bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity of Ca2+ Transport of Mitochondria to Reactive Oxygen Species
Authors: Yang Zhi-wei , Yang Fu-yu
Published: November 2003

The relationship between Ca2+ transport and energy transduction of myocardial mitochondria in the presence of reactive oxygen species was investigated. Following treatment with oxygen free radicals [superoxide(O2•) or hydroxyl radical (•)OH], lipid free radicals in myocardial mitochondrial membrane could be detected by using the method of EPR spin trap. Simultaneously there were obvious alterations in the free Ca2+ ([Ca2+]m) in the mitochondrial matrix; the physical state of membrane lipid; the efficiency of oxidative phosphorylation (ADP/O); the value of the respiratory control ratio (RCR); and the membrane potential of the inner membrane of myocardial mitochondria. If the concentrations of reactive oxygen species were reduced by about 30%, the alterations in the physical state of the membrane lipid and energy transduction of myocardial mitochondria were not observed, but the changes in Ca2+ homeostasis remained. We conclude that Ca2+ transport by myocardial mitochondria is more sensitive to agents such as (O2•) or •OH, etc. than are oxidation phosphorylation and the respiratory chain.
Oxidative Damage and Fragmentation of Mitochondrial DNA in Cellular Apoptosis
Authors: Ozawa Takayuki
Published: November 2003

The molecular genetics and bioenergetics of oxidative damage, fragmentation, and fragility of mitochondrial DNA in cellular apoptosis is reviewed in connection with the “redox mechanism of ageing”.
The Physiological Significance of Mitochondrial Proton Leak in Animal Cells and Tissues
Authors: Rolfe David F. S. , Brand Martin D.
Published: November 2003

Mitochondrial proton leak is an important component of cellular metabolism in animals and may account for as much as one quarter to one third of the Standard Metabolic Rate of the rat. The activity of the proton leak pathway is different in a wide range of animal species and in different thyroid states. Such differences imply some function for proton leak and candidates for this function include thermogenesis, protection against reactive oxygen species, endowment of metabolic sensitivity and maintenance of carbon fluxes.
Generating, Partitioning, Targeting and Functioning of Superoxide in Mitochondria
Authors: Liu Shu-sen
Published: November 2003

Recently, we proposed a hypothetical model of coexistence of “Reactive oxygen cycle” with Q cycle and H+ cycle in mitochondrial respiratory chain to combine both processes of univalent electron leak for production of superoxide and of proton leak across inner mitochondrial membrane. This review presents a more detailed description of this model and summarizes the supporting experimental evidence obtained.
Genes of Human ATP Synthase: Their Roles in Physiology and Aging
Authors: Kagawa Yasuo , Hamamoto Toshiro , Endo Hitoshi , Ichida Masaru , Shibui Hirobumi , Hayakawa Morisada
Published: November 2003

The reaction of ATP synthase (F0F1) is the final step in oxidative phosphorylation (OXPHOS). Although OXPHOS has been studied extensively in bacteria, no tissue-specific functions nor bioenergetic disease, such as mitochondrial encephalomyopathy and aging occur in these organisms. Recent developments of the Human Genome Project will become an important factor in the study of mammalian bioenergetics. To elucidate the physiological roles of human F0F1, genes encoding the subunits of F0F1 were sequenced, and their expression in human cells was analyzed. The following results were obtained: A. The roles of the residues in F0F1 are not only to transform the energy of the electrochemical potential (ΔμH+) across the membrane, but also to respond rapidly to the changes in the energy demand by regulating the intramolecular rotation of F0F1 with the ΔμH+ and the inhibitors of the ATPase. B. The roles of the control regions of the F0F1 genes, are to coordinate both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) depending on the energy demand of the cells, especially in muscle. C. The cause of the age-dependent decline of ATP synthesis has been attributed to the accumulation of mutations in mtDNA. However, the involvement of nDNA in the decline is also important because of telomere shortening in somatic cells, and age-dependent mtDNA expression analyzed with ρ° cells (cells without mtDNA).
A Possible Role of Slips in Cytochrome C Oxidase in the Antioxygen Defense System of the Cell
Authors: Papa S. , Guerrieri F. , Capitanio N.
Published: November 2003

