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Source of the oxygen atoms of nitrate in the oxidation of nitrite by Nitrobacter agilis and evidence against a P-O-N anhydride mechanism in oxidative phosphorylation.

15N, 18O Tracer studies were applied to the aerobic oxidation of nitrite to nitrate by the chemolithotrophic bacterium, Nitrobacter agilis. It was established that, in conversion of nitrite to nitrate, one oxygen atom of nitrate arose from water and none from O2 or inorganic phosphate. This result confirms that of Kumar et al. [(1983) FEBS Lett. 152, 71-74]. Oxygen exchange between water and inorganic phosphate was small and that between water and nitrite or nitrate or any reaction intermediates between these two was not detected. Oxidation of nitrite was, therefore, effectively irreversible under the conditions employed. The uptake of extracellular phosphate was sufficient to allow significant transfer of 18O from phosphate to nitrate if oxidative phosphorylation had occurred by way of a P-O-N anhydride between phosphate (or ADP) and nitrate. The results are, therefore, inconsistent with the occurrence of a reaction of this type during nitrite oxidation.

Anhydrides↗

Oxidative phosphorylation in intact hepatocytes: quantitative characterization of the mechanisms of change in efficiency and cellular consequences.

Two mechanisms may affect the yield of the oxidative phosphorylation pathway in isolated mitochondria: (i) a decrease in the intrinsic coupling of the proton pumps (H+/2e- or H+/ATP), and (ii) an increase in the inner membrane conductance (proton or cation leak). Hence three kinds of modifications can occur and each of them have been characterized in isolated rat liver mitochondria (see preceding chapter by Rigoulet et al.). In intact isolated hepatocytes, these modifications are linked to specific patterns of bioenergetic parameters, i.e. respiratory flux, mitochondrial redox potential, DY, and phosphate potential. (1) The increase in H+/ATP stoichiometry of the mitochondrial ATP synthase, as induced by almitrine [20], leads to a decrease in mitochondrial and cytosolic ATP/ADP ratios without any change in the protonmotive force nor in the respiratory rate or redox potential. (2) In comparison to carbohydrate, octanoate metabolism by beta-oxidation increases the proportion of electrons supplied at the second coupling site of the respiratory chain. This mimics a redox slipping. Octanoate addition results in an increased respiratory rate and mitochondrial NADH/NAD ratio while protonmotive force and phosphate potential are almost unaffected. The respiratory rate increase is associated with a decrease in the overall apparent thermodynamic driving force (2deltaE'o - ndeltap) which confirms the 'redox-slipping-like' effect. (3) An increase in proton conductance as induced by the protonophoric uncoupler 2,4-dinitrophenol (DNP) leads to a decrease, as expected, in the mitochondrial NADH/NAD and ATP/ ADP ratios and in deltapsi while respiratory rate is increased. Thus, each kind of modification (proton leak, respiratory chain redox slipping or increase in H+/ATP stoichiometry of ATPase) is related to a specific set of bioenergetic parameters in intact cells. Moreover, these patterns are in good agreement with the data found in isolated mitochondria. From this work, we conclude that quantitative analysis of four bioenergetic parameters (respiration rate, mitochondrial NADH/ NAD ratio, protonmotive force and mitochondrial phosphate potential) gives adequate tools to investigate the mechanism by which some alterations may affect the yield of the oxidative phosphorylation pathway in intact cells.

2,4-Dinitrophenol↗

[The effect of hypoxia on oxidative phosphorylation and lipid peroxidation in rat liver mitochondria upon lung inflammation].

Hypoxic trainings of rats (maintenance in the test chamber at the "altitude" 4 km above the sea level for 7 hours a day for two weeks) prevent pneumonia-induced activation of peroxidation for lipids of the liver mitochondria. This increases the phosphorylating respiration rate when lipemic serum is used as an oxidation substrate (not succinate). In these experiments the efficiency of oxidative phosphorylation (delta ADP/delta O) when either succinate and glutamate or glutamate and malate have been oxidated corresponded to the values typical of intact animals and was higher when lipemic serum was used. It is supposed that rearrangement of energy reactions of mitochondria is connected with intensification of utilization of lipids and conjugation between their oxidation and phosphorylation. This rearrangement is apparently aimed to prevent the energy deficiency in the organism which arises in patients with pneumonia.

Animals↗

Demonstration and quantitation of catalytic and noncatalytic bound ATP in submitochondrial particles during oxidative phosphorylation.

Techniques are described for studying the labeling of ADP and ATP bound to the ATP synthase complex of beef heart submitochondrial particles catalyzing oxidative phosphorylation. These suffice for measurements of bound nucleotides during the time required for a single turnover, during steady state net ATP synthesis, or under quasiequilibrium conditions of ATP formation and hydrolysis. Results show that the "tightly bound" ATP associated with isolated submitochondrial particles does not become labeled by medium [32P]Pi rapidly enough to qualify as an intermediate in ATP synthesis. In contrast to chloroplast preparations, little or no bound [32P]Pi committed to ATP formation is present on particles during steady state synthesis. Also, highly active particles synthesizing ATP from [32P]Pi and filtered after EDTA addition have no detectable bound [32P]ATP even though several ATPs have been made per synthase complex. However, under quasiequilibrium conditions membrane-bound ADP and ATP are present whose labeling characteristics qualify them as intermediates in ATP synthesis. In addition, a hexokinase-accessibility approach shows the presence of a steady level of bound ATP. Lack of detection of bound intermediates under other conditions is regarded as reflecting the ready reversibility of oxidative phosphorylation, with consequent facile cleavage of bound ATP and release of bound Pi.

Adenosine Diphosphate↗

[The oxidative phosphorylation system of BHK-21 cells in suspension cultivation].

The state of the oxidative phosphorylation system in intact and digitonin-treated BHK-21 cells in the lag-, logarithmic and stationary growth phases has been studied. It is shown that during the growth of cell culture the rates of oxygen uptake and the extent of coupling of oxidation and phosphorylation change significantly.

Animals↗

The hydrophobic cationic cyanine dye inhibits oxidative phosphorylation by inhibiting ADP transport, not by electrophoretic transfer, into mitochondria.

The effect of the divalent cationic cyanine dye tri-S-C4(5) on oxidative phosphorylation in rat liver mitochondria was examined. The dye at about 100 n mols per mg mitochondrial protein inhibited state 3 respiration and ATP synthesis almost completely. However, it had no effect on submitochondrial particles, like other hydrophobic cations. The dye inhibited the transport of ADP into mitochondria mediated by the adenine nucleotide translocator. Thus, the inhibition of oxidative phosphorylation by the cationic dye was concluded to be due to its action on the adenine nucleotide translocator, not to its electrophoretic transfer into the inner space of mitochondria according to the inside-negative electrochemical potential.

Adenosine Diphosphate↗

[Activation of oxidative phosphorylation and energy-dependent absorption of Ca2+ and K+ ions by liver mitochondria of hibernating ground squirrels in hypotonic media].

Activation of initially suppressed oxidative phosphorylation and energy-dependent uptake of Ca2+ and K+ ions by liver mitochondria of hibernating gophers which is prevented by phospholipase A2 inhibitors, has been shown to occur in hypotonic media. Partial inhibition of the respiratory chain of liver mitochondria of active gophers by antimycin A which causes a decrease in the uncoupled respiration rate and delta psi down to values typical of mitochondria of hibernating gophers, practically exactly reproduced the suppression of oxidative phosphorylation and energy-dependent uptake of cations observed during hibernation. It was concluded that partial deenergization arising as a result of inhibition of the respiratory chain is the main and unique cause of suppression of energy-dependent functions of liver mitochondria of hibernating gophers.

Adenosine Triphosphate↗

Fatal neonatal liver failure and mitochondrial cytopathy (oxidative phosphorylation deficiency): a light and electron microscopic study of the liver.

Mitochondrial cytopathies are multisystemic disorders of extremely variable expression due to a deficiency in oxidative phosphorylation. Cases have recently been reported in which fatal liver failure with neonatal onset was the major clinical and biochemical syndrome. In this series we reviewed the liver histology of 10 such patients who died in the first weeks of life (from 3 days to 6 mo). In six cases the diagnosis was confirmed by study of the mitochondrial respiratory chain in the muscle, liver or both; in the other four, appropriate tests were not available for diagnosis but symptoms were identical and all other diagnoses were ruled out. In all 10 cases we noted significant steatosis, mostly microvesicular; widespread hepatocytic, canalicular and bile duct cholestasis with bile thrombi and cholangiolar proliferation; and different degrees of hepatosiderosis and glycogen depletion. Fibrosis took varying forms: perisinusoidal, periportal with the formation of septa, even precirrhosis. In the two cases of infants who died, one at 5 and one 6 mo, micronodular cirrhosis was also present. Mitochondria, either densely or loosely packed, were abnormal-pleiomorphic with few or no cristae and a granular fluffy matrix. Dense, large granules were seen in two cases. The association of neonatal liver failure and hyperlactacidemia should lead to immediate examination of the respiratory chain. The expression of this mitochondrial cytopathy can be lethal, associated with severe liver damage due to the deficiency in oxidative phosphorylation.

Female↗

Multi-omics reveals that burdock seed aglycone alleviates renal fibrosis by restoring mitochondrial oxidative phosphorylation function.

Renal fibrosis (RF), a common pathological process driving chronic kidney disease (CKD) progression to end-stage renal failure, is closely associated with oxidative phosphorylation (OXPHOS). Arctigenin (ATG), the main active component of burdock seed, exhibits anti-inflammatory and anti-fibrotic activities, but its mechanisms in RF treatment remain unclear. Here, we performed integrated transcriptomic and proteomic analyses to identify key targets and pathways of ATG in a unilateral ureteral obstruction-induced rat RF model. Multi-omics enrichment analysis revealed that NDUFS8 and NDUFS2 were the core targets of ATG, with the OXPHOS pathway as the central intersecting pathway. Our results suggest that ATG exerts anti-renal fibrosis effects by targeting the OXPHOS pathway to inhibit excessive reactive oxygen species production and oxidative stress. SIGNIFICANCE: Chronic kidney disease (CKD) continues to impose an escalating global health and socioeconomic burden, while renal fibrosis (RF), as the convergent pathological endpoint of virtually all progressive nephropathies, remains the principal determinant of irreversible renal failure and adverse clinical outcomes. Despite extensive efforts to develop antifibrotic therapies, effective clinical interventions remain elusive, largely due to the complex and multifactorial nature of RF pathogenesis. In this study, we employed an integrated multi-omics framework encompassing transcriptomics, proteomics, and metabolomics to systematically decipher the antifibrotic mechanism of arctigenin (ATG), a bioactive natural compound derived from traditional Chinese medicine. Our findings identify mitochondrial oxidative phosphorylation as the pivotal regulatory axis underlying the renoprotective effects of ATG and further establish key catalytic subunits of mitochondrial complex I as its direct molecular targets. Mechanistically, ATG not only restores complex I activity and reprograms mitochondrial energy metabolism but also preserves the intracellular stability and localization of these subunits, thereby preventing their aberrant release-mediated inflammatory activation and disrupting the self-perpetuating cycle linking metabolic dysfunction, inflammation, and fibrosis progression. Beyond revealing a previously unrecognized dual mechanism integrating metabolic and inflammatory regulation, this study provides compelling evidence that mitochondrial dysfunction is not merely a secondary consequence of tissue injury but a fundamental driver of fibrotic remodeling. Importantly, our work highlights the translational potential of natural product-based mitochondrial interventions for CKD treatment and supports a broader conceptual shift toward metabolism-centered therapeutic strategies for chronic fibrotic diseases. Given the central role of mitochondrial dysfunction across multiple organs, these findings may also have far-reaching implications for the treatment of systemic fibrosis-related disorders beyond the kidney.

Animals↗

Influence of rapid changes in cytosolic pH on oxidative phosphorylation in skeletal muscle: theoretical studies.

Cytosolic pH in skeletal muscle may vary significantly because of proton production/consumption by creatine kinase and/or proton production by anaerobic glycolysis. A computer model of oxidative phosphorylation in intact skeletal muscle developed previously was used to study the kinetic effect of these variations on the oxidative phosphorylation system. Two kinds of influence were analysed: (i) via the change in pH across the inner mitochondrial membrane and (ii) via the shift in the equilibrium of the creatine kinase-catalysed reaction. Our simulations suggest that cytosolic pH has essentially no impact on the steady-state fluxes and most metabolite concentrations. On the other hand, rapid acidification/alkalization of cytosol causes a transient decrease/increase in the respiration rate. Furthermore, changes in pH seem to affect significantly the kinetic properties of transition between resting state and active state. An increase in pH brought about by proton consumption by creatine kinase at the onset of exercise lengthens the transition time. At intensive exercise levels this pH increase could lead to loss of the stability of the system, if not compensated by glycolytic H+ production. Thus our theoretical results stress the importance of processes/mechanisms that buffer/compensate for changes in cytosolic proton concentration. In particular, we suggest that the second main role of anaerobic glycolysis, apart from additional ATP supply, may be maintaining the stability of the system at intensive exercise.

Adenosine Triphosphate↗

Uncoupling effect of protonophoric and nonprotonophoric analogs of carbonyl cyanide phenylhydrazone on mitochondrial oxidative phosphorylation.

Analogs of carbonyl cyanide phenylhydrazone providing no reaction with nucleophilic groups and lacking acidobasic properties, respectively, were synthesized for study of mechanism of uncoupling effect on oxidative phosphorylation. Their retention, influence on proton transport, abilities to SH--groups modify and to stimulate respiration in rat liver mitochondria, together with their physico-chemical properties, namely lipophilicity, acidobasicity and reactivity were characterized. The substitution of acidic hydrogen of the imino group resulted in the loss of both acidobasicity and uncoupling effect on oxidative phosphorylation. A decreased reactivity resulted from the substitutions of nitrile groups with the uncoupling activity remaining preserved.

Animals↗

[The influence of panthotenic acid mitochondrial oxidation and oxidative phosphorylation in liver of rats with alimentary obesity].

Alimentary obesity induced by the long-term feeding of rats by high-fat diet results the reducing of rate and efficiency of oxidative phosphorylation in liver mitochondria when NAD-dependent substrates are used. The treatment of the obese rats with panthotenic acid derivatives (phosphopantotenate, panthetin, panthenol) enhanced oxidative phosphorylation of pyruvate and fatty acid carnitine esters. Among investigated compounds panthenol activated respiratory control and phosphorylation rate more effectively. Moreover, panthenol, but not phosphopanthotenate nor panthetine, increased the activity of carnitine palmitoyltransferase 1 that confirms the preferable usage of fatty acids for mitochondrial oxidation under the influence of this compound.

Animals↗

Modulation of oxidative phosphorylation by Mg2+ in rat heart mitochondria.

The effect of varying the Mg2+ concentration on the 2-oxoglutarate dehydrogenase (2-OGDH) activity and the rate of oxidative phosphorylation of rat heart mitochondria was studied. The ionophore A23187 was used to modify the mitochondrial free Mg2+ concentration. Half-maximal stimulation (K0.5) of ATP synthesis by Mg2+ was obtained with 0.13 +/- 0.02 mM (n = 7) with succinate (+rotenone) and 0.48 +/- 0.13 mM (n = 6) with 2-oxoglutarate (2-OG) as substrates. Similar K0.5 values were found for NAD(P)H formation, generation of membrane potential, and state 4 respiration with 2-OG. In the presence of ADP, an increase in Pi concentration promoted a decrease in the K0.5 values of ATP synthesis, membrane potential formation and state 4 respiration for Mg2+ with 2-OG, but not with succinate. These results indicate that 2-OGDH is the main step of oxidative phosphorylation modulated by Mg2+ when 2-OG is the oxidizable substrate; with succinate, the ATP synthase is the Mg2+-sensitive step. Replacement of Pi by acetate, which promotes changes on intramitochondrial pH abolished Mg2+ activation of 2-OGDH. Thus, the modulation of the 2-OGDH activity by Mg2+ has an essential requirement for Pi (and ADP) in intact mitochondria which is not associated to variations in matrix pH.

Animals↗

Heart mitochondrial creatine kinase revisited: the outer mitochondrial membrane is not important for coupling of phosphocreatine production to oxidative phosphorylation.

The state of mitochondrial creatine kinase (CKmi-mi) in intact dog heart mitochondria and mitoplasts and the mechanism of its functional coupling with the oxidative phosphorylation system have been reinvestigated under different osmotic conditions and ionic compositions of the medium. It has been established that in a medium which mimics the cardiac cell cytoplasma, dissociation of CKmi-mi from the membrane of mitoplasts increases when the mitoplasts are swollen due to hypoosmotic treatment. It was shown by EPR that hypoosmotic treatment results in the enhancement of the mobility of phospholipids in the membrane bilayer. It has been also shown that when CKmi-mi is detached from the inner membrane in intact mitochondria in isotonic KCl solution, the effects of the coupling between CKmi-mi and oxidative phosphorylation via ATP/ADP translocase disappear in spite of the presence of CKmi-mi in the intermembrane space and intactness of the outer mitochondrial membrane. Therefore, this coupling cannot be explained by the "compartmented coupling" mechanism or "dynamic adenine nucleotide compartmentation" in the intermembrane space due to diffusion limitation for adenine nucleotides through the outer mitochondrial membrane, as has been supposed by several authors (F.N. Gellerich et al. (1987) Biochim. Biophys. Acta 890, 117-126; S.P.J. Brooks and C.H. Suelter (1987) Arch. Biochem. Biophys. 253, 122-132). The data obtained show that the displacement of the enzyme from the membrane results in significantly increased sensitivity of the coupled processes of aerobic phosphocreatine synthesis to inhibition by the product, phosphocreatine. Thus, all results show that under physiological osmotic and ionic conditions CKmi-mi remains firmly attached to the inner mitochondrial membrane and effectively coupled with ATP/ADP translocase due to intimate dynamic interaction between those proteins.

Animals↗

Chemotaxis away from uncouplers of oxidative phosphorylation in Bacillus subtilis.

In a capillary assay, uncouplers of oxidative phosphorylation and inhibitors of electron transport are repellents for Bacillus subtilis. They also cause transient tumbling in naturally smooth swimming strains. Tumbling strains can be made to swim smoothly by addition of attractant and then immediately returned to tumbling by subsequent addition of repellent. Arsenate does not cause transient tumbling, suggesting that decrease in concentration of adenosine triphosphate does not cause tumbling and that adenosine triphosphate concentration does not govern tumbling frequency. Instead, the evidence suggests that diminution of the energized state of the membrane, or membrane potential, causes tumbling although the level of the energized state itself does not govern tumbling frequency.

Adenosine Triphosphate↗

The oxygen dependence of mitochondrial oxidative phosphorylation measured by a new optical method for measuring oxygen concentration.

Oxygen-dependent quenching of phosphorescence has been used to measure the dependence of mitochondrial oxidative phosphorylation on oxygen concentration in suspensions of isolated rat liver mitochondria. An instrument has been designed which simultaneously monitors the phosphorescence lifetime of a fluorophor and the reduction of cytochrome c by dual wavelength spectrophotometry. The phosphorescence lifetime method gives very rapid (less than 100 ms) measure of the oxygen concentration (Vanderkooi, J. M., Maniara, G., Green, T. J., and Wilson, D. F. (1987) J. Biol. Chem. 262, 5476-5482) from concentrations characteristic of air-saturated media to as low as 2 x 10(-8) M. The results may be summarized as follows. For well coupled rat liver mitochondria at pH 7.0 and in the presence of ATP, as the oxygen concentration was lowered, increased cytochrome c reduction was observed to begin at oxygen concentrations greater than 20 microM. For mitochondria in the presence of uncoupler, cytochrome c reduction began at oxygen concentrations less than 1.0 microM. The oxygen dependence of reduction of cytochrome c in well coupled mitochondria treated with ATP was strongly dependent on the pH of the suspending medium. Reduction of cytochrome c began at higher oxygen concentrations as the pH was made more alkaline. The oxygen concentration for half-maximal respiratory rates was much larger for well coupled mitochondria treated with ATP (approximately 0.7 microM) than for mitochondria treated with uncoupler (less than 0.1 microM). It is concluded that the oxygen dependence of mitochondrial oxidative phosphorylation is such that mitochondria could function in their proposed role of tissue oxygen sensors for regulation of such diverse functions as local blood flow and electrical activity in the carotid body.

Adenosine Triphosphate↗

Diagnostic value of immunostaining in cultured skin fibroblasts from patients with oxidative phosphorylation defects.

In the last decades, a large variety of oxidative phosphorylation (OXPHOS) defects have been reported, expressed as an increasing variety of clinical phenotypes. With the expanding number of genes and proteins involved, new screening techniques leading to more effective diagnostic routes are in ever-increasing demand. Cultured skin fibroblasts from a cohort of patients with various OXPHOS defects, previously recognized by enzyme activity studies and blue native PAGE, were investigated with an immunocytochemical technique. Cytospins of cultured fibroblasts were air dried, fixed, and stained with antibodies specifically directed against subunits of each OXPHOS complex. Control cells stained homogeneously and strongly. In fibroblasts from five out of seven patients with a severe deficiency of one of the OXPHOS complexes, a homogeneous reduction of cytoimmunoreactivity of the affected complex was observed. In five out of seven fibroblast strains harboring a mitochondrial tRNA mutation, a mosaic pattern of staining was observed for both complexes I and IV, reflecting the heteroplasmic nature of the defect. The proportion of deficient fibroblasts varied considerably between cell strains from different subjects. The method described offers a convenient and rapid approach to first-line screening of OXPHOS defects. In association with routine assays of enzyme activity, the technique is helpful in orienting molecular investigation further.

Adolescent↗

Induction of GLUT1 mRNA in response to inhibition of oxidative phosphorylation.

In previous studies, we have shown that inhibition of oxidative phosphorylation in Clone 9 cells (a nontransformed rat liver cell line) by 5 mM azide results in a marked biphasic stimulation of glucose transport that is mediated by GLUT1 [M. Shetty, J. N. Loeb, and F. Ismail-Beige. Am.J. Physiol. 262 (Cell Physiol. 31): C527-C532, 1992]. The late phase of the response (at 8-24 h) is associated with a doubling of cell GLUT1 content and an 8- to 10-fold increment in GLUT1 mRNA abundance. To investigate the mechanisms mediating GLUT1 mRNA induction, we have examined the effect of incubation in the presence of azide on GLUT1 gene transcription. In nuclear run-on assays, the rate of GLUT1 gene transcription was increased 2.5 +/- 0.3-fold in nuclei from cells exposed to azide for 4 h. Additionally, GLUT1 mRNA turnover was decreased in cells treated with azide: upon inhibition of RNA synthesis by actinomycin D, GLUT1 mRNA content decreased with half-lives of 2.3 +/- 0.3 and 8.0 +/- 0.5 h in control cells and cells treated with azide for 4 h, respectively. GLUT1 mRNA half-life was most prolonged (> 12 h) when azide was added subsequent to the addition of actinomycin D, and the half-life continued to be prolonged (6.5 +/- 0.5 h) in cells exposed to azide for 16 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