Regulation of ion transport in mitochondria by respiratory chain enzymes and ATPase

The effects of the respiratory chain inhibitors as well as those of the inhibitors and substrates of ATP-synthetase in Ca2+ and K+ transport induced in the mitochondria upon the medium acidification in the presence of phosphate or arsenate, were investigated. Evidence has been obtained suggesting that under the experimental conditions used the transmembrane fluxes of K+ and Ca2+ are paralleled with H+ leakage through the proton channel of ATPase. It was found also that the system inducing cation fluxes at low pH values included peroxidation and hydrolysis of phospholipids. A scheme of regulation of ion transport in the mitochondria involving oxidative phosphorylation and oxidation and hydrolysis of lipids is proposed.     

Redox and specific effects of vanadium ions on respiratory enzymes

The effects of vanadium ions on the activities of enzymes of aerobic and anaerobic respiratory chains were investigated in vitro and in situ employing ¹H-, ¹⁴N-, ³¹P- and ⁵¹V- nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy and spectrophotometry. Vanadate and vanadyl ions produced either non-specific redox or specific activation or inhibition of respiratory enzymes. The oxidants molybdate and chromate and the reductant dithiothreitol were used to distinguish between non-specific and specific effects of vanadium ions on enzyme activities. The results suggested that components of anaerobic respiratory chains were more susceptible to vanadium ions than those of the aerobic respiratory chain     

Bioflavonoid effects on the mitochondrial respiratory electron transport chain and cytochrome c redox state

The polyphenolic structure common to flavonoids enables them to donate electrons and exert antioxidant activity. Since the mitochondrial electron transport chain consists of a series of redox intermediates, the effect of flavonoids in a complex mixture of polyphenols, as well as related pure flavonoids, was evaluated on the rat liver mitochondrial electron transport chain. A French maritime pine bark extract (PBE), a complex mixture of polyphenols and related pure flavonoids, was able to reduce cytochrome c reversibly, possibly by donation of electrons to the iron of the heme group; the donated electrons can be utilized by cytochrome c oxidase. Among single flavonoids tested, (-)-epicatechin gallate had the greatest ability to reduce cytochrome c. In addition, PBE competitively inhibited electron chain activity in both whole mitochondria and submitochondrial particles. A 3.5-fold increase in the apparent Km value for succinate was calculated from reciprocal plots. Among the flavonoids tested, taxifolin and (-)-epicatechin gallate showed minor inhibitory effects, while (+/-)-catechin and (+)-epicatechin were ineffective. Activities of NADH-ubiquinone, succinate-ubiquinone, and ubiquinol-cytochrome c reductases were inhibited by low concentrations of PBE to a similar extent. However, inhibition of cytochrome c oxidase activity required 4-fold higher PBE concentrations. These results suggest that flavonoids reduce cytochrome c and that PBE inhibits electron transport chain activity mainly through NADH-ubiquinone, succinate-ubiquinone, and ubiquinol-cytochrome c reductases.     

Bioflavonoid effects on the mitochondrial respiratory electron transport chain and cytochrome c redox state

Abstract

The polyphenolic structure common to flavonoids enables them to donate electrons and exert anti-oxidant activity. Since the mitochondrial electron transport chain consists of a series of redox inter-mediates, the effect of flavonoids in a complex mixture of polyphenols, as well as related pure flavonoids, was evaluated on the rat liver mitochondrial electron transport chain. A French maritime pine bark extract (PBE), a complex mixture of polyphenols and related pure flavonoids, was able to reduce cytochrome c reversibly, possibly by donation of electrons to the iron of the heme group; the donated electrons can be utilized by cytochrome c oxidase. Among single flavonoids tested, (-)-epicatechin gallate had the greatest ability to reduce cytochrome c. In addition, PBE competitively inhibited electron chain activity in both whole mitochondria and submitochondrial particles. A 3.5-fold increase in the apparent K_m value for succinate was calculated from reciprocal plots. Among the flavonoids tested, taxifolin and (-)-epicatechin gallate showed minor inhibitory effects, while (±)-catechin and (+)-epicatechin were ineffective. Activities of NADH-ubiquinone, succinate-ubiquinone, and ubiquinol-cytochrome c reductases were inhibited by low concentrations of PBE to a similar extent. However, inhibition of cytochrome c oxidase activity required 4-fold higher PBE concen-trations. These results suggest that flavonoids reduce cytochrome c and that PBE inhibits electron transport chain activity mainly through NADH-ubiquinone, succinate-ubiquinone, and ubiquinol-cytochrome c reductases.     

Synchronization of the function of respiratory chain enzymes and ATP-synthetase in energized mitochondria

The present study revealed that the previously described effect of ATP-synthetase inhibition concomitant with inhibition of the respiratory chain functioning could be observed under different absolute values of delta phi on the mitochondrial membrane. This points out that the membrane potential is not a unique regulator in the coupling of the ATP-synthetase and respiratory chain activities. At the same time, we succeeded in obtaining some evidence testifying that under conditions of ATP-synthetase inhibition the amount of functioning respiratory chains has to be proportional the functioning of the ATP-synthetases units. The osmolarity of the incubation medium was shown to control the state of the oxidative phosphorylation system. The respiratory chain and ATP-synthetase should be considered as an enzymatic supercomplex only when the osmolarity is close to 150-300 mOsm (within the physiological range). The coupling effectivity (ADP/O) of mitochondria under these conditions is maximal. It is concluded that the respiratory chain and ATP-synthetase are tightly bound from the kinetic point of view. The ATP-synthetase inhibition induces proportional inhibition of the respiratory chain enzymes and vice versa, the respiratory chain inhibition induces proportional inhibition of ATP-synthetase.     