Evidence is available showing that the coupling efficiency of the proton pump in cytochrome c oxidase of mitochondria can under certain conditions decrease significantly below the maximum attainable value. The view is developed that slips in the proton pump of cytochrome c oxidase represent an intrinsic switch mechanism which regulates the relative contribution of energy transfer and respiratory protection against oxygen toxicity by the oxidase.
Mitochondrial Oxygen Radical Formation during Reductive and Oxidative Stress to Intact Hepatocytes
Authors: Lemasters John J. , Nieminen Anna-Liisa
Published: November 2003

After simple respiratory inhibition, glycolytic substrates prevent cell death by providing an alternate source of cellular ATP. When mitochondrial uncoupling ensues, the uncoupler-stimulated mitochondrial ATPase hydrolyzes ATP formed by glycolysis and protection is lost. Electron transfer components abnormally reduced by respiratory inhibition, especially ubisemiquinone, react directly with oxygen to form toxic radicals. Mitochondria also generate reactive oxygen species after exposure to oxidant chemicals. A consequence is onset of the mitochondrial permeability transition, which leads to uncoupling, cellular ATP depletion and loss of viability. Thus, mitochondria are both a source and a target of toxic oxygen radicals in cell injury.
Significance of the β-Subunit in the Biogenesis of Na+/K+-ATPase
Authors: Ueno Susumu , Takeda Kazuo , Noguchi Shunsuke , Kawamura Masaru
Published: November 2003

This review summarizes our experiments on the significance of the β-subunit in the functional expression of Na+/K+-ATPase. The β-subunit acts like a receptor for the α-subunit in the biogenesis of Na+/K+-ATPase and facilitates the correct folding of the α-subunit in the membrane. The α-subunit synthesized in the absence of the β-subunit is subjected to rapid degradation in the endoplasmic reticulum. Several assembly sites are assigned in the sequence of the β-subunit from the cytoplasmic NH2-terminal domain to the extracellular COOH-terminus: the NH2-terminal region of the extracellular domain, the conservative proline in the third disulfide loop, the hydrophobic amino acid residues near the COOH-terminus and the cysteine residues forming the second and the third disulfide bridges. Upon assembly, the β-subunit confers a resistance to trypsin on the α-subunit. The conformations induced in the α-subunit of Na+/K+-ATPase by Na+/K+- and H+/K+-ATPase β-subunits are somehow different from each other and are named the NK-type and KH-type, respectively. The extracellular domain of the β-subunit is involved in the folding of the α-subunit leading to trypsin-resistant conformations. The sequences from Cys150 to the COOH-terminus of the Na+/K+-ATPase β-subunit and from Ile89 to the COOH–terminus of the H+/K+-ATPase β-subunit are necessary to form trypsin-resistant conformations of the NK- and HK-type. respectively. The first disulfide loop of the extracellular domain of the β-subunits is critical in the expression of functional Na+/K+-ATPase.
The Role of Reactive Oxygen Species in Mitochondrial Permeability Transition
Authors: Vercesi Anibal E. , Kowaltowski Alicia J. , Grijalba Mercedes T. , Meinicke André R. , Castilho Roger F.
Published: November 2003

