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[Phospholipid composition and oxidative phosphorylation in liver mitochondria in hepatitis].

Phospholipid composition and oxidative phosphorylation were studied in liver mitochondria of rats with experimental chronic hepatitis. The hepatitis was simulated by means of two hepatotropic drugs--heliotrin and CCl4. Content of phosphatidyl inositol was decreased and that of phosphatidic acid--increased in the hepatitis independently of the nature of the agent inducing the disease. At the same time, content of lysophosphatidyl ethanolamine was decreased but content of lysocardiolipine and lysophosphatidic acid was increased. In CCl4-induced hepatitis content of cardiolipine and sphingomyelin was decreased, whereas after the treatment with heliotrin content of cardiolipine in liver tissue was unaltered and that of sphingomyelin was increased. Content of lysophosphatidyl choline was considerably increased in CCl4-hepatitis but it was only slightly altered after the treatment with heliotrin. The most pronounced alterations in the phospholipid spectrum and oxidative phosphorylation were found in liver mitochondria in the CCl4-induced hepatitis.

Animals↗
PubMed1980

Substrate level versus oxidative phosphorylation in the generation of ATP in Thiobacillus denitrificans.

Particulate fractions of Thiobacillus denitrificans catalyse that the phosphorylation of ADP to ATP during the oxidation of various inorganic sulphur compounds or NADH via an electron transport chain. On the other hand, a "soluble" cell-free fraction synthesized ATP from APS and inorganic phosphate. The production of ATP was verified either by the firefly luciferin-luciferase enzyme system or by the incorporation of 32Pi into ATP. During the oxidation of sulphide, sulphite and NADH the production of ATP from ADP by particulate fractions is inhibited by compounds that inhibit electron transfer and by uncouplers of oxidative phosphorylation. However, these compounds had little effect on the production of ATP from AMP during the oxidation of sulphite by the soluble fraction. NADH was the most effective electron donor for oxidative phosphorylation. The soluble fraction contained high activities of ATP sulphurylase, inorganic pyrophosphatase and adenylate kinase but ADP sulphurylase activity was relatively low. The effects of inhibitors on ATP production from APS and Pi are compared with those on adenylate kinase and ATP sulphurylase.

Adenosine Diphosphate↗
PubMed1996

Alcohol inhibits the depolarization-induced stimulation of oxidative phosphorylation in synaptosomes.

The effects of alcohol and Ca2+ transport inhibitors on depolarization-induced stimulation of oxidative phosphorylation and free-Ca2+ concentrations in rat synaptosomes were investigated. Glucose oxidation was stimulated by depolarization with K+ or veratridine and by the Ca2+ ionophore ionomycin. The stimulation by K+, veratridine, and ionomycin was correlated with elevation of synaptosomal free Ca2+. Depolarization-stimulated respiration was inhibited by verapamil, Cd2+, and ruthenium red but not by diltiazem. Synaptosomal Ca2+ elevation was inhibited by verapamil but not by ruthenium red. These results indicate that the stimulation depends on elevation of mitochondrial free Ca2+. Ethanol, at pharmacological concentrations (50-200 mM), inhibited the Ca2+-dependent stimulation of oxidative phosphorylation. This inhibition resulted, in part, from the inhibition of voltage-gated Ca2+ channels, which inhibited the elevation of synaptosomal free Ca2+, and, in part, from the stimulation of the mitochondrial Ca2+/Na+ antiporter, which inhibited the elevation of the mitochondrial matrix free Ca2+. The inhibition by ethanol of the excitation-induced stimulation of oxidative phosphorylation in the synapse may contribute to the depressant and narcotic effects of alcohol and enhance excitotoxicity.

Adenosine Triphosphate↗
PubMed2004

Iron uncouples oxidative phosphorylation in brain mitochondria isolated from vitamin E-deficient rats.

Few, if any, studies have examined the effect of vitamin E deficiency on brain mitochondrial oxidative phosphorylation. The latter was studied using brain mitochondria isolated from control and vitamin E-deficient rats (13 months of deficiency) after exposure to iron, an inducer of oxidative stress. Mitochondria were treated with iron (2 to 50 microM) added as ferrous ammonium sulfate. Rates of state 3 and state 4 respiration, respiratory control ratios, and ADP/O ratios were not affected by vitamin E deficiency alone. However, iron uncoupled oxidative phosphorylation in vitamin E-deficient mitochondria, but not in controls. In vitamin E-deficient mitochondria, iron decreased ADP/O ratios and markedly stimulated state 4 respiration; iron had only a modest effect on these parameters in control mitochondria. Thus, vitamin E may have an important role in sustaining oxidative phosphorylation. Low concentrations of iron (2 to 5 microM) oxidized mitochondrial tocopherol that exists in two pools. The release of iron in brain may impair oxidative phosphorylation, which would be exacerbated by vitamin E deficiency. The results are important for understanding the pathogenesis of human brain disorders known to be associated with abnormalities in mitochondrial function as well as iron homeostasis (e.g., Parkinson's disease).

Animals↗
PubMed1989

[The effect of smoking and alcohol on oxidative phosphorylation in mitochondria in the myocardium].

The simultaneous effect of passive smoking and alcohol on oxidative phosphorylation was studied in rabbits after 14 day exposure. The results were compared with those obtained in previous studies on the isolated noxious effect of smoking or alcohol. The authors conclude that under the given experimental conditions the combined effect of ethanol and smoking doses not affect oxidative phosphorylation of mitochondria: energy production and respiration of mitochondria were preserved. The protective effect of ethanol upon the harmful effect of smoking on mitochondrial oxidative phosphorylation is accounted for by potential interaction of nicotine and ethanol in the microsomal fraction of the liver.

Animals↗
PubMed1975

[Oxidative phosphorylation, catecholamine content and contractile function of the myocardium in patients with acquired heart defects, operated on under artificial circulation].

A simultaneous determination of oxidative phosphorylation, catecholamines content and contractile function of the myocardium was conducted in patients with acquired heart diseases operated under extracorporeal circulation. The degree of conjugation of the oxidative phosphorylation has been found to depend on the severity of the initial state of the patient, and on the conditions of the surgical intervention: duration of cardiopulmonary by-pass before the excision of the mitral valve, duration of cross-clamping of the aorta, and the temperature regiment of the perfusion. Besides, it has been found that the conjugated oxidative phosphorylation is associated with the presence of catecholamines in the myocardium, while the dissociation of these processes is accompanied by a sharp fall in the content of adrenalin, noradrenalin and dophamine. The established parallelism of the catecholamines content and the oxidative phosphorylation indicates the existing correlation between them, which may determine the character of the contractile function of the myocardium.

Adenosine Triphosphate↗
PubMed2006

Profound effects of the general anesthetic etomidate on oxidative phosphorylation without effects on their yield.

We investigated the effects of the general anesthetic Etomidate on oxidative phosphorylation in isolated rat liver mitochondria. The study of each electron transfer site shows that there is an inhibition: mainly at complex I but also, to a lesser extent, at complex III. Moreover, with succinate as substrate, the increase in non-phosphorylating respiration is accompanied by a decrease in DeltaPsi. However, this effect is not due to classical uncoupling of oxidative phosphorylation, since ADP addition at high Etomidate concentrations restores the transmembrane difference of electrical potential. Also, in the same range of Etomidate concentration, the ATP/O ratio is not significantly affected. In conclusion, the main effect of Etomidate is to decrease the oxidative phosphorylation rate without changing yield. The H(+) leak which appears under non-phosphorylating conditions becomes negligible in physiological conditions.

Adenosine Diphosphate↗
PubMed1989

Effect of verapamil on phosphate-induced changes in oxidative phosphorylation and atractyloside-sensitive adenine nucleotide translocase activity in two populations of rat heart mitochondria.

Phosphate (Pi)-induced depression in cardiac mitochondrial function was studied using mitochondria isolated by two different procedures which purportedly yield two distinct populations. Subsarcolemmal mitochondria (SLM) exhibited an enhanced sensitivity to 20 mM Pi with respect to oxidative phosphorylation. Thus, a significant depression in oxidative phosphorylation in this population was seen following only 1-min treatment, whereas interfibrillar mitochondria (IFM) were unaffected. Both populations showed a similar response to 5-min treatment with Pi. The Pi-induced depression in respiration was partially, although significantly, reversed by a 50 microM concentration of the calcium antagonist verapamil, an observation which suggests a contribution of calcium to the Pi-induced defect in respiration. Pi also produced a potent inhibition of ADP uptake in both mitochondrial populations, which was in close agreement to Pi-induced modification of low amplitude shrinkage-swelling responses following ADP addition. Both of these parameters were unaffected by verapamil. Our results show an enhanced sensitivity of SLM to a verapamil-sensitive Pi-induced depression in oxidative phosphorylation. However, the potent, verapamil-insensitive decrease in adenine nucleotide translocase activity by Pi demonstrates that calcium is likely only partially involved in Pi-induced depression in oxidative phosphorylation and that a further partial contribution arises from a decrease in adenine nucleotide translocase activity.

Adenosine Diphosphate↗
PubMed2002

Seizure-dependent modulation of mitochondrial oxidative phosphorylation in rat hippocampus.

Mitochondrial function is a key determinant of both excitability and viability of neurons. Here, we demonstrate seizure-dependent changes in mitochondrial oxidative phosphorylation in the epileptic rat hippocampus. The intense pathological neuronal activity in pilocarpine-treated rats exhibiting spontaneous seizures resulted in a selective decline of the activities of NADH-CoQ oxidoreductase (complex I of the respiratory chain) and cytochrome c oxidase (complex IV of respiratory chain) in the CA3 and CA1 hippocampal pyramidal subfields. In line with these findings, high-resolution respirometry revealed an increased flux control of complex I on respiration in the CA1 and CA3 subfields and decreased maximal respiration rates in the more severely affected CA3 subfield. Imaging of mitochondrial membrane potential using rhodamine 123 showed a lowered mitochondrial membrane potential in both pyramidal subfields. In contrast to the CA1 and CA3 subfields, mitochondrial oxidative phosphorylation was unaltered in the dentate gyrus and the parahippocampal gyrus. The changes of oxidative phosphorylation in the epileptic rat hippocampus cannot be attributed to oxidative enzyme modifications but are very likely related to a decrease in mitochondrial DNA copy number as shown in the more severely affected CA3 subfield and in cultured PC12 cells partially depleted of mitochondrial DNA. Thus, our results demonstrate that seizure activity downregulates the expression of mitochondrial-encoded enzymes of oxidative phosphorylation. This mechanism could be invoked during diverse forms of pathological neuronal activity and could severely affect both excitability and viability of hippocampal pyramidal neurons.

Animals↗
PubMed1997

Effect of prolonged hypothermic ischemia and reperfusion on oxygen consumption and total mechanical energy in rat myocardium: participation of mitochondrial oxidative phosphorylation.

BACKGROUND: To reduce ischemia-reperfusion injury of hearts in open heart surgery and transplantation, it is important to know the critical period of ischemia in which donor hearts can sustain their function satisfactorily. Cardiac function has been deduced from oxygen consumption (VO2) and mechanical parameters such as pressure-volume area (PVA). Inhibited mitochondrial oxidative phosphorylation during ischemia indicates that ATP production is uncoupled from VO2. Therefore, both mitochondrial oxidative phosphorylation and total mechanical energy should be examined to evaluate cardiac function after ischemia and reperfusion. METHODS: Isolated rat hearts were stored in Euro-Collins solution at 4 degrees C for 8, 12, and 24 hr and reperfused in a working mode with a modified Krebs-Henseleit bicarbonate solution. PVA and VO2 were examined in isovolumic contraction, and ventricular contractility and total mechanical energy were assessed, respectively, by the end-systolic elastance (Ees) and PVA. Mitochondrial oxidative phosphorylation in the presence of succinate and mitochondrial lipid peroxide levels were estimated in similarly treated rat hearts. RESULTS: Ees was decreased by ischemia without significant difference. The VO2 to PVA ratio remained linear, although VO2 at null PVA and the VO2 to PVA ratio significantly increased after 12 hr of ischemia. Mitochondrial oxidative phosphorylation was decreased significantly by reperfusion after 12 hr of ischemia. Mitochondrial lipid peroxide levels were increased significantly after 12 hr of ischemia. CONCLUSIONS: In isolated rat hearts, decreased efficiency for energy conversion from consumed oxygen to cardiac performance occurs between 8 and 12 hr of hypothermic ischemia, which was coincident with disturbed mitochondrial oxidative phosphorylation, to which lipid peroxidation may contribute.

Animals↗
PubMed1963

INHIBITION OF OXIDATIVE PHOSPHORYLATION IN ESCHERICHIA COLI BY DIHYDROSTREPTOMYCIN.

Bragg, P. D. (University of British Columbia, Vancouver, B.C., Canada), and W. J. Polglase. Inhibition of oxidative phosphorylation in Escherichia coli by dihydrostreptomycin. J. Bacteriol. 86:1236-1240. 1963.-Dihydrostreptomycin inhibited the oxidation of succinate in extracts of antibiotic-sensitive Escherichia coli. The inhibitable reaction required both the particulate and the supernatant fractions from sonic extracts which had been centrifuged at 100,000 x g. Dihydrostreptomycin was found to inhibit phosphorylation coupled with the oxidation of reduced nicotinamide adenine dinucleotide (NADH). The inhibition of oxidative phosphorylation by dihydrostreptomycin appeared to precede the effect of the antibiotic on oxidation. The streptomycin antagonist, 2-heptyl-4-hydroxyquinoline N-oxide, inhibited the oxidation of succinate and of NADH, but showed little effect on oxidative phosphorylation. Oxidative phosphorylation was not affected by dihydrostreptomycin in strains of E. coli which were antibiotic-resistant or -dependent.

Anti-Bacterial Agents↗
PubMed2003

Influence of substrate activation (hydrolysis of ATP by first steps of glycolysis and beta-oxidation) on the effect of enzyme deficiencies, inhibitors, substrate shortage and energy demand on oxidative phosphorylation.

In intact tissues respiratory substrates (glucose, fatty acids) must be activated with the use of ATP before they may be oxidised and used for energy (ATP) production. This activation by product constitutes an example of a typical positive feedback. In the present paper, the influence of substrate activation on the effect of inborn enzyme deficiencies, inhibitors, lowered oxygen tension, respiratory fuel shortage and increased energy demand on respiration and ATP synthesis is studied with the aid of the dynamic computer model of oxidative phosphorylation in isolated mitochondria developed previously. Computer simulations demonstrate that, in the case where oxidative phosphorylation in the whole organism is partially inhibited, the necessity of substrate activation can have significant impact on the relationship between the activity of (particular steps of) oxidative phosphorylation (or the value of energy demand) and the respiration rate. Depending on the sensitivity of ATP usage to ATP concentration, substrate activation may either slightly enhance the effect of the decrease in the oxidative phosphorylation activity (increase in energy demand) or may lead to a non-stability and sudden collapse of the respiration rate and phosphorylation potential below (above) a certain threshold value of oxidative phosphorylation activity (energy demand). This theoretical finding suggests a possible causal relationship between the affinity of ATP usage to [ATP] and the tissue specificity of mitochondrial diseases.

Adenosine Triphosphate↗
PubMed1980

Urea cycle regulation: I. Coupling of ornithine metabolism to mitochondrial oxidative phosphorylation.

Ornithine metabolism is coupled to oxidative phosphorylation in isolated rat liver mitochondria. The pathway involving ornithine: alpha-ketoglutarate transaminase (OKT), glutamic semialdehyde dehydrogenase (GSDH), and glutamate dehydrogenase (GDH) with cycling of alpha-ketoglutarate-glutamate at the OKT reaction appears to be involved. Ornithine may be utilized by this pathway to sustain ATP levels during mitochondrial energy-deficiency states with resultant decreased urea-cycle flux and increased ammonia production. This pathophysiologic mechanism suggests that hyperammonemia is a consequence of an energy-deficiency state. Therapy directed toward alleviating the energy-deficiency state may be more beneficial than efforts to reduce ammonia levels.

Adenosine Triphosphate↗
PubMed1984

A coulombic hypothesis of mitochondrial oxidative phosphorylation.

A coulombic hypothesis of mitochondrial oxidative phosphorylation is presented, founded upon the evidence for negative fixed charge formation during electron transport chain activity. The intermediary force is electrostatic (psi H) and not electrochemical (delta mu H). The electrochemical potential of the chemiosmotic hypothesis is identified as a "phantom" parameter which owes its delusive existence to the procedures by which it is measured. The connection between psi H and the conditional delta mu H values is examined; it entails the use of a variable conversion factor, f, where delta mu H (mV) = f psi H, and the concept of the "protonic status" of the diffuse double layer. A number of problems which beset the chemiosmotic view are reappraised in the light of the new interpretation, and find authentic solutions.

Adenosine Triphosphate↗
PubMed1974

Studies of respiratory components and oxidative phosphorylation in mitochondria of mi-1 Neurospora crassa.

Oxidative phosphorylation has been demonstrated with mitochondria of the mi-1 respiratory mutant of Neurospora crassa. The P/O ratios observed with these mitochondria were approximately 0.8 with citrate and 0.4 with either externally added reduced nicotinamide adenine dinucleotide (NADH), succinate, or ascorbate-tetramethyl-p-phenylenediamine (TPD). These P/O ratios suggest that there are only two sites of phosphorylation in mitochondria isolated from young (20 to 24 h) cultures of the mi-1 mutant. The energy-dependent reduction of NAD(+) with succinate and the phosphorylation associated with ascorbate-TPD oxidation indicate that the first and the third sites of energy coupling are present in this mutant. Difference spectra of mitochondria from young cultures of the mi-1 mutant revealed the presence of cytochrome c. Cytochromes b and a + a(3) were not detected. However, in the presence of antimycin A, a small peak in the Soret region at 430 nm was observed. A carbon monoxide difference spectrum revealed the presence of a component of the respiratory chain with a spectrum similar to that of cytochrome o. It is of interest that respiratory inhibitors such as antimycin A, 2-n-nonylhydroxyquinoline N-oxide, and cyanide abolished phosphorylation but only partially inhibited oxidation. It is postulated that the mi-1 respiratory system contains two pathways of electron transport-the first is associated with a phosphorylating pathway, whereas the second is a non-phosphorylating electron transport pathway.

Antimycin A↗
PubMed1976

Molecular polymorphism and mechanisms of activation and deactivation of the hydrolytic function of the coupling factor of oxidative phosphorylation.

The 13S coupling factor of oxidative phosphorylation from Alcaligenes faecalis has a latent adenosine triphosphatase (ATPase) function that can be activated by heating at 55 degrees C for 10 min at pH 8.5 in 50% glycerol. The specific activity increases from 0.1 to 20--30 mumol min-1 mg-1. Adenosine 5'-triphosphate (ATP) is not required for stabilization at 55 degreesC when glycerol is present. Activation involves displacement of the endogenous ATPase inhibitor subunit (epsilon subunit), and readdition of this subunit results in deactivation. In the deactivation process the ATPase inhibitor subunit can be replaced by other cationic proteins such as protamine, histones, or poly(lysine). Mg2+ and H+ also are effective deactivators. The fact that every positively charged substance tested deactivated the enzyme suggests that the inhibitor subunit is complexed with the enzyme at a site containing a surplus of negative charges. The activated enzyme is not labile, but it is salt labile, having a half-life of 2-3 min in 0.1 M KI at either 25 or 0 degrees C. The activated ATPase is also inhibited by aurovertin, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD), and by the cross-linking agent dimethyl suberimidate. Evidence for polymorphism comes from finding that the properties of the unactivated enzyme (intrinsic ATPase) are different in many ways from the properties of activated ATPase. With respect to the coupling factor's ability to hydrolyze ATP, the data in this study suggest that there are at least four distinct functional allomorphs of this enzyme: (1) the latent enzyme, which has no kinetically measurable ATPase activity, (2) intrinsic ATPase, which is catalyzed by a small percentage of the molecular population that has been activated by some natural mechanism, (3) activated ATPase, which has properties different from those of intrinsic ATPase, and (4) aged activated ATPase, in which some of the properties (Km for substrate, sensitivity to deactivation by Mg2+ and H+) spontaneously change within 30 min.

Adenosine Triphosphatases↗
PubMed1975

Effect of aflatoxins on oxidative phosphorylation by rat liver mitochondria.

The in vitro effect of aflatoxins M1, B1 and G1 on oxidative phosphorylation by rat liver mitochondria with succinate as substrate has been studied. All these toxins inhibit the electron transport chain at a 1-10-4 M concentration and the site of inhibition is between cytochrome b and cytochrome c or c1. Aflatoxin M1 (AFM1) uncouples oxidative phosphorylation at a concentration of 1-10-6 M and reduces the ADP:O ratio, whereas aflatoxin B1 (AFB1) at 1-10-6 M concentration uncouples oxidative phosphorulation but does not affect the ADP:O ratio. At a concentration of 1-10-5 M, AFB1 also decreases the ADP:O ratio along with the uncoupling of oxidative phosphorylation. Aflatoxin G1 (AFG1) acts as an uncoupler at a relatively higher concentration of 1-10-4 M. Preincubation of mitochondria with these aflatoxins resulted in inhibition of respiration and uncoupling of rat liver mitochondria.

Adenosine Diphosphate↗