Energy-linked Reactions In Mitochondria Research Articles

Aberrant energy-linked reactions in mitochondria isolated from the livers of sheep infected with the liver fluke Fasciola hepatica

Respiration by mitochondria isolated from the livers of sheep following infection up to 15 weeks with F. hepatica was measured with the respiratory substrates pyruvate (plus malate) and succinate in the absence and presence of ADP; the rates were compared with those obtained by mitochondria isolated from livers of uninfected sheep. It was found that respiration supported by both substrates in mitochondria isolated from the left lobe but not the middle lobe of 4-week infected sheep exhibited abnormalities such that the acceptor control ratios were only marginally above one. Some, but not total, recovery was seen in the later stages of infection. The aberrant respiratory behaviour is similar to that observed with infected rats.

Aberrant energy-linked reactions in mitochondria isolated from the livers of rats infected with the liver fluke Fasciola hepatica

The respiratory properties of mitochondria isolated from the livers of rats infected with the parasite Fasciola hepatica were examined. Oligomycin-sensitive ATPase activity was also examined during the acute stage (2-4 weeks post-infection). At 2,4 and 6 weeks post-infection, mitochondrial respiration in vitro (supported by site I and site II substrates) was completely uncoupled. Limited respiratory control had returned by 11 weeks post-infection, but complete recovery was not observed even at 21 weeks post-infection. At 4 weeks post-infection, uncoupled respiration (from all three energy-conserving sites) was also markedly attenuated (to the greatest extent with NADH-linked substrate). Except for pyruvate-supported respiration, this attenuation was not apparent at any other stage of the infection. The attenuation of pyruvate-supported respiration declined, but was still present, at 6 weeks post-infection. In addition to these perturbations in mitochondrial respiratory properties, mitochondrial ATPase activity at 4 weeks post-infection was insensitive to oligomycin, indicating a change in the structural integrity of the ATPase complex.

Inhibition of energy metabolism by benzoxazolin-2-one

1. 1. The effects of the title compound (BOA) on energy-linked reactions in mitochondria were studied. 2. 2. BOA inhibited electron transfer between the flavin and ubiquinone in Complex I, and ATP synthesis at the F 1 moiety of the ATPase complex. 3. 3. These results are discussed in relation to the toxicity of BOA towards a wide range of aerobic organisms.

Effects of tricyclic antidepressant drugs on energy-linked reactions in mitochondria

The effects of impramine and chlorimipramine on energy-linked reactions in mitochondria were characterized. Both compounds exhibited some characteristics of classical uncouplers of oxidative phosphorylation, i.e. they released respiratory control, hindered ATP synthesis, and enhanced ATPase activity of isolated rat liver mitochondria. Unlike classical uncouplers, however, these compounds only weakly stimulated proton uptake in intact mitochondria. They also exhibited unusual effects on energy-linked reactions in beef heart submitochondrial particles (SMP). Both compounds inhibited NADH oxidation in SMP in an “oligomycin-like” manner, and inhibited ATPase activity of SMP and the soluble F 1-ATPase. In contrast, the drugs weakly inhibited ATPase activities of bovine adrenal gland chromaffin granules and resealed granule ghosts. The mechanisms responsible for the multiple effects on mitochondrial energy-linked processes are unclear. They may be related to the hydrophobicity of the drugs, as has been shown for other hydrophobic amines.

Energy-linked reactions in mitochondria: The effects of some inhibitors and their use in the location of the transhydrogenase enzyme

The effects of 2-phenylisatogen, 2-phenylindolone, N-ethylmaleimide and p-hydroxymercuribenzoate on transhydrogenase reactions are compared. 2-Phenylindolone and N-ethylmaleimide inhibited the energy-linked transhydrogenase at lower concentrations than they inhibited the non-energy-linked transhydrogenase, whereas the reactions were equally sensitive to p-hydroxymercuribenzoate. 2-Phenylisatogen inhibited the transhydrogenase reactions when added to the mitochondria prior to sonication, but not when added directly to the assay medium. The results are discussed in terms of the location of the transhydrogenase enzyme.

Inhibition by calcium of adenine nucleotide translocation in mitochondria isolated from ehrlich ascites tumour cells

A carrier-system specifically involved in transporting AdN has been shown to exist in mitochondria isolated from a variety of eukaryotic cells. This translocase which is inhibited by atractyloside is located in the inner membrane of these organelles and operates by catalyzing an exchange of endogenous with exogenous AdN; generally ADP is exchanged at a rate greater than that of ATP (for review see ref. [I] ). It has become clear from recent work carried out, particularly in our laboratory [ 2-61 that low concentrations of Ca’+ stimulate the translocation of AdN in rat liver and heart mitochondria. We have proposed a mechanism for this which involves interaction of the Ca2+ with phospholipid located in the membrane environment of the AdN translocator. The stimulation is greater for ATP than for ADP and is not identifiable with that (of ATP) induced by uncouplers of oxidative phosphorylation [2, 31. While investigating the effects of Ca2 + on energylinked reactions in mitochondria from Ehrlich ascites tumour cells [7-lo] we observed that quite low levels of this ion prevented the usual respiratory response to ADP, a property not seen in normal mitochondria. It occurred to us that this inhibitory action might be related in some way to an interaction of the Ca2+ with the AdN translocase system [9, lo].

Energy-linked reactions in mitochondria: A requirement for ubiquinone after pentane extraction

Energy-linked reactions in mitochondria: A requirement for ubiquinone after pentane extraction

Inhibition of SH-enzymes by ethacrynic acid

Enzymes with essential SH-groups (succinate dehydrogenase, proline oxidase, glycerinaldehyde-3-phosphate dehydrogenase) are inhibited by ethacrynic acid. The concentrations needed are comparable with those known to inhibit energy-linked reactions in mitochondria. It is suggested that the action of ethycrynic acid is not only due to its influence on mitochondrial energy conserving reactions.

Energy-linked reactions in mitochondria. Studies on the reduction of NAD+ by succinate.

Summary 1. The ATP-dependent reduction of NAD + by succinate catalysed by submitochondrial particles prepared from beef, sheep and pig heart mitochondria has been examined 2. The general features of the reaction are similar to those described by other workers, especially the sensitivity of the reaction to inhibitors and uncouplers of respiration and oxidative phosphorylation such as 2,4-dinitrophenol, Amytal, rote-none and oligomycin 3. The stereospecificity of hydrogen transfer in the ATP-dependent reduction of NAD + has been investigated using [ 3 H]N AD + as the hydrogen acceptor and methods are described for the preparation and separation of tritiated pyridine nucleotides 4. Stereospecificity studies show that the terminal reductive step in the energy-linked reduction of NAD + by succinate is catalysed by an enzyme of B-specificity, possibly the NADH dehydrogenase (EC 1.6.99.3) flavoprotein system. These results also exclude malate dehydrogenase (EC 1.1.1.37), an enzyme of A-specificity, as a participant in the reaction.

Energy-linked reactions in mitochondria: studies on the mechanism of the energy-linked transhydrogenase reaction.

Summary 1. The mechanism of both the energy-linked and non-energy-linked trans-hydrogenase reaction catalysed by submitochondrial particles from beef-heart mitochondria has been examined using 3 H- and 14 C-labelled pyridine nucleotides as substrates. 2. The energy-linked transhydrogenase reaction does not proceed via a net group transfer of either the adenine or nicotinamide moieties or of phosphate from one pyridine nucleotide to another. 3. Studies with 3 H-labelled pyridine nucleotides show conclusively that in the energy-linked transhydrogenase reaction hydrogen is transferred directly from the A locus of NADH to the B locus of NADP + , i.e . the energy-linked transhydrogenase is an A:B transhydrogenase involving direct hydrogen transfer. 4. Studies on the non-energy-linked transhydrogenase show conclusively that the stereochemistry of the non-energy-linked reaction is identical to that of the energy-linked transhydrogenase reaction. 5. When the reaction is carried out in tritiated water there is only a low incorporation of tritium into NADPH thus confirming that the reaction is one involving direct hydrogen transfer.

Energy-linked reactions in mitochondria: Manometric errors in the determination of P/O ratios

Energy-linked reactions in mitochondria: Manometric errors in the determination of P/O ratios