We have provided evidence that mitochondrial membrane permeability transition induced by inorganic phosphate, uncouplers or prooxidants such as t-butyl hydroperoxide and diamide is caused by a Ca2+-stimulated production of reactive oxygen species (ROS) by the respiratory chain, at the level of the coenzyme Q. The ROS attack to membrane protein thiols produces cross-linkage reactions, that may open membrane pores upon Ca2+ binding. Studies with submitochondrial particles have demonstrated that the binding of Ca2+ to these particles (possibly to cardiolipin) induces lipid lateral phase separation detected by electron paramagnetic resonance experiments exploying stearic acids spin labels. This condition leads to a disorganization of respiratory chain components, favoring ROS production and consequent protein and lipid oxidation.
Respiratory Protection of Nitrogenase Activity in Azotobacter vinelandii—Roles of the Terminal Oxidases
Authors: Poole Robert K. , Hill Susan
Published: November 2003

Nitrogen fixation by aerobic prokaryotes appears paradoxical: the nitrogen-fixing enzymes—nitrogenases—are notoriously oxygen-labile, yet many bacteria fix nitrogen aerobically. This review summarises the evidence that cytochrome bd, a terminal oxidase unrelated to the mitochondrial and many other bacterial oxidases, plays a crucial role in aerotolerant nitrogen fixation in Azotobacter vinelandii and other bacteria by rapidly consuming oxygen during uncoupled respiration. We review the pertinent properties of this oxidase, particularly its complement of redox centres, the catalytic cycle of oxygen reduction, the affinity of the oxidase for oxygen, and the regulation of cytochrome bd gene expression. The roles of other oxidases and other mechanisms for limiting damage to nitrogenase are assessed.
Characterisation of the Role of Calcium in AlF4-Induced Long-Term Potentiation in Area CA1 of Rat Hippocampus
Authors: Breakwell N. A. , Publicover S. J.
Published: November 2003

We investigated calcium influx in the long lasting potentiation induced in area CA1 of rat hippocampus by brief bath application of the G-protein activator AlF4−(NaF/AlCl3). Brief (10 min) bath application of AlF4− in standard saline (with 2mM Ca2+) consistently induced a long lasting potentiation which was not observed if AlF4− was bath-applied in nominally calcium free saline. Increasing the potential calcium influx, either by raising extracellular calcium concentration to 3.5 mM or by addition of the voltage operated calcium channel (VOCC) agonist BayK8644. failed to increase the number of slices exhibiting potentiation or the mean level of potentiation. Bath application of AlF4− in the presence of the VOCC antagonist failed to block the potentiation and AlF4− readily induced a long lasting potentiation under voltage clamp conditions, strongly suggesting that the calcium influx required for AlF4-induced potentiation is not through NMDA receptors or VOCC channels. It is suggested that the calcium required may be provided by an ongoing recharging and emptying of IP3 sensitive intracellular Ca2+ stores.
Role of the Mitochondrial Permeability Transition Pore in Apoptosis
Authors: Hirsch Tamara , Marzo Isabel , Kroemer Guido
Published: November 2003

Mitochondrial permeability transition (PT) involves the formation of proteaceous, regulated pores, probably by apposition of inner and outer mitochondrial membrane proteins which cooperate to form the mitochondrial megachannel (=mitochondrial PT pore). PT has important metabolic consequences, namely the collapse of the mitochondrial transmembrane potential, uncoupling of the respiratory chain, hyperproduction of superoxide anions, disruption of mitochondrial biogenesis, outflow of matrix calcium and glutathione, and release of soluble intermembrane proteins. Recent evidence suggests that PT is a critical, rate limiting event of apoptosis (programmed cell death): (i) induction of PT suffices to cause apoptosis; (ii) one of the immediate consequences of PT, disruption of the mitochondrial transmembrane potential (ΔΨm), is a constant feature of early apoptosis; (iii) prevention of PT impedes the ΔΨm collapse as well as all other features of apoptosis at the levels of the cytoplasma, the nucleus, and the plasma membrane; (iv) PT is modulated by members of the apoptosis-regulatory bcl-2 gene family. Recent data suggest that the acquisition of the apoptotic phenotype, including characteristic changes in nuclear morphology and biochemistry (chromatin condensation and DNA fragmentation), depends on the action of apoptogenic proteins released from the mitochondrial intermembrane space.
How Do Bacteria Avoid High Oxygen Concentrations?
Authors: Zhulin Igor B. , Johnson Mark S. , Taylor Barry L.
Published: November 2003

Bacteria, such as Escherichia coli and Azospirillum brasilense, avoid microenvironments with elevated oxygen concentrations, not by sensing reactive oxygen derivatives, but by sensing a metabolic down-shift that results from elevated oxygen levels. A novel protein, Aer, and the chemotaxis serine receptor, Tsr, have recently been identified as transducers for aerotaxis which monitor internal energy levels in the bacteria.
Vitamin E Decreases the Order of the Phospholipid Model Membranes in the Gel Phase: An FTIR Study
Authors: Severcan Feride
Published: November 2003

The effect of α-tocopherol on the frequency of the CH2 stretching bands of infrared spectra of dipalmitoylphosphotidylcholine multibilayers has been investigated, both in H2O and 2H2O buffer, to determine the reason for the discrepancy in the literature between the results of different spectroscopic techniques relating to the effect of α-tocopherol on membrane order in the gel phase. In contrast to previous FTIR studies, the present FTIR results indicate that αT increases the frequencies of the CH2 stretching bands in the gel phase, which implies an increase in the number of gauche conformers (increase in disordering), which is in agreement with other ESR and NMR spectroscopic studies.
Cu,Zn-Superoxide Dismutase Gene Dosage and Cell Resistance to Oxidative Stress: A Review
Authors: Peskin Alexander V.
Published: November 2003

It is well established that superoxide dismutase (SOD) is the irresplaceable enzyme for aerobic lifestyle. Our understanding of its role has made strides recently as the result of gene transfection approach. Available data on consequences of Cu,Zn-SOD gene transfection in cell resistance to oxygen toxicity are reviewed. There are data that increasing only Cu,Zn-SOD can be toxic, and the balance between Cu,Zn-SOD and peroxide-removing enzymes is supposed to be of prime importance in the antioxidant defence. Role of Cu,Zn-SOD deregulation in carcinogenesis is discussed.
Membrane-Linked Systems Preventing Superoxide Formation
Authors: Skulachev Vladimir P.
Published: November 2003

New facts and ideas concerning the membrane-linked mechanisms preventing superoxide formation are summarised here. It is assumed that aerobic cells possess several lines of anti-ROS defence, including optimisation of the intracellular oxygen concentration, decrease in the concentration and life-time of one-electron O2 reductants such as CoQH; and mitochondrial and cell selections, i.e. elimination of mitochondria and cells producing ROS at high rate. It is postulated that ROS-dependent pore opening and ROS-dependent apoptosis are involved in mitochondrial and cell selections.
D-Glucose but Not Insulin Reduces N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-Induced Shape Changes in Suspended Human Neutrophils
Authors: Oldenborg Per-Arne , Sehlin Janove
Published: November 2003

The effects of glucose (5–25 mM) and insulin concentration (40–320 μU/ml) on the cell shape of neutrophil granulocytes from healthy humans were studied. Both non-activated and N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-activated neutrophils in suspension were used as a model for initial chemotactic activation of neutrophil locomotion. D-glucose, but not the non-metabolizable analogue 3-O-methyl-D-glucose, dose-dependently reduced the fMet-Leu-Phe-induced (10−8M) neutrophil elongation. Insulin, either alone or in combination with 25 mM D-glucose, was without effect on the fMet-Leu-Phe-induced neutrophil elongation. Furthermore, the inhibitory effect of D-glucose was observed already after 1 min of exposure to D-glucose and fMet-Leu-Phe. D-glucose diminished the fraction of neutrophils with elongated locomotor shape by changing it into an irregular cell shape, suggesting that at least part of the D-glucose effect could be associated with mechanisms determining the typical locomotor shape. The present results suggest that D-glucose through its metabolism, but without the involvement of insulin, reduces chemotactically induