ATPase Activity Of Intact Mitochondria Research Articles

Effect of Graphene Oxide and Ammonia-modified Graphene Oxide Particles on ATPase Activity of Rat Liver Mitochondria

Graphene and its derivatives have become promising materials for biomedical applications in the last decade. Before their widespread application, however, evaluating their toxicity and mechanisms underlying interactions with cellular components is imperative. Aims: Assessment of the effect of two graphene derivatives, pristine graphene oxide (GO) and ammonia-modified GO (GO-NH2) particles, on the ATPase activity of rat liver mitochondria and ROS production. Methods: Liver mitochondria were isolated from male albino rats and treated with different concentrations of GO and GO-NH2 particles (4, 10, 25, and 50 μg/ml). ATPase activity of both, intact and uncoupled by freezing/thawing mitochondria was determined by the measurement of inorganic phosphate (Pi) released from ATP. The generation of hydrogen peroxide (H2O2) after exposure of mitochondria to GO and GO-NH2 particles was determined by a DCFH-D assay. Results: GO and GO-NH2 particles applied at concentrations of 4 and 50 μg/ml did not affect the ATPase activity of intact mitochondria. In contrast, in uncoupled mitochondria, they demonstrated a stimulating effect on ATPase activity. The impact of GO-NH2 was more substantial and concentration-dependent. ROS production was also higher in GO-NH2-treated mitochondria. Conclusion: The present study demonstrated that GO and GO-NH2 particles can exert a cytotoxic effect on mitochondria even after a short-time of exposure to both types of particles.

Photo-oxidase carbon dot-based nanozyme for breast cancer theranostics under normoxia condition

Ultra-small histidine-functionalized carbon nanodots (His C-dots) with engineered modality as photo-oxidative nanozymes for cancer theranostics were prepared by one step microwave-assisted pyrolysis. The role of chemically embedded imidazole ring into nanoparticle aromatic domains was to enhance the absorbance, fluorescence, and phosphorescence intensities in aqueous solution at room temperature. It contributed to the increase of pyrrolic nitrogen, which was responsible for the higher oxygen adsorption and better photosensitization under visible irradiation. The ability of nanozyme as theranostics was demonstrated on illuminated with visible light B16-F10 mouse melanoma cells with high metastatic potential under normoxic condition. The inhibition of cell migration was measured by wound healing assay after scratching confluent monolayer of the breast cancer cells. The microscopic data revealed that the metastatic migration could be controlled by the applied nanozyme dosage, which was responsible for the production of singlet oxygen and the causing of effective photo-induced cytotoxicity. The biocompatibility of the illuminated His C-dots was proved on ATPase activity of intact mitochondria and sub-mitochondrial particles, on diamine oxidase activity of liver and kidney fractions in dark mode, MTT assay as well as on non-illuminated adenocarcinomic human alveolar basal epithelial cells (A549) and human liver cancer cells (HepG2). The satisfactory ability of the reported nanoparticles as fluorescence anticancer agents makes them a promising platform for the development of oxidize-mimicking nanozymes with application in the photodynamic therapy.

Effects of a new antiprotozoal drug, N,N′-diphenyl-4-methoxy-benzamidine, on energy-linked functions of rat liver mitochondria

