Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ATP consumption”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed1986

Kinetics of energy consumption in human platelets with blocked ATP regeneration.

Abrupt arrest of ATP resynthesis in blood platelets induces a rapid decline in metabolic ATP-ADP. This decline is biexponential with a 7-fold difference in the rate-constants of the two components. Stimulation with thrombin increases both rate-constants, and raises the relative contribution of the rapid component from 60 to 90% of total. The initial decline can be approximated by a single exponential term, yielding the rate-constant for initial ATP hydrolysis. Since this initial decline reflects energy consumption of undisturbed platelets, this approach offers a sensitive means to determine energy consumption and ATP turnover within short time intervals.

Adenosine Diphosphate↗
PubMed2003

Control analysis of mitochondrial metabolism in intact hepatocytes: effect of interleukin-1beta and interleukin-6.

Interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) are produced by hepatic nonparenchymal cells after systemic injury and have been reported to inhibit ATP synthesis in hepatocytes, which may contribute to hepatic dysfunction in inflammatory states. To elucidate the mechanisms of action of IL-1beta and IL-6 on hepatocellular ATP synthesis, we measured the oxygen uptake rate (OUR) and mitochondrial membrane potential (MMP) of stable hepatocyte cultures, and analyzed the dynamic MMP response following the addition of mitochondrial inhibitors (antimycin A and oligomycin) with a model of mitochondrial metabolism. IL-1beta reduced mitochondrial OUR coupled to ATP synthesis via inhibition of phosphorylation reactions which dissipate the MMP, including ATP synthesis and consumption. Furthermore, the ATP synthesis rate in cytokine-free and IL-1beta-treated hepatocytes was controlled primarily by phosphorylation reactions, which corresponds to a state where the ATP synthesis rate closely follows the cellular energy demand. Thus, IL-1beta-mediated effects on electron transport and substrate oxidation reactions are not likely to significantly impact on ATP synthesis. IL-6 did not reduce mitochondrial OUR coupled to ATP synthesis, but shifted the control for ATP synthesis towards processes which generate the MMP, indicating that IL-6 induces a metabolic state where cellular functions are limited by the mitochondrial energy supply.

Adenosine Triphosphate↗
PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗
PubMed2004

Investigation of intracellular magnesium mobilization pathways I PC12 cells B simultaneous Mg-Ca fluorescent imaging.

OBJECTIVE AND METHODS: PC12 cells were loaded with a novel Mg indicator KMG-104 and Ca indicator fura-2, and intracellular Mg was studied in the endoplasmic reticulums (ERs), mitochondria, and Mg-ATP. Under coexistence of the two indicators, fluorescent signals of Mg and Ca can be measured separately. Mg release from the ER was investigated by photolysis of caged compounds. RESULTS: Transient [Ca]i increase by uncaging of caged Ca or caged IP3 or bath-application of caffeine (10 mM) induced no [Mg]i increase. These results suggest that there is no mechanism for Mg release from the ER through ryanodine receptors or IP3 receptors. In order to investigate the possibility of Mg release from Mg-ATP by energy consumption, we depleted ATP by oligomycin, an inhibitor of mitochondrial ATP synthase. Treating with oligomycin (4 microM) for several minutes showed no change of [Mg]i and [Ca]i. CONCLUSIONS: This result shows that Mg-ATP is not a Mg store. Since, when cells were treated by an uncoupler FCCP (3 microM), [Mg]i and [Ca]i increased, we concluded that mitochondria participate in maintenance of intracellular Mg stores.

Calcium↗
PubMed1975

Impairment of mitochondrial function following reperfusion of acutely ischemic myocardium.

This study examines indices of respiratory function in mitochondria prepared from transiently ischemic myocardium that had been reperfused in order to evaluate the validity of performing early surgical revascularization procedures. Experiments were performed in pigs with temporary ligation (15-80 min) of an anterior descending coronary artery followed by a 2-hr reperfusion period. Mitochondria preparations were studied simultaneously from normal and reperfused mitochondria in malate and glutamate substrates using the polarographic method. Results revealed a marked decrease of oxygen consumption of mitochondria from reperfused myocardium with relative preservation of oxidative phosphorylation (near normal ADP/O ratio). These results are compatible with a block in electron transport, a theory which was further supported by the data obtained using dinitrophenol as an uncoupler. Additional studies suggested the block was located at site I in the electron transport chain since mitochondrial oxygen consumption, including ATP-linked oxygen consumption, was enhanced by the use of succinate in combination with glutamate. The abnormal mitochondrial function observed is probably due to ischemia persisting despite reperfusion.

Acute Disease↗
PubMed2001

Selective blockade of mitochondrial K(ATP) channels does not impair myocardial oxygen consumption.

Opening of mitochondrial ATP-sensitive potassium (K(ATP)) channels has been postulated to prevent inhibition of respiration resulting from matrix contraction during high rates of ATP synthesis. Glibenclamide, which blocks K(ATP) channels on the sarcolemma of vascular smooth muscle cells and myocardial myocytes as well as on the inner mitochondrial membrane, results in a decrease of myocardial oxygen consumption (MVO2) both at rest and during exercise. This study examined whether this represents a primary effect of blockade of mitochondrial K(ATP) channels or occurs secondary to coronary resistance vessel constriction with a decrease of coronary blood flow (CBF) and myocardial oxygen availability. MVO2 was measured at rest and during treadmill exercise in 10 dogs during control conditions, after selective mitochondrial K(ATP) channel blockade with 5-hydroxydecanoate (5-HD), and after nonselective K(ATP) channel blockade with glibenclamide. During control conditions, exercise resulted in progressive increases of CBF and MVO2. Glibenclamide (50 microg x kg(-1) x min(-1) ic) resulted in a 17 +/- 6% decrease of resting CBF with a downward shift of CBF during exercise and a decrease of coronary venous PO2, indicating increased myocardial oxygen extraction. In contrast with the effects of glibenclamide, 5-HD (0.7 mg x kg(-1) x min(-1) ic) had no effect on CBF, MVO2, or myocardial oxygen extraction. These findings suggest that glibenclamide decreased MVO2 by causing resistance vessel constriction with a decrease of CBF and oxygen available to the myocardium rather than to a primary reduction of mitochondrial respiration.

Animals↗
PubMed2000

Simultaneous detection of mitochondrial respiratory chain activity and reactive oxygen in digitonin-permeabilized cells using flow cytometry.

BACKGROUND: Increased mitochondrial generation of reactive oxygen intermediates (ROI) due to defective respiratory chain activity has been implicated in physiological processes such as apoptosis, in the pathogenesis of mitochondrial diseases, and as part of the normal aging process. Established methods addressing activity of the respiratory chain complexes have been limited to bulk assays for single parameters. This study describes a flow cytometry-based method and its validation for the detection of respiratory chain function in single cells permeabilized by digitonin. METHODS: Flow cytometry was used to measure mitochondrial membrane potential (DeltaPsi(m)) and reactive oxygen generation under differing conditions of respiration. This was brought about by the addition of substrates and inhibitors to digitonin-permeabilized cells. This method was validated by measurement of oxygen consumption and ATP production and by confocal microscopy. RESULTS: Activity of the respiratory chain complexes assessed by DeltaPsi(m) responded to substrates and inhibitors as predicted from assessment by oxygen consumption and ATP synthesis. In addition, the flow cytometry method allows the simultaneous assessment of mitochondrial ROI generation. This was confirmed by the localization of the ROI probe, carboxy-DCF, to the same site as the mitochondrial probe observed by confocal microscopy. CONCLUSIONS: This method allows the functional integrity of the respiratory chain complexes to be studied at the single-cell level, thus addressing the relationship between disordered function of respiratory chain complexes and mitochondrial ROI generation.

Adenosine Triphosphate↗
PubMed2001

Evolutionary optimization of metabolic pathways. Theoretical reconstruction of the stoichiometry of ATP and NADH producing systems.

The structural design of ATP and NADH producing systems, such as glycolysis and the citric acid cycle (TCA), is analysed using optimization principles. It is assumed that these pathways combined with oxidative phosphorylation have reached, during their evolution, a high efficiency with respect to ATP production rates. On the basis of kinetic and thermodynamic principles, conclusions are derived concerning the optimal stoichiometry of such pathways. Extending previous investigations, both the concentrations of adenine nucleotides as well as nicotinamide adenine dinucleotides are considered variable quantities. This implies the consideration of the interaction of an ATP and NADH producing system, an ATP consuming system, a system coupling NADH consumption with ATP production and a system consuming NADH decoupled from ATP production. It is examined in what respect real metabolic pathways can be considered optimal by studying a large number of alternative pathways. The kinetics of the individual reactions are described by linear or bilinear functions of reactant concentrations. In this manner, the steady-state ATP production rate can be calculated for any possible ATP and NADH producing pathway. It is shown that most of the possible pathways result in a very low ATP production rate and that the very efficient pathways share common structural properties. Optimization with respect to the ATP production rate is performed by an evolutionary algorithm. The following results of our analysis are in close correspondence to the real design of glycolysis and the TCA cycle. (1) In all efficient pathways the ATP consuming reactions are located near the beginning. (2) In all efficient pathways NADH producing reactions as well as ATP producing reactions are located near the end. (3) The number of NADH molecules produced by the consumption of one energy-rich molecule (glucose) amounts to four in all efficient pathways. A distance measure and a measure for the internal ordering of reactions are introduced to study differences and similarities in the stoichiometries of metabolic pathways.

Adenosine Triphosphate↗
PubMed2005

Comparison of para-aminophenol cytotoxicity in rat renal epithelial cells and hepatocytes.

Several chemicals, including para-aminophenol (PAP), produce kidney damage in the absence of hepatic damage. Selective nephrotoxicity may be related to the ability of the kidney to reabsorb filtered water, thereby raising the intraluminal concentration of toxicants and exposing tubular epithelial cells to higher concentrations than would be present in other tissues. The present experiments tested the hypothesis that hepatocytes and renal epithelial cells exposed to equivalent concentrations of PAP would be equally susceptible to toxicity. Hepatocytes and renal epithelial cells were prepared by collagenase digestion of tissues obtained from female Sprague-Dawley rats. Toxicity was monitored using trypan blue exclusion, oxygen consumption and ATP content. We measured the rate of PAP clearance and formation of PAP-glutathione conjugate by HPLC. We found that renal epithelial cells accumulated trypan blue and showed declines in oxygen consumption and ATP content at significantly lower concentrations of PAP and at earlier time points than hepatocytes. The half-life of PAP in hepatocyte incubations was significantly shorter (0.71+/-0.07 h) than in renal epithelial cell incubations (1.33+/-0.23 h), suggesting that renal epithelial cells were exposed to PAP for longer time periods than hepatocytes. Renal epithelial cells formed significantly less glutathione conjugates of PAP (PAP-SG) than did hepatocytes, consistent with less efficient detoxification of reactive PAP intermediates by renal epithelial cells. Finally, hepatocytes contained significant more reduced glutathione (NPSH) than did renal epithelial cells, possibly explaining the enhanced formation of PAP-SG by this cell population. In conclusion, our data indicates that renal epithelial cells are intrinsically more susceptible to PAP cytotoxicity than are hepatocytes. This enhanced cytotoxicity may be due to longer exposure to PAP and/or reduced detoxification of reactive intermediates due to lower concentrations of reduced NPSH in renal epithelial cells than in hepatocytes.

Aminophenols↗
PubMed1983

Effect of maternal carbohydrate intake on mitochondrial activity and on lipogenesis by the young and mature progeny.

The influence of maternal dietary sucrose on lipogenesis and on oxygen consumption and ATP production by isolated hepatic mitochondria was studied. During gestation and lactation, female BHE rats were fed either a 65% starch or a 65% sucrose diet. At weaning, male progeny were fed either the diet of their dam or the alternate diet. Rates of oxygen consumption and ATP production from isolated hepatic mitochondria, rates of 3H incorporation into fatty acids, and percent liver lipid were determined at 50 and 150 days of age. Correlation coefficients between mitochondrial function and hepatic lipogenic activity were calculated. Analysis of variance of these data indicated that state IV oxygen consumption was influenced by age and by an interaction of the maternal diet and the diet fed the progeny from weaning. The respiratory control ratio was influenced by the interaction of the maternal diet and the diet fed the progeny and by the interaction of the maternal diet and the age of the progeny when killed. ATP synthesis and recovery of ADP as ATP was influenced by an interaction of all three variables: maternal diet, growth diet and age. In progeny killed at 150 (but not 50) days of age, sucrose feeding increased the incorporation of tritium into fatty acids. Liver lipid levels were influenced by age and diet. Mitochondrial ATP synthesis was negatively correlated with hepatic lipid content, and mitochondrial ATP recovery from ADP was negatively correlated with 3H incorporation and percent liver lipid. These results suggest that alterations in hepatic mitochondrial ATP production may be associated with the increase in hepatic lipid synthesis and serum lipid levels frequently observed in sucrose-fed animals as they age.

Adenosine Triphosphate↗
PubMed1976

Energy-linked regulation of glucose and pyruvate oxidation in isolated perfused rat heart. Role of pyruvate dehydrogenase.

1. The regulation of glycolysis and pyruvate oxidation under varying conditions of ATP and oxygen consumption was studied in isolated perfused rat hearts. Potassium-induced arrest was employed to inhibit the ATP consumption of the heart. 2. Under the experimental conditions, the beating heart used solely glucose as the oxidisable substrate. The glycolytic flux through the aldolase step decreased in pace with the decreasing oxygen consumption during the potassium-induced arrest of the heart. The decrease in glucose oxidation was larger than the inhibition of the oxygen consumption, suggesting that the arrested heart switches to fatty acid oxidation. The time course and percentage changes of the inhibition of pyruvate oxidation and the decrease in the amount of the active form of pyruvate dehydrogenase suggest that the amount of active pyruvate dehydrogenase is the main regulator of pyruvate oxidation in the perfused heart. 3. To test the relative significance of the possible mechanisms regulating covalent interconversions of pyruvate dehydrogenase, the following parameters were measured in response to the potassium-induced cardiac arrest: concentrations of pyruvate, acetyl-CoA, CoA-SH, citrate, alpha-oxoglutarate, ATP, ADP, AMP, creatine, creatine phosphate and inorganic phosphate and the mitochondrial NADH/NAD+ ratio. In cardiac tissue the adenylate system is not a good indicator of the energy state of the mitochondrion, even when the concentrations of AMP and free cytosolic ADP are calculated from the adenylate kinase and creatine kinase equilibria. Only creatine phosphate and inorganic phosphate undergo significant changes, but evidence of the participation of the latter compounds in the regulation of the pyruvate dehydrogenase interconversions is lacking. The potassium-induced arrest of the heart resulted in a decrease in pyruvate, a slight increase in acetyl-CoA, a large increase in the concentration of citrate and an increase in the mitochondrial NADH/NAD+. The results can be interpreted as showing that in the heart, the pyruvate dehydrogenase interconversions are mainly regulated by the pyruvate concentration and the mitochondrial redox state. Concentrations of all the regulators tested shifted to directions which one would expect to result in a decrease in the amount of active pyruvate dehydrogenase, but the changes were quite small. Therefore, the energy-linked regulation of pyruvate dehydrogenase in intact tissue is possibly mediated by the equilibrium relations between the cellular redox state and the phosphorylation potential recently confirmed in cardiac tissue.

Animals↗
PubMed1983

Stimulus-secretion coupling of glucose-induced insulin release. LI. Divalent cations and ATPase activity in pancreatic islets.

Pancreatic islets can be viewed as a fuel-sensor organ. The amount of ATP used by the islet cells for the maintenance of adequate Ca2+ gradients across membranes is not known. An indirect approach to this issue consists in the measurement of Ca-ATPase activity. The kinetics of Ca-ATPase in islet homogenates yielded a Km for ATP close to 0.1 mM and two Km values for Ca2+ close to 0.13 and 4-6 microM, respectively. Within limits, the Ca-ATPase appeared as a distinct entity from Mg-ATPase. Several divalent cations, including Mg2+, inhibited the Ca-ATPase activity. Calmodulin also inhibited, significantly albeit modestly Ca-ATPase. The activity of the enzyme was increased at high pH or in the presence of bicarbonate. The reaction velocity at close-to-physiological concentrations of ATP, Ca2+ and H+ suggests that the consumption of ATP by the Ca-ATPase may account for a major fraction of the overall rate of ATP breakdown in intact islets.

Adenosine Triphosphatases↗
PubMed2005

Time course of differential mitochondrial energy metabolism adaptation to chronic hypoxia in right and left ventricles.

OBJECTIVE: The present study was designed to characterize mitochondrial adaptation to chronic hypoxia (CH) in the rat heart. Mitochondrial energy metabolism was differentially examined in both left and right ventricles since CH selectively triggers pulmonary hypertension and right ventricular hypertrophy. METHODS: Rats were exposed to a hypobaric environment for 2 or 3 weeks and compared with rats maintained in a normoxic environment. Oxidative capacity (oxygen consumption and ATP synthesis) was measured in saponin-skinned fibers with glutamate or palmitoyl carnitine as substrates. Enzymatic activities of mitochondrial respiratory chain complexes were measured on tissue homogenates. Morphometric analysis of mitochondria was performed on electron micrographs. Mitochondrial DNA was quantified using Southern blot analysis. RESULTS: Whereas oxidative capacity of both ventricles was decreased following 21 days of CH, oxygen consumption and ATP synthesis was maintained with the glutamate substrate in the right ventricle following 14 days of CH. As for the oxidative capacity, enzyme activities were decreased only in the left ventricle following 14 days of CH and in both ventricles following 21 days of CH. These functional alterations were associated with an increase in numerical density and a decrease in size of mitochondria without a change in volume density in both ventricles. Finally, 21 days of CH also decreased the ratio of mitochondrial DNA to nuclear DNA in both ventricles. CONCLUSIONS: CH alters morphometry and function of mitochondria in the heart, but this effect is delayed in the right compared to the left ventricle, suggesting some adaptive processes at the onset of right ventricular hypertrophy.

Adenosine Triphosphatases↗
PubMed2003

Proinflammatory cytokines increase the rate of glycolysis and adenosine-5'-triphosphate turnover in cultured rat enterocytes.

OBJECTIVE: Measurements of steady-state adenosine-5'-triphosphate (ATP) levels in tissue samples from patients or experimental animals with sepsis or endotoxemia provide little information about the rate of ATP production and consumption in these conditions. Accordingly, we sought to use an in vitro "reductionist" model of sepsis to test the hypothesis that proinflammatory cytokines modulate ATP turnover rate. DESIGN: In vitro "reductionist" model of sepsis. SETTING: University laboratory. SUBJECTS: Cultured rat enterocyte-like cells. INTERVENTIONS: IEC-6 nontransformed rat enterocytes were studied under control conditions or following incubation for 24 or 48 hrs with cytomix, a mixture of tumor necrosis factor-alpha (10 ng/mL), interleukin-1beta (1 ng/mL), and interferon-gamma (1000 units/mL). To measure ATP turnover rate, ATP synthesis was acutely blocked by adding to the cells a mixture of 2-deoxyglucose (10 mM), potassium cyanide (8 mM), and antimycin A (1 microM). ATP content was measured at baseline (before metabolic inhibition) and 0.5, 1, 2, 5, and 10 mins later. Log-linear ATP decay curves were generated and the kinetics of ATP utilization thereby calculated. MEASUREMENTS AND MAIN RESULTS: ATP consumption rate was higher in cytomix-stimulated compared with control cells (3.11 +/- 1.39 vs. 1.25 +/- 0.66 nmol/min, respectively; p <.01). Similarly, the half-time for ATP disappearance was shorter in cytomix-stimulated compared with control cells (2.63 +/- 1.00 vs. 6.21 +/- 3.49; p <.05). In contrast to these findings, the rate of ATP disappearance was similar in cytokine-naïve and immunostimulated IEC-6 cells when protein and nucleic acid synthesis were inhibited by adding 50 microg/mL cycloheximide and 5 microg/mL actinomycin D to cultures for 4 hrs. The rates of glucose consumption and lactate production were significantly greater in cytomix-stimulated compared with controls cells. CONCLUSIONS: Incubation of IEC-6 cells with cytomix significantly increased ATP turnover. Increased ATP turnover rate was supported by increases in the rate of anaerobic glycolysis. These findings support the view that proinflammatory mediators impose a metabolic demand on visceral cells. In sepsis, cells may be more susceptible to dysfunction on the basis of diminished oxygen delivery and/or mitochondrial dysfunction.

Adenosine Triphosphate↗
PubMed2007

Inhibition of insulin secretion by cerulenin might be due to impaired glucose metabolism.

BACKGROUND: Cerulenin, an inhibitor of protein acylation, has been used as a tool to study the potential role of protein acylation in a variety of activities in different cells, and in stimulus-secretion coupling in pancreatic islets and clonal beta-cells. METHODS: In the present study we investigated its effects on stimulated insulin secretion, glucose metabolism and utilization, oxygen consumption and ATP levels. RESULTS: In isolated rat pancreatic islets, cerulenin pre-treatment (100 microM) inhibited insulin secretion in response to glucose, and to the non-hydrolysable analogue of leucine, aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH). These data are in accord with the hypothesis that protein acylation could be involved in the stimulation of insulin secretion. However, we also found that cerulenin profoundly decreased glucose oxidation, glucose utilization, oxygen consumption and ATP levels. Consequently, decreased metabolism provides an alternative mechanism to inhibition of protein acylation that could explain the inhibition of insulin secretion by cerulenin. CONCLUSIONS: Inhibition of insulin secretion by cerulenin can no longer be taken as evidence in favour of a role for protein acylation in the control of insulin release. As protein acylation is known to be involved in the normal functioning of proteins in stimulus-secretion coupling and exocytosis, more direct approaches to understand its role(s) are required.

Adenosine Triphosphate↗
PubMed1998

Direct effects of diazoxide on mitochondria in pancreatic B-cells and on isolated liver mitochondria.

1. The direct effects of diazoxide on mitochondrial membrane potential, Ca2+ transport, oxygen consumption and ATP generation were investigated in mouse pancreatic B-cells and rat liver mitochondria. 2. Diazoxide, at concentrations commonly used to open adenosine 5'-triphosphate (ATP)-dependent K+-channels (K(ATP) channels) in pancreatic B-cells (100 to 1000 microM), decreased mitochondrial membrane potential in mouse intact perifused B-cells, as evidenced by an increase of rhodamine 123 fluorescence. This reversible decrease of membrane potential occurred at non-stimulating (5 mM) and stimulating (20 mM) glucose concentrations. 3. A decrease of mitochondrial membrane potential in perifused B-cells was also caused by pinacidil, but no effect could be seen with levcromakalim (500 microM each). 4. Measurements by a tetraphenylphosphonium-sensitive electrode of the membrane potential of rat isolated liver mitochondria confirmed that diazoxide decreased mitochondrial membrane potential by a direct action. Pretreatment with glibenclamide (2 microM) did not antagonize the effects of diazoxide. 5. In Fura 2-loaded B-cells perifused with the Ca2+ channel blocker, D 600, a moderate, reversible increase of intracellular Ca2+ concentration could be seen in response to 500 microM diazoxide. This intracellular Ca2+ mobilization may be due to mitochondrial Ca2+ release, since the reduction of membrane potential of isolated liver mitochondria by diazoxide was accompanied by an accelerated release of Ca2+ stored in the mitochondria. 6. In the presence of 500 microM diazoxide, ATP content of pancreatic islets incubated in 20 mM glucose for 30 min was significantly decreased by 29%. However, insulin secretion from mouse perifused islets induced by 40 mM K+ in the presence of 10 mM glucose was not inhibited by 500 microM diazoxide, suggesting that the energy-dependent processes of insulin secretion distal to Ca2+ influx were not affected by diazoxide at this concentration. 7. The effects of diazoxide on oxygen consumption and ATP production of liver mitochondria varied depending on the respiratory substrates (5 mM succinate, 10 mM alpha-ketoisocaproic acid, 2 mM tetramethyl phenylenediamine plus 5 mM ascorbic acid), indicating an inhibition of respiratory chain complex II. Pinacidil, but not levcromakalim, inhibited alpha-ketoisocaproic acid-fuelled ATP production. 8. In conclusion, diazoxide directly affects mitochondrial energy metabolism, which may be of relevance for stimulus-secretion coupling in pancreatic B-cells.

Adenosine Triphosphate↗
PubMed2006

Folding on the chaperone: yield enhancement through loose binding.

A variety of small cageless chaperones have been discovered that can assist protein folding without the consumption of ATP. These include mini-chaperones (catalytically active fragments of larger chaperones), as well as small proteins such as alpha-casein and detergents acting as "artificial chaperones." These chaperones all possess exposed hydrophobic patches on their surface that act as recognition sites for misfolded proteins. They lack the complexity of chaperonins (that encapsulate proteins in their inner rings) and their study can offer insight into the minimal requirements for chaperone function. We use molecular dynamics simulations to investigate how a cageless chaperone, modeled as a sphere of tunable hydrophobicity, can assist folding of a substrate protein. We find that under steady-state (non-stress) conditions, cageless chaperones that bind to a single substrate protein increase folding yields by reducing the time the substrate spends in an aggregation-prone state in a dual manner: (a) by competing for aggregation-prone hydrophobic sites on the surface of a protein, hence reducing the time the protein spends unprotected in the bulk and (b) by accelerating folding rates of the protein. In both cases, the chaperone must bind to and hold the protein loosely enough to allow the protein to change its conformation and fold while bound. Loose binding may enable small cageless chaperones to help proteins fold and avoid aggregation under steady-state conditions, even at low concentrations, without the consumption of ATP.

Computer Simulation↗
PubMed1986

The sodium cycle. II. Na+-coupled oxidative phosphorylation in Vibrio alginolyticus cells.

The role of Na+ in Vibrio alginolyticus oxidative phosphorylation has been studied. It has been found that the addition of a respiratory substrate, lactate, to bacterial cells exhausted in endogenous pools of substrates and ATP has a strong stimulating effect on oxygen consumption and ATP synthesis. Phosphorylation is found to be sensitive to anaerobiosis as well as to HQNO, an agent inhibiting the Na+-motive respiratory chain of V. alginolyticus. Na+ loaded cells incubated in a K+ or Li+ medium fail to synthesize ATP in response to lactate addition. The addition of Na+ at a concentration comparable to that inside the cell is shown to abolish the inhibiting effect of the high intracellular Na+ level. Neither lactate oxidation nor delta psi generation coupled with this oxidation is increased by external Na+ in the Na+-loaded cells. It is concluded that oxidative ATP synthesis in V. alginolyticus cells is inhibited by the artificially imposed reverse delta pNa, i.e., [Na+]in greater than [Na+]out. Oxidative phosphorylation is resistant to a protonophorous uncoupler (0.1 mM CCCP) in the K+-loaded cells incubated in a high Na+ medium, i.e., when delta pNa of the proper direction [( Na+]in less than [Na+]out) is present. The addition of monensin in the presence of CCCP completely arrests the ATP synthesis. Monensin without CCCP is ineffective. Oxidative phosphorylation in the same cells incubated in a high K+ medium (delta pNa is low) is decreased by CCCP even without monensin. Artificial formation of delta pNa by adding 0.25 M NaCl to the K+-loaded cells (Na+ pulse) results in a temporary increase in the ATP level which spontaneously decreases again within a few minutes. Na+ pulse-induced ATP synthesis is completely abolished by monensin and is resistant to CCCP, valinomycin and HQNO. 0.05 M NaCl increases the ATP level only slightly. Thus, V. alginolyticus cells at alkaline pH represent the first example of an oxidative phosphorylation system which uses Na+ instead of H+ as the coupling ion.

Adenosine Triphosphatases↗