Terminal branching of the respiratory electron transport chain in Neisseria meningitidis

The respiratory components of the envelope membrane preparation of Neisseria meningitidis were investigated. Oxidase activities were demonstrated in this fraction in the presence of succinic acid, reduced nicotinamide adenine dinucleotide, and ascorbate-N,N,N',N'-tetramethyl-p-phenylene-diamine (TMPD). Differences in the kinetics of inhibition by terminal oxidase inhibitors on the three oxidase activities indicated that ascorbate-TMPD oxidation involved only an azide-sensitive oxidase, whereas oxidation of the physiological substrates involved two oxidases, one of which was relatively azide resistant. Spectrophotometric studies revealed that ascorbate-TMPD donated its electrons exclusively to cytochrome o, whereas the physiological substrates were oxidized via both cytochromes o and a. The effects of class II inhibitors on the oxidases suggest terminal branching of the electron transport chain at the cytochrome b level. A model of the respiratory system in N. meningitidis is proposed.     

Mechanisms and functions of nonphosphorylating electron transport in respiratory chain of plant mitochondria

Data are raeviewed on mitochondrial systems whose functioning in plants diminishes the efficiency of oxidative phosphorylation. The involvement in this process of alternative oxidase, thermogenin-like uncoupling proteins, a 310 kD stress protein, free fatty acids, and the ADP/ATP antiporter is considered. The role of these systems is discussed with regard to thermogenesis, controlled production of reactive oxygen species, and regulation of bioenergetics and metabolism.     

Action of strong and weak nitrogenous bases on respiratory chain enzymes of mitochondria

The action of nitrogenous basis--electroneutral hydrazides (pK less than 7,50 and positive charged arylhydrazones (pK greater than 8)--on the respiratory chain enzymes and the influence of the electric charge and the size of alkoxylic group on biological activity compounds have been investigated. It has been shown that the size of alkoxylic group defines the selective action of nitrogenous basis on the enzymes of mitochondrial respiratory chain. The nitrogenous basis with a long alkoxylic group is shown to be inhibitors of NADH-dehydrogenase, their action is similar to rotenone. At the same time compounds with a short group are more effective in the inhibition of the enzymes of the initial segment in the respiratory chain mitochondria. The affinity of the organic cations of arylhydrazones to NADH-dehydrogenase is 100-1000 times higher than the affinity of electric neutral compounds.     

Modulation of TCA cycle enzymes and electron transport chain systems in experimental lung cancer

The modulatory effect of Withania somnifera along with paclitaxel on tricarboxylic acid (TCA) cycle key enzymes and electron transport chain complexes were investigated against lung cancer induced by benzo(a)pyrene in Swiss albino mice. Decreased activities of TCA cycle key enzymes such as isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and alpha-ketoglutarate dehydrogenase (alpha-KGDH) in lung cancer bearing animals were observed. Upon W. somnifera along with paclitaxel administration the above biochemical changes were inclined towards normal control animal values. Activities of mitochondrial enzymes and electron transport complexes were analyzed in the experimental groups to determine the efficiency of energy production. This study further confirms the chemotherapeutic effect of W. somnifera along with paclitaxel which is found to be more effective in the treatment of lung cancer. Thus these results are consistent with our hypothesis that the combination chemotherapy of W. somnifera along with paclitaxel as a promising chemotherapeutic agent.     

Effect of low temperature on electron transport in plant mitochondria respiratory chain

The etiolated 2.5-day winter wheat sprouts were chilled at 3 degrees C during 24 to 144 hours. After 24 h cooling, shoot intact mitochondria showed a high degree of activation of the alternative oxidase, which was measured as sodium azide and benzohydroxamate sensitivity of the organelles respiration with succinate as a substrate. The role of the alternative oxidase in limiting the level of reactive oxygen species produced in the stressed plant tissues is discussed.     

Redox regulation of intercellular transport

Plant cells communicate with each other via plasmodesmata (PDs) in order to orchestrate specific responses to environmental and developmental cues. At the same time, environmental signals regulate this communication by promoting changes in PD structure that modify symplastic permeability and, in extreme cases, isolate damaged cells. Reactive oxygen species (ROS) are key messengers in plant responses to a range of biotic and abiotic stresses. They are also generated during normal metabolism, and mediate signaling pathways that modulate plant growth and developmental transitions. Recent research has suggested the participation of ROS in the regulation of PD transport. The study of several developmental and stress-induced processes revealed a co-regulation of ROS and callose (a cell wall polymer that regulates molecular flux through PDs). The identification of Arabidopsis mutants simultaneously affected in cell redox homeostasis and PD transport, and the histological detection of hydrogen peroxide and peroxidases in the PDs of the tomato vascular cambium provide new information in support of this novel regulatory mechanism. Here, we describe the evidence that supports a role for ROS in the regulation of callose deposition and/or in the formation of secondary PD, and discuss the potential importance of this mechanism during plant growth or defense against environmental stresses.     

Alternative respiratory oxidases to study the animal electron transport chain

Oxidative phosphorylation is a common process to most organisms in which the main function is to generate an electrochemical gradient across the inner mitochondrial membrane (IMM) and to make energy available to the cell. However, plants, many fungi and some animals maintain non-energy conserving oxidases which serve as a bypass to coupled respiration. Namely, the alternative NADH:ubiquinone oxidoreductase NDI1, present in the complex I (CI)-lacking Saccharomyces cerevisiae, and the alternative oxidase, ubiquinol:oxygen oxidoreductase AOX, present in many organisms across different kingdoms. In the last few years, these alternative oxidases have been used to dissect previously indivisible processes in bioenergetics and have helped to discover, understand, and corroborate important processes in mitochondria. Here, we review how the use of alternative oxidases have contributed to the knowledge in CI stability, bioenergetics, redox biology, and the implications of their use in current and future research.