Amidines are chemically characterized by the presence of two nitrogen atoms that bind to the same carbon atom in its structure. Several biological activities have been ascribed to these compounds. Pentamidine, an aromatic diamidine, is effective in the treatment against Pneumocystis carinii and leishmaniasis, but it can also have severe side effects. New amidine derivatives have been synthesized, among them N,N′-diphenyl-4-methoxy-benzamidine (methoxyamidine), which is effective against Leishmania amazonensis (LD50 = 20 μM) and Trypanosoma cruzi (LD50 = 59 nM). In the present study, methoxyamidine toxicity was evaluated in isolated rat liver mitochondria at the same range of concentrations that exert antiprotozoal activity. In these organelles, actively oxidizing glutamate + malate inhibited state 3 respiration (25 nmol mg−1 of protein) by ∼15%. The sites of inhibition in the respiratory chain were complex I and the segment between ubiquinone and complex III. Methoxyamidine also stimulated state 4 respiration by ∼32% and ∼43% at 50 and 65 nmol mg−1 of protein, respectively. Its uncoupling effect was confirmed by a dose-dependent increase in oxygen consumption in state 4 respiration that was induced by oligomycin, reaching up to ∼69% (65 nmol mg−1 of protein) and an increase in ATPase activity in intact mitochondria by ∼27% and ∼83% at 50 and 65 nmol mg−1 protein, respectively. Swelling that was supported by the oxidation of glutamate + malate in the presence of sodium acetate was reduced by methoxyamidine by ∼16% and 32% at 50 and 65 nmol mg−1 protein, respectively. Mitochondrial swelling in the absence of substrate and in the presence of K+ and valinomycin was inhibited by ∼20% at the same concentrations, suggesting that methoxyamidine affects mitochondrial membrane permeability and fluidity. Our data show that methoxyamidine has slight effects on the energy-linked functions of isolated mitochondria at concentrations that correspond to the LD50 against Leishmania amazonensis and Trypanosoma cruzi. These findings may prompt further studies that evaluate methoxyamidine toxicity in vivo.

Influence of silver nanoparticles on the activity of rat liver mitochondrial ATPase

Mitochondria are one of the most sensitive targets for the toxicity of silver nanoparticles (AgNPs). Limited studies have demonstrated nanoparticle-induced impairment of mitochondrial oxidative phosphorylation. Reduced adenosine triphosphate (ATP) production can be due to inhibition of the respiratory chain and/or to direct effects of AgNPs on the activity of mitochondrial ATP synthase/ATPase. In this regard, we synthesized and evaluated the in vitro effects of two types of AgNPs with various environmental friendly coatings—polysaccharide starch (AgNPs/Starch, D av = 15.4 ± 3.9 nm) and trisaccharide raffinose (AgNPs/Raff, D av = 24.8 ± 6.8 nm), with an emphasis on their potential action on rat liver mitochondrial ATPase. Both types of AgNPs showed decoupling effect on intact mitochondria. Unlike AgNPs/Raff, AgNPs/Starch reduced 2,4-dinitrophenol-stimulated ATPase activity of intact mitochondria, which suggests that they are able to penetrate the inner mitochondrial membrane. Both types of AgNPs inhibited ATPase activity of freeze/thawed mitochondria and submitochondrial particles as the effects of AgNPs/Starch were more pronounced. UV–Visible absorption measurements showed changes in the absorption spectrum of AgNPs/Raff added to the reaction medium. This suggests nanoparticle aggregation and thus a possible reduction in their reactivity. The distinction in the effects of the two types AgNPs studied may be due to their different sizes and/or to the stabilizing agents used for their synthesis, which determine AgNPs colloidal stability in the assay media. This study suggests the need for further research into the importance of surface modifications of AgNPs for their interaction with cellular components. Our findings could contribute to the elucidation of the mechanisms underlying AgNPs toxicity.

Effect of enterococcin A 2000 on biological and synthetic phospholipid membranes

Lactic acid bacterium isolated from Bulgarian cheese and identified as Enterococcus faecium produces a small hydrophobic peptide substance (enterococcin A 2000) with broad spectrum of antimicrobial activity. The wide range of enterococcin antibacterial activity of this compound against Gram-positive, as well as against some Gram-negative bacteria, suggests a single mechanism of action. The mode of action of enterococcin A 2000 was studied in intact liver mitochondria and synthetic phospholipid liposomes used as model systems. Enterococcin A 2000 stimulated the ATPase activity in intact mitochondria. The kinetic curve of ATP hydrolysis differed from that obtained in presence of dinitrophenol (DNP) and showed a character similar to the ATP hydrolysis in the presence of classic ionophores. Enterococcin A 2000, when bound to synthetic phospholipid liposomes, permeabilized liposomes liberating the marker carboxyfluorescein (CF).

The uncoupling effect of the nonsteroidal anti-inflammatory drug nimesulide in liver mitochondria from adjuvant-induced arthritic rats.

The aim of the present study was to evaluate the changes caused by adjuvant-induced arthritis in liver mitochondria and to investigate the effects of the nonsteroidal anti-inflammatory drug nimesulide. The main alterations observed in liver mitochondria from arthritic rats were: higher rates of state IV and state III respiration with beta-hydroxybutyrate as substrate; reduced respiratory control ratio and impaired capacity for swelling dependent on beta-hydroxybutyrate oxidation. No alterations were found in the activities of NADH oxidase and ATPase. Nimesulide produced: (1) stimulation of state IV respiration; (2) decrease in the ADP/O ratio and in the respiratory control ratio; (3) stimulation of ATPase activity of intact mitochondria; (4) inhibition of swelling driven by the oxidation of beta-hydroxybutyrate; (5) induction of passive swelling due to NH(3)/NH(4)+ redistribution. The activity of NADH oxidase was insensitive to nimesulide. Mitochondria from arthritic rats showed higher sensitivity to nimesulide regarding respiratory activity. The results of this work allow us to conclude that adjuvant-induced arthritis leads to quantitative changes in some mitochondrial functions and in the sensitivity to nimesulide. Direct evidence that nimesulide acts as an uncoupler was also presented. Since nimesulide was active in liver mitochondria at therapeutic levels, the impairment of energy metabolism could lead to disturbances in the liver responses to inflammation, a fact that should be considered in therapeutic intervention.

Effects of the nonsteroidal anti-inflammatory drug piroxicam on rat liver mitochondria

1. 1. The effects of piroxicam, a nonsteroidal anti-inflammatory drug, on rat liver mitochondria were investigated in order to obtain direct evidence about a possible uncoupling effect, as suggested by a previous work with the perfused rat liver. 2. 2. Piroxicam increased respiration in the absence of exogenous ADP and decreased respiration in the presence of exogenous ADP, the ADP O ratios and the respiratory control ratios. 3. 3. The ATPase activity of intact mitochondria was increased by piroxicam. With 2,4-dinitrophenol uncoupled mitochondria, inhibition was observed. The ATPase activity of freeze-thawing disrupted mitochondria was insensitive to piroxicam. 4. 4. Swelling driven by the oxidation of several substrates and safranine uptake induced by succinate oxidation were inhibited. 5. 5. The results of this work represent a direct evidence that piroxicam acts as an uncoupler, thus, decreasing mitochondrial ATP generation.

Effect of methyl methacrylate on mitochondrial function and structure

1. 1. Treatment of isolated rat liver mitochondria with methyl methacrylate (MM) produced membrane disruption as evidenced by the release of citrate synthase, and changes in the ultrastructure of mitochondria. 2. 2. At concentration 0.1%, MM uncoupled oxidative phosphorylation as evidenced by stimulation of state 4 respiration supported either by pyruvate plus malate or succinate (+rotenone) and ATP-ase activity in intact mitochondria. 3. 3. At concentration 1% MM stimulated ATP-ase activity in intact mitochondria and succinate (+rotenone) oxidation at state 4 and was without effect on this substrate oxidation at state 3. 4. 4. MM inhibited pyruvate plus malate oxidation either at state 3 or in the presence of uncoupling agents. 5. 5. MM inhibited the NADH oxidase of electron transport particles at a concentration which failed to inhibit either succinic oxidase or the NADH-ferricyanide reductase activity. 6. 6. The data presented suggest that in the isolated mitochondria MM inhibits NADH oxidation in the vicinity of the rotenone sensitive site of complex I. 7. 7. The general conclusion is that MM may block an electron transport and to uncouple oxidative phosphorylation in rat liver mitochondria. The overall in vitro effect would be to prevent ATP synthesis which could result in cell death under in vivo conditions.

Duramycin effects on the structure and function of heart mitochondria: II. Energy conversion reactions

The polypeptide antibiotic duramycin has been reported to interact selectively with phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (Navarro et al., 1985, Biochemistry 24, 4645–4650). PE is a major component of mitochondrial membranes. Duramycin was used to probe the role of PE in mitochondrial energy conversion reactions with the following results: (i) Duramycin uncoupled mitochondrial respiration, decreasing the respiratory control ratio to 1 at 5 μ m. At concentrations of duramycin in excess of 10 μ m, ADP addition inhibited electron transport, (ii) Duramycin inhibited oxidative phosphorylation (C 50 < 2 μ m). (iii) Duramycin stimulated mitochondrial ATP hydrolysis modestly. The antibiotic was 7- to 16-fold less effective in this regard than concentrations of carbonylcyanide p-trifluoromethoxyphenylhydrazone (F-CCP) which produced comparable uncoupling, (iv) Duramycin inhibited uncoupled ATPase activity (C 50 = 8 μ m). Inhibition of the ATPase activity of intact mitochondria was blocked by 1 m m MgCl 2 and 5 m m CaCl 2; inhibition persisted in submitochondrial particles assayed in the presence of 3 m m MgCl 2. The effects on mitochondrial function of free fatty acids (FFA) and duramycin are similar in many respects. It is suggested that duramycin, like FFA, uncouples via a nonclassical mechanism, possibly by disrupting intramembrane H + transfer between redox and ATPase complexes. In addition, interaction of duramycin, either direct or indirect, with the F 0 moiety of the mitochondrial ATPase and with one or more components of the respiratory electron transport chain is proposed.

1284 MECHANISMS OF BILIRUBIN AND BILIVERDIN EFFECTS ON MEMBRANES

The effects of unconjugated bilirubin (UBR) and biliverdin (BV) on the physical state of phospholipid (PL) membranes were studied using black lipid membranes (BLM) and erythrocyte ghost membranes.At physiologic pH UBR produced green spots (precipitates) on BLM composed of asolectin (AS) and phosphatidyl serine (PS) at 4:1, and increased electric resistance at and below pH 7.4. Above pH 7.4 the electric resistance decreased. BV did not affect electric resistance.UBR delayed the formation of the bilayer structure of PL (AS: PS=4:1). When cholesterol was also in the membrane (4:1:2) the delay was even greater and this effect was seen at all pH levels.UBR inhibited (Na+,K+,Mg++)-ATPase activity of erythrocyte membranes; the degree of inhibition varied according to the reaction temperature, being greater at lower temperatures. UBR increased activation energies. The data suggests the induction of a change in the physical state of PL associated with membranes.UBR, BV and an artificial conjugated bilirubin (CBR) were evaluated for effects on mitochondrial ATPase activities. The association constant of CBR with bovine serum albumin was determined to be 1.2 × 105 M-1 (200 fold less than UBR). Preliminary data show a biphasic effect of UBR on Mg++-ATPase activity of intact mitochondria stimulating below and inhibiting above 250μM UBR. BV inhibits mitochondrial ATPase only when the membrane is destroyed indicating its inability to permeate the membrane (supported by NIH).

Effects of inhibitors of the respiratory chain and energy-transfer system on mitochondrial ATPase activity of houseflies

1. 1. The inhibition by three inhibitors of the respiratory chain (rotenone, antimycin A and cyanide), five inhibitors of energy-transfer reactions (oligomycin, dicyclohexylcarbodiimide, aurovertin, atractyloside and Dio-9) and two SH blocking agents (ethylmaleimide and mersalyl) of housefly mitochondria have been studied. 2. 2. The respiratory chain inhibitors weakly suppressed the ATPase activity induced by uncouplers and by Mg 2+ suggesting that alteration of the redox state of the respiratory chain had little effect on the ATPase activity. 3. 3. The uncoupler-stimulated ATPase was strongly inhibited by inhibitors of the energy-transfer reactions. The inhibition by oligomycin and dicyclohexylcarbodiimide was independent of ATP while that by Dio-9, atractyloside and aurovertin was ATP-dependent suggesting that the former inhibited in an irreversible while the latter in a reversible manner. The inhibition by oligomycin, atractyloside and aurovertin was also dependent on the concentration of DNP. High levels of DNP counteracted the inhibition. 4. 4. The Mg 2+-induced ATPase activity of intact mitochondria was suppressed by oligomycin but activated by aurovertin, Dio-9, ethylmaleimide and mersalyl. By contrast these agents inhibited the Mg 2+-ATPase in submitochondrial particles. Concentrations of atractyloside which selectively inhibited the uncoupler-stimulated ATPase were without effect on the Mg 2+-induced ATPase of intact mitochondria.

Interaction of a synthetic polyanion with rat liver mitochondria

The effect of a polyanion (a copolymer of methacrylate, malaete and styrene in a 1:2:3 proportion with an average molecular weight of 10 000) on respiration, ATPase activity and ADP/ATP exchange activity of rat liver mitochondria and submitochondrial particles has been studied. The polyanion (at 17–150 μg/ml concentration, 100 μg polyanion corresponding to 0.83 μequiv. of carboxylic groups) inhibits the oxidation of succinate and NAD-linked substrates in state 3 in a concentration-dependent manner. The extent of this inhibition can be decreased by elevating the concentration of ADP. State 4 respiration is not affected by the polyanion. It has also a slight inhibitory effect on the oxidation of the above mentioned substrates in the uncoupled state (a maximum inhibition of 37% at 166 μg/ml polyanion concentration), which is unaffected by ADP. The strong inhibition of state 3 respiration can be relieved by 2,4-dinitrophenol to the low level observed in the uncoupled state. Ascorbate+TMPD oxidation is slightly inhibited in state 3, while it is not inhibited at all in the uncoupled state. The polyanion, depending on its concentration, strongly inhibits also the DNP-activated ATPase activity of mitochondria (50% inhibition at 40 μg/ml polyanion concentration). The ATPase activity of sonic submitochondrial particles is also inhibited. However, this inhibition is incomplete (reaching a maximum of 65%) and higher concentrations of the polyanion are required than to inhibit the ATPase activity of intact mitochondria. The polyanion inhibits the ADP/ATP translocator activity of mitochondria, measured by the “back exchange” of [2- 3H]ADP. After a short preincubation of the mitochondria with the polyanion, the concentration dependence of the inhibition by the polyanion corresponds to that of the DNP-activated ATPase activity of intact mitochondria. It is concluded that, in intact mitochondria, the polyanion has at least a dual effect, i.e. it partially inhibits the respiratory chain between cytochrome b and cytochrome c, and strongly oxidative phosphorylation by blocking the ADP/ATP translocator.

Effects of ethacrynic acid and furosemide on phosphory-lation reactions of kidney mitochondria. Inhibition of the adenine nucleotide translocase

Previous reports that ethacrynic acid and furosemide diminish mitochondrial P : O ratios and reduce ( Na + + K +)-ATPase activity suggested that these diuretics may inhibit mitochondrial phosphorylation reactions. This possibility was initially studied by determining the effects of ethacrynic acid and furosemide on [ 32P]ATP exchange activity of rat kidney mitochondria. Concentrations of both drugs at 10 −4 M or greater, significantly inhibited [ 32P]ATP exchange. To investigate the mechanism of this inhibition, the effects of ethacrynic acid and furosemide on the ATPase activity of intact mitochondria and sonicated submitochondrial particles were determined. Both diuretics inhibited ATPase activity of intact mitochondria at 10 −4 M. In contrast, ATPase of submitochondrial particles was significantly less susceptible to inhibition by the diuretics. These results suggested that ethacrynic acid and furosemide inhibit adenine nucleotide transport across the mitochondrial membrane. This was directly tested by determining the effects of the diuretics on the mitochondrial adenine nucleotide translocase. At 5 · 10 −4 M, both ethacrynic acid and furosemide significantly inhibited adenine nucleotide transport. These findings suggest that ethacrynic acid and furosemide may diminish renal tubular solute reabsorption by direct inhibition of adenine nucleotide transport across the mitochondrial inner membrane.

The sites of action of indomethacin in rat liver mitochondria

Summary Effects of indomethacin on rat liver mitochondria were investigated in vitro . Indomethacin at concentrations of about 10 −4 M lowered ADP:O ratio and stimulated state 4 oxidation. At higher concentrations it inhibited state 4, state 3 and uncoupled oxidation with glutamate and succinate but not with ascorbate /+TMPD? as substrate. Indomethacin was also able to stimulate ATPase activity in intact mitochondria but not in the presence of 2,4-DNP. It is suggestedthat indomethacin acts as uncoupler of oxidative phosphorylation and as inhibitor of electron transport chain at the site above the cytochrome c in rat liver mitochondria. The mode of antipyretic action of indomethacin involving respiratory chain inhibition is discussed.

Effect of SH-reagents on the mitochondrial ATPase and induction of respiratory control in EDTA particle

AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL References 1 A. Fluharty, D.R. Sanadi, Proc. Natl. Acad. Sci., 46, (1960), 608– 616. U.S. 2 C. Cooper, A.L. Lehninger, J. Biol. Chem., 219, (1956), 519– 529. 3 P.D. Boyer, L.L. Bieber, R.A. Mitchell, G. Szabolcsi, J. Biol. Chem., 241, (1966), 5384– 5390. 4 C. Cooper, J. Biol. Chem., 235, (1960), 1815– 1819. 5 A. Fonyo, S. Bessman, Biochem. Biophys. Res. Commun., 24, (1966), 61– 66. 6 D.D. Tyler, Biochem. J., 107, (1968), 121– 123. 7 D.D. Tyler, Biochem. J., 107, (1968), 1968– 8 N. Haugaard, N.H. Lee, R. Kostrzewa, R.S. Horn, E.S. Haugaard, Biochim. Biophys. Acta, 172, (1969), 198– 204. 9 G.P. Brierley, M. Jurkowitz, K.M. Scott, Arch. Biochem. Biophys., 159, (1973), 742– 756. 10 J.H. Southard, J.T. Penniston, D.E. Green, J. Biol. Chem., 248, (1973), 3546– 3550. 11 T.P. Singer, E.B. Kearney, P. Bernath, J. Biol. Chem., 223, (1956), 599– 613. 12 M. Gutman, H. Mersmann, J. Luthy, T.P. Singer, Biochemistry, 9, (1970), 2678– 2687. 13 C.P. Lee, L. Ernster, Biochem. Biophys. Res. Commun., 18, (1956), 523– 529. 14 E. Racker, Fed. Proc., 26, (1967), 1335– 1340. 15 R.E. Beyer, D.L. Crankshaw, J.M. Kuner, Biochem. Biophys. Res. Commun., 28, (1967), 758– 763. 16 F.L. Crane, G.L. Glenn, D.E. Green, Biochim. Biophys. Acta, 22, (1956), 475– 487. 17 C.P. Lee, L. Ernster, Methods Enzymol., 10, (1967), 543– 548. 18 M.S. Selwyn, Biochem. J., 105, (1967), 279– 288. 19 V.K. Akimenko, I.B. Minkov, L.E. Bakeeva, A.D. Vinogradov, Biokhimiy, 37, (1972), 348– 359. 20 O.H. Lowry, S.A. Lopez, J. Biol. Chem., 162, (1946), 421– 428. 21 B. Chance, M. Nishimura, Methods Enzymol., 10, (1967), 641– 650. 22 A.G. Gornall, C.J. Bardawill, M.M. David, J. Biol. Chem., 177, (1949), 151– 166. 23 O.H. Lowry, N.J. Rosebrough, A.L. Farr, R.J. Randall, J. Biol. Chem., 193, (1951), 265– 24 C.H. McMurray, D.R. Trentham, Biochem. J., 115, (1969), 913– 921. 25 H.S. Penefsky, M.E. Pullman, A. Datta, E. Racker, J. Biol. Chem., 235, (1960), 3360– 26 C.P. Lee, L. Ernster, B. Chance, European J. Biochem., 8, (1969), 153– 163. 27 A.E. Senior, Biochemistry, 12, (1973), 3622– 3627. 28 S.T. Metelskii, I.A. Kozlov, Dokl. Akad. Nauk SSSR, 219, (1974), 1010– 1013. 29 Y. Kagawa, Biochim. Biophys. Acta, 265, (1972), 297– 338. 30 K.W. Lam, D. Swann, M. Elzinga, Arch. Biochem. Biophys., 130, (1969), 175– 182. 31 E. Racker, J.M. Fessenden-Raden, M.A. Kandrach, K.W. Lam, D.R. Sanadi, Biochem. Biophys. Res. Commun., 41, (1970), 1474– 1479. 32 B.P. Sani, D.R. Sanadi, Arch. Biochem. Biophys., 147, (1971), 351– 352. 33 S.W. Chamberlin, M. Gorman, A. Agtarap, Biochem. Biophys. Res. Commun., 34, (1969), 448– 453. 34 K.L. Carraway, R.B. Triplett, Biochim. Biophys. Acta, 200, (1970), 546– 566. Citing Literature Volume54, Issue2June 15, 1975Pages 230-233 ReferencesRelatedInformation

ATPase activity of kidney mitochondria stimulated by sodium

ATPase activity of intact mitochondria may be induced by the presence of sodium. Mitochondria obtained from kidney cortex or medulla demonstrate a higher sodium-stimulated ATPase than mitochondria prepared from liver. This difference is not due to a greater capacity of kidney mitochondria for ATP hydrolysis. Sodium-stimulated ATPase activity of mitochondria is not further enhanced by magnesium or potassium, nor is it inhibited by ouabain. Furthermore, the ATPase of submitochondrial particles is not enhanced by the presence of sodium. These results indicate that the ATPase activity of mitochondria which is stimulated by sodium is unrelated to the microsomal Na-K-ATPase. mitochondrial sodium-stimulated ATPase is affected by pH, anionic composition, furosemide, and ethacrynic acid. The demonstration that mitochondrial ATP hydrolysis can be activated by sodium suggests that intracellular sodium may directly influence intracellular energy metabolism.

Effects of respiratory chain inhibitors on mitochondrial ATPase activity

The effects of six respiratory chain inhibitors (amytal, rotenone, piericidin A, antimycin A, 2- N-heptyl-4-hydroxyquinoline N-oxide, and cyanide) on mitochondrial ATPase activity have been investigated. Each of these compounds inhibited the ATPase activity of intact mitochondria induced by uncoupling agents, ionophores, or alterations in ionic composition; the effects were variable depending upon the type and concentration of uncoupling agents or inhibitors utilized. The ATPase activity of sonicated submitochondrial particles was also diminished by respiratory inhibitors, but the isolated ATPase enzyme was not affected. We conclude from these results that these respiratory inhibitors interfere with the energy coupling mechanism of oxidative phosphorylation. The experimental observations tend to support the “chemical” theory, and appear to be less consistent with the “chemiosmotic” hypothesis of oxidative phosphorylation.

The effect of p,p′-DDT (Dicophane) and its metabolites on ATPase activity in rat liver mitochondria

The effect of DDT and its main metabolites on ATPase activity in rat liver mitochondria was studied. These compounds stimulated ATPase activity in intact mitochondria of rat liver and had no effect on ATPase activity in damaged mitochondria. This suggests that the uncoupling of the oxidative phosphorylation in mitochondria may be responsible for the toxic effect of DDT in mammals.

The Inhibitory Effect of 3-Nitropropionate on the Oxidative Phosphorylation in Rat Mitochondria

The effect of 3-nitropropionate (3-NPA)on oxidative phosphorylation by using mitochondria prepared from both rat liver and brain were investigated in connection with the toxicity of this material. It was found that 3-NPA inhibited oxidative phosphorylation. In this inhibition, the uptake of inorganic phosphate was blocked but the oxygen uptake was not influenced at all. Furthermore, increase in ATPase activity of intact mitochondria was shown by the addition of 3-NPA. Results showed that 3-NPA disturbed oxidative phosphorylation as an uncoupler. However, the degree of inhibition by 3-NPA was not so high in comparison with other well-known uncouplers.Thus the toxicity of 3-NPA is not due to the inhibition of oxidative phosphorylation. 3-NPA also does not affect on cytochrome oxidase activity.