulated by titrating the other blocks with suitable inhibitors or activators. Then, to determine which blocks of reactions are quantitatively the most important in terms of any change in the flux rate of the system, a quantitative comparison of the titration curves from the experimental preparations is made with those of the control preparations. In this minireview we will examine, as an example, the use of top-down elasticity analysis for the quantitative identification of the important sites of action of thyroid hormones on oxidative phosphorylation in hepatocytes. The experimental results show that approximately 50% of the change in resting oxygen consumption in hepatocytes from hypothyroid and hyperthyroid rats (compared with euthyroid controls) is attributable to changes in the rate of the mitochondrial proton leak; the remaining 50% is accounted for by changes in nonmitochondrial- and ATP turnover-dependent oxygen consumption in hypothyroid and hyperthyroid hepatocytes, respectively.

Adenosine Triphosphate↗
PubMed2002

Mitochondrial ATP synthase--a possible target protein in the regulation of energy metabolism in vitro and in vivo.

The increasing prevalence of obesity in the Western world has stimulated an intense search for mechanisms regulating food intake and energy balance. A number of appetite-regulating peptides have been identified, their receptors cloned and the intracellular events characterized. One possible energy-dissipating mechanism is the mitochondrial uncoupling of ATP-synthesis from respiratory chain oxidation through uncoupling proteins, whereby energy derived from food could be dissipated as heat, instead of stored as ATP. The exact role of the uncoupling proteins in energy balance is, however, uncertain. We show here that mitochondrial F1F0-ATP synthase itself is a target protein for an anorectic peptide, enterostatin, demonstrated both after affinity purification of rat brain membranes and through a direct physical interaction between enterostatin and purified F1-ATP synthase. In insulinoma cells (INS-1) enterostatin was found to target F1F0-ATP synthase, causing an inhibition of ATP production, an increased thermogenesis and increased oxygen consumption. The experiments suggest a role of mitochondrial F1F0-ATP synthase in the suppressed insulin secretion induced by enterostatin. It could be speculated that this targeting mechanism is involved in the decreased energy efficiency following enterostatin treatment in rat.

Animals↗