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PubMed1993

A role for the mitochondrial Na(+)-Ca2+ exchanger in the regulation of oxidative phosphorylation in isolated heart mitochondria.

The role of the Na(+)-Ca2+ exchanger of heart mitochondria in cellular functioning is not yet clear. The objectives of this study were to investigate the effects of stimulation and inhibition of the Na(+)-Ca2+ exchanger on the matrix free Ca2+ concentration in isolated heart mitochondria and to determine the consequences of these changes on the rate of NADH production via Krebs cycle turnover and the oxidative phosphorylation rate (OPR) supported by alpha-ketoglutarate dehydrogenase, a Ca(2+)-regulated matrix enzyme. Activation of Na(+)-Ca2+ exchange by increasing extramitochondrial Na+ concentration was found to decrease the matrix free [Ca2+] in a concentration-dependent manner. Inhibitors of mitochondrial Na(+)-Ca2+ exchange activity inhibited the decrease in matrix free [Ca2+] mediated by Na+. Increasing concentrations of Na+ were also found to inhibit both the rate of NADH production and OPR. Inhibitors of mitochondrial Na(+)-Ca2+ exchange also blocked the effects of Na+ on the rate of NADH production and OPR in a similar concentration range. The results indicate that alterations in matrix free [Ca2+] induced by changes in mitochondrial Na(+)-Ca2+ exchange activity are translated into changes in the rate of NADH production and the overall rate of oxidative phosphorylation.

Animals↗
PubMed1975

Protamine inhibition of the oxidative phosphorylation in intact, cytochrome c-depleted and restored mitochondria.

On the basis of polarographic data it is shown that protamine has a biphasic effect on the respiration of intact mitochondria. At lower protamine concentrations respiration is stimulated and this combined with a decrease of the respiratory control index; at higher ones respiration is inhibited and respiratory control is lost. In cytochrome c-depleted and restored mitochondria protamine effect on oxidative phosphorylation is only inhibitory. Increasing cytochrome c concentrations restore respiration in protamine-treated cytochrome c depleted mitochondria but not the respiratory control. Binding of cytochrome c to mitochondria is studied by determining from Scatchard plots the number of high affinity binding sites (n) and their stability constants (K). In absence of protamine in intact mitochondria n = 2.7 and K = 4.67-10(6) M-1; in cotochrome c depleted mitochondria n = 4.7 and K = 5.16-10(6) M-1. In both types of mitochondria protamine decreases significantly n as well as K. These data show that protamine may affect oxidative phosphorylation by causing desorption of cytochrome c from the inner mitochondrial membrane.

Adenosine Diphosphate↗
PubMed1985

Contribution of the translocator of adenine nucleotides and the ATP synthase to the control of oxidative phosphorylation and arsenylation in liver mitochondria.

The regulation of the rate of mitochondrial oxidative phosphorylation and arsenylation was studied at two external free Ca2+ concentrations. The rate of arsenate-stimulated respiration in absence of added ADP was not affected by external 10(-9) and 10(-6) M Ca2+ levels or carboxyatractyloside, while state 3 respiration was profoundly modified. In addition, the kinetic analysis showed that the rate of arsenylation in the presence of ADP was more efficient (Vm/Km ratio 3.5 times higher) in the catalytic process than phosphorylation. Therefore, this suggests that the activity of the ATP/ADP carrier is importantly controlled by Ca2+. The evaluation of the control in phosphorylation showed that the flux-control coefficients (Ci) exerted by the ATP/ADP carrier (ranged between 0.23 and 0.48) and the ATP synthase (0.05-0.57) were modified in a reciprocal way by Ca2+ and Pi concentrations. This suggests that these two enzymes are coupling sequentially through a common intermediate, the intramitochondrial ATP/ADP ratio. Other important steps controlling phosphorylation were the b-c1 complex (Ci = 0.30) and the cytochrome oxidase (Ci = 0.23) but they were not modified by Ca2+. It was also found that the main step controlling arsenylation was the ATP synthase (Ci = 0.74). The increment in the inorganic arsenate concentration induced a diminution in the control exerted by the ATP synthase (from 0.73 to 0.56). The results suggest that Ca2+ and Pi (or inorganic arsenate) could be regulated by ATP synthesis through an activating effect on ATP/ADP carrier and/or ATP synthase.

Adenosine Diphosphate↗
PubMed1997

Experimental evidence for dynamic compartmentation of ADP at the mitochondrial periphery: coupling of mitochondrial adenylate kinase and mitochondrial hexokinase with oxidative phosphorylation under conditions mimicking the intracellular colloid osmotic pressure.

Dextran M20 was added to isolated rat liver mitochondria to mimic cytosolic macromolecules. Under these conditions, the morphological changes in the mitochondrial periphery that occur upon isolation of the organelle are restored, i.e. the volume of the intermembrane space decreases and the contact site frequency increases. The ADP routing from mitochondrial kinases at various locations was investigated by using the activities of oxidative phosphorylation and externally added pyruvate kinase as sensors for ADP transport into the matrix and extramitochondrial compartment, respectively. The studies reveal that a significant fraction of the ADP generated by either adenylate kinase in the intermembrane space or by outer membrane bound hexokinase isozyme I, is not accessible to extramitochondrial pyruvate kinase. Quantitative information on the ADP compartmentation in rat liver mitochondria was obtained by comparing the ADP supply from mitochondrial kinases to oxidative phosphorylation with that of non-bound, extramitochondrially located kinases. This approach allowed us to estimate the ADP diffusion gradients which were present across the outer membrane and between the compartment formed by bound hexokinase and the extramitochondrial compartment. In the presence of 10% dextran M20 these ADP gradients amounted to approximately 12 microM. The possible role of mitochondrial kinases in ADP transport into mitochondria in vivo is discussed.

Adenosine Diphosphate↗
PubMed1991

Effect of aclarubicin and doxorubicin on rat liver mitochondrial oxidative phosphorylation.

The effects of Aclarubicin (aclacinomycin A; ACM) and Doxorubicin (adriamycin; ADM) on oxidative phosphorylation in rat liver mitochondria were studied in vitro. The state 3 oxygen uptake of mitochondria was reduced by only 2% by 20 microM of ADM, while the same concentration of ACM caused a 67% reduction. When 20 microM of ADM acted on state 4a oxygen uptake of mitochondria, only a slight decrease in state 3, state 4b, dinitrophenol-stimulated respiration and the respiratory control index was observed. In contrast 20 microM of ACM caused significant inhibition of all the above factors when compared with the controls. It was concluded that ACM has strong inhibitory action on the mitochondrial electron transfer system in vitro, and that one can expect functional failure of mitochondria to occur clinically during adverse response to the administration of this drug.

Aclarubicin↗
PubMed2004

Respiration, oxidative phosphorylation, and uncoupling protein in Candida albicans.

The respiration, membrane potential (Deltapsi), and oxidative phosphorylation of mitochondria in situ were determined in spheroplasts obtained from Candida albicans control strain ATCC 90028 by lyticase treatment. Mitochondria in situ were able to phosphorylate externally added ADP (200 microM) in the presence of 0.05% BSA. Mitochondria in situ generated and sustained stable mitochondrial Deltapsi respiring on 5 mM NAD-linked substrates, 5 mM succinate, or 100 microM N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride plus 1 mM ascorbate. Rotenone (4 microM) inhibited respiration by 30% and 2 micro M antimycin A or myxothiazole and 1 mM cyanide inhibited it by 85%. Cyanide-insensitive respiration was partially blocked by 2 mM benzohydroxamic acid, suggesting the presence of an alternative oxidase. Candida albicans mitochondria in situ presented a carboxyatractyloside-insensitive increase of Deltapsi induced by 5 mM ATP and 0.5% BSA, and Deltapsi decrease induced by 10 microM linoleic acid, both suggesting the existence of an uncoupling protein. The presence of this protein was subsequently confirmed by immunodetection and respiration experiments with isolated mitochondria. In conclusion, Candida albicans ATCC 90028 possesses an alternative electron transfer chain and alternative oxidase, both absent in animal cells. These pathways can be exceptional targets for the design of new chemotherapeutic agents. Blockage of these respiratory pathways together with inhibition of the uncoupling protein (another potential target for drug design) could lead to increased production of reactive oxygen species, dysfunction of Candida mitochondria, and possibly to oxidative cell death.

Candida albicans↗
PubMed1983

Effect of furosemide on mitochondrial electron transport system and oxidative phosphorylation.

The effects of furosemide on the mitochondrial electron transport system and on oxidative phosphorylation were explored. Furosemide above the concentration of 2 X 10(-3) mol/l was found to inhibit state 3 (ADP-dependent) respiration of the rat liver, renal cortex, renal medulla mitochondria. State 4 (resting) respiration was not affected by furosemide. Furosemide above the concentration of 7.5 X 10(-6) mol/l (substrate: glutamate-malate), and above 5 X 10(-6) mol/l (substrate: succinate) inhibited the respiration of rat liver mitochondria released by 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF 6847). This fact exactly indicates that furosemide inhibits the electron transport system in mitochondria. Furosemide at the concentration of 4 X 10(-3) mol/l inhibited the activities of NADH cytochrome c reductase and succinate cytochrome c reductase in sonicated mitochondrial subparticles of beef heart by 78.2% and 79.2% of control, respectively.

Animals↗
PubMed1977

Effect of dietary fats on oxidative phosphorylation and fatty acid profile of rat liver mitochondria.

Hydrogenated coconut oil or safflower seed oil were fed at 20% levels to weanling male albino rats for 2 months. The fatty acid patterns of the liver homogenates, mitochondria and the microsomes were determined by gas chromatography as were also the fatty acid patterns of the liver cholesterol esters and the phospholipids. The mitochondrial phospholipids were fractionated by thin layer chromatography and the fatty acid moieties of the individual phospholipids were screened on a gas chromatograph. The oxidative phosphorylation in the liver mitochondria was determined using glutamate, malate and succinate as substrates. The liver fatty acid pattern, especially that of the subcellular particles, seemed to be dependent upon the dietary fat. The fatty acid composition of the mitochondrial phospholipids varied with the dietary fat. Oxidative phosphorylation for glutamate and malate was higher in the group fed safflower oil compared to that in the group fed saturated fat; in the case of succinate, no such difference was noticed. These results suggest that the changes in the phosphorylation capacity are due to the changes in the mitochondrial phospholipids which reflect the composition of the dietary fat.

Animals↗
PubMed1988

Crystal violet as an uncoupler of oxidative phosphorylation in rat liver mitochondria.

Crystal violet exhibited characteristics of an uncoupler of oxidative phosphorylation, i.e. it released respiratory control, hindered ATP synthesis, enhanced ATPase activity, and produced swelling of isolated rat liver mitochondria. Maximal stimulation of respiration, ATPase activity, and swelling was observed at a concentration of 40 microM. The inhibition of State 3 respiration by oligomycin was released by crystal violet. High concentrations of crystal violet inhibited mitochondrial respiration. The uncoupling effect of crystal violet required inorganic phosphate and was abolished by N-ethylmaleimide. The adenine nucleotides ADP and ATP protected mitochondria from uncoupling by the dye. The dye taken up by mitochondria was released into the incubation medium on induction of uncoupling. In the absence of phosphate, the dye did not cause uncoupling, but its retention was much greater than in the presence of phosphate. Crystal violet is suggested to induce uncoupling by acting on the membrane, rather than by its electrophoretic transfer into the mitochondria.

2,4-Dinitrophenol↗
PubMed1977

The kinetic mechanism of action of an uncoupler of oxidative phosphorylation.

The chemiosmotic hypothesis predicts that the mechanism by which weak acids uncouple oxidative phosphorylation in mitochondria is identical to the mechanism by which they transport hydrogen ions across artificial bilayer membranes. We report here the results of a kinetic study of uncoupler-mediated hydrogen ion transport across bilayer membranes. We made electrical relaxation measurements on black lipid membranes exposed to the substituted benzimidazole 5,6-dichloro-2-trifluoromethylbenzimidazole. The simplest model consistent with our experimental data allowed us to deduce values for adsorption coefficients and rate constants. Our major conclusions are that the back diffusion of the neutral species is the rate limiting step for the steady state transport of hydrogen ions, that both the neutral and charged forms of the uncoupler adsorb strongly to the interfaces, and that the reactions at the membrane-solution interfaces occur sufficiently rapidly for equilibrium to be maintained. Independent measurements of the adsorption coefficients of both the neutral and anionic forms of the weak acid and also of the permeability of the membrane to the neutral form agreed well with the values deduced from the kinetic study.

Benzimidazoles↗
PubMed1978

Evaluation of oxidative phosphorylation in hearts from euthyroid, hypothyroid, and hyperthyroid rats.

The energy relationships between cytosolic and mitochondrial metabolism were studied in the hearts from euthyroid, hypothyroid, and hyperthyroid rats. Isolated mitochondria showed high respiratory control ratios and impermeability to exogenous NADH. Hypo- and hyperthyroidism, respectively, resulted in lower and higher contents of both cytochromes per mitochondrion and mitochondrial protein per gram of wet weight of heart without changes in the ratio of cytochrome c to cytochrome aa3. In isolated perfused heart, the hyperthyroid state led to an increase in work rate and thereby an elevation of Vo2, which resulted in an increase oxidation-reduction turnover number for the cytochromes. An agreement was found between [ATP]/[ADP][Pi] of cytosolic free adenine nucleotides and the value calculated from a mathematical model of mitochondrial respiration. This implies that mitochondrial respiration is controlled at the cytochrome oxidase reaction and that oxidative phosphorylation in intact tissue is tightly coupled irrespective of thyroid state. It is concluded that thyroid hormone causes an increase in the mitochondrial mass, mitochondrial cytochrome content, and respiratory rate, and consequently expands the capacity of oxidative metabolism without an uncoupling effect on oxidative phosphorylation.

Adenine Nucleotides↗
PubMed1985

Effects of thyroid hormone on mitochondrial oxidative phosphorylation.

In order to locate sites of action of thyroid hormone on mitochondrial oxidative phosphorylation we have used an experimental application of control analysis as previously described [Groen, Wanders, Westerhoff, Van der Meer & Tager (1982) J. Biol. Chem. 257, 2754-2757]. Rat-liver mitochondria were isolated from hypothyroid rats or from hypothyroid rats 24 h after treatment with a single dose of 3,3',5-triiodothyronine (T3). The amount of control exerted by four different steps on State-3 respiration with succinate as respiratory substrate was quantified by using specific inhibitors. The hormone treatment resulted in an increase in the flux control coefficient of the adenine nucleotide translocator, the dicarboxylate carrier and cytochrome c oxidase and a decrease in the flux control coefficient of the bc1-complex. The results of this analysis indicate that thyroid hormone treatment results in an activation of the bc1-complex and of at least one other enzyme, possibly succinate dehydrogenase. Measurement of the extramitochondrial ATP/ADP ratio at different rates of respiration (induced by addition of different amounts of hexokinase in the presence of glucose and ATP) showed that the adenine nucleotide translocator operates at a higher (ATP/ADP)out after T3 treatment, which supports previous reports on stimulation of this step by thyroid hormone.

Adenosine Diphosphate↗
PubMed1986

Fatty acid uncoupling of oxidative phosphorylation in rat liver mitochondria.

Free fatty acids (FFA) are known to uncouple oxidative phosphorylation in mitochondria. However, their mechanism of action has not been elucidated as yet. In this study we have investigated in detail the patterns of uncoupling by the FFA oleate and palmitate in rat liver mitochondria and submitochondrial particles. The patterns of uncoupling by FFA were compared to uncoupling induced by the ionophores valinomycin (in the presence of K+) and gramicidin (in the presence of Na+) and the proton translocator carbonyl cyanide m-chlorophenylhydrazone (CCCP). The most striking difference in the pattern of uncoupling relates to the effect on the proton electrochemical potential gradient, delta mu H. Uncoupling by ionophores, particularly valinomycin, is associated with and most likely caused by a major reduction of delta mu H. In contrast, uncoupling by FFA is not associated with a significant reduction of delta mu H, indicating another mechanism of uncoupling. We suggest the use of the term decouplers for uncoupling agents such as FFA and general anesthetics that do not collapse the delta mu H [Rottenberg, H. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 3313-3317]. The protonophore CCCP and to some extent the ionophore gramicidin indicate a mixed mode of uncoupling since their effect on delta mu H is moderate when compared to that of valinomycin. Another distinguishing feature of uncouplers that collapse the delta mu H is their ability to stimulate ADP-stimulated respiration (state 3) further. Decouplers such as FFA and general anesthetics do not stimulate state 3 respiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Uncoupling of oxidative phosphorylation. 2. Alternative mechanisms: intrinsic uncoupling or decoupling?

The mechanism of uncoupling of oxidative phosphorylation by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP), oleic acid, and chloroform is further investigated by measuring in the presence of a certain concentration of each type of uncoupler (i) the mitochondrial P/O and respiratory control ratios upon progressive inhibition of the redox pumps and (ii) delta mu H and the rate of either electron transfer or adenosine 5'-triphosphate (ATP) hydrolysis in static head upon progressive inhibition of either the redox or the adenosine triphosphatase (ATPase) proton pumps. Chloroform exhibits in all the experiments a behavior very different from that of FCCP and oleic acid. For example, upon addition of antimycin to chloroform-supplemented mitochondria, the respiratory control ratio remains unchanged and the P/O ratio slightly increases (in a certain range of inhibition) instead of decreasing as expected for an increased membrane conductance (and as indeed measured in the presence of either FCCP or oleic acid). From the kinetic model of chemiosmotic free energy coupling described by Pietrobon and Caplan [Pietrobon, D., & Caplan, S.R. (1986) Biochemistry 25, 7690-7696] all the results can be simulated by making the assumptions that (i) chloroform acts specifically at the level of the proton pumps and intrinsically uncouples electron transfer and ATP hydrolysis/synthesis from proton translocation and (ii) FCCP and oleic acid have a mixed behavior and act both as protonophores and as intrinsic uncouplers of the redox pumps (but not of the ATPases). The consistency of the results with the alternative hypothesis that the three agents interfere either with localized energy coupling sites or with a direct interaction between proton pumps is discussed.

Adenosine Triphosphatases↗
PubMed1995

Modulation of GLUT1 intrinsic activity in clone 9 cells by inhibition of oxidative phosphorylation.

Brief (1-2 h) exposure of Clone 9 cells to inhibitors of oxidative phosphorylation such as azide is known to markedly increase glucose uptake. Clone 9 cells express GLUT1 but not GLUT2, -3, and -4, and the azide effect was not accompanied by any increase in cellular or plasma membrane GLUT1 level. To identify the molecular event underlying this apparent increase in GLUT1 intrinsic activity, we studied the acute effects of azide on the substrate binding activity of GLUT1 in Clone 9 cells by measuring glucose-sensitive cytochalasin B binding. The glucose-displaceable, cytochalasin B binding activity was barely detectable in membranes isolated from Clone 9 cells under control conditions but was readily detectable after a 60-min incubation of cells in the presence of 5 mM azide showing a 3-fold increase in binding capacity with no change in binding affinity. Furthermore, the cytochalasin B binding activity of purified human erythrocyte GLUT1 reconstituted in liposomes was significantly reduced in the presence of cytosol derived from azide-treated Clone 9 cells but not in the presence of cytosol from control cells; this effect was heat-labile and abolished by the presence of the peptide corresponding to the GLUT1 COOH-terminal sequence. These results suggest that a cytosolic protein in Clone 9 cells binds to GLUT1 at its COOH-terminal domain and inhibits its substrate binding and that azide-induced metabolic alteration releases GLUT1 from this inhibitory interaction. Studying the binding of cytosolic proteins derived from 35S-labeled Clone 9 cells to glutathione S-transferase fusion protein containing glucose transporter COOH-terminal sequences, we identified 28- and 70-kDa proteins that bind specifically to the cytoplasmic domain of GLUT1 and GLUT4 in vitro. We also found a 32P-labeled, 85-kDa protein that binds to GLUT4 but not to GLUT1 and only in cytosol derived from azide-treated cells. The roles, if any, of these glucose transporter-binding proteins in the azide-sensitive modulation of GLUT1 substrate binding activity in Clone 9 cells are yet to be determined.

Animals↗
PubMed1989

Effects of sesquiterpene lactones on mitochondrial oxidative phosphorylation.

1. The toxic plant sesquiterpene lactones, helenalin, hymenoxon, mexicanin-E, tenulin, dihydrogriesenin, and psilotropin which were isolated from Helenium, Hymenoxys, and Geigeria spp markedly inhibited "state 3" respiration in mouse hepatic mitochondria. With the exception of dihydrogriesenin and psilotropin, all the other sesquiterpene lactones stimulated "state 4" respiration. 2. The sesquiterpene lactones also stimulated ATPase activity in the presence of Mg2+ ions and caused mitochondrial swelling in buffer solutions containing magnesium, sodium, ammonium and potassium chloride salts. 3. The number of alkylating sites present in a sesquiterpene lactone appears to be related to the inhibitory activity on mitochondrial oxidative phosphorylation, however, the structure-activity relationship of these lactones is not clear at present. 4. Mitochondria prepared from the liver of ethoxyquin hydrochloride-fed mice were less susceptible to sesquiterpene lactone-mediated inhibition of mitochondrial oxidative phosphorylation.

Adenosine Triphosphatases↗
PubMedDate not supplied

The disturbance of oxidative phosphorylation in rat liver mitochondria by the carcinogens 12-hydroxystearic acid and its methyl ester.

In a search to determine common molecular features in potential carcinogenic dietary fatty acids, Swern et al. (1970) found that 12-hydroxystearic acid and its methyl ester were carcinogenic. This was surprising to Swern et al. (1970) and Van Duuren et al. (1972), as it was not readily apparent how such agents could be converted to alkylating agents. We have observed that the carcinogens 12-hydroxystearic acid and its methyl ester disrupted oxidative phosphorylation in rat liver mitochondria. The in vitro mitochondrial effects induced by the agents included: a) uncoupled respiration, b) ATPase activity, c) energized volume changes linked either to respiration or ATP. Mitochondria mediated the enzymic conversion of the ester to the acid. Conversion was retarded by the thiol reagent showdomycin. These data in conjuction with our previous reports dealing with other carcinogens and their derivatives contribute to an experimental confluence between oxidative phosphorylation and chemical carcinogenesis.

Adenosine Triphosphatases↗
PubMed2003

Circadian rhythms of oxidative phosphorylation: effects of rotenone and melatonin on isolated rat brain mitochondria.

Mitochondrial experiments are of increasing interest in different fields of research. Inhibition of mitochondrian activities seems to play a role in Parkinson's disease and in this regard several animal models have used inhibitors of mitochondrial respiration such as rotenone or MPTP. Most of these experiments were done during the daytime. However, there is no reason for mitochondrial respiration to be constant during the 24 h. This study investigated the circadian variation of oxidative phosphorylation in isolated rat brain mitochondria and the administration-time-dependent effect of rotenone and melatonin. The respiratory control ratio, state 3 and state 4, displayed a circadian fluctuation. The highest respiratory control ratio value (3.01) occurred at 04:00 h, and the lowest value (2.63) at 08:00 h. The highest value of state 3 and state 4 oxidative respiration occurred at 12:00 h and the lowest one at 20:00 h. The 24 h mean decrease in the respiratory control ratio following incubation with melatonin and rotenone was 7 and 32%, respectively; however, the exact amount of the inhibition exerted by these agents varied according to the time of the mitochondria isolation. Our results show the time of mitochondrial isolation could lead to interindividual variability. When studies require mitochondrial isolation from several animals, the time between animal experiments has to be minimized. In oxidative phosphorylation studies, the time of mitochondria isolation must be taken into account, or at least specified in the methods section.

Animals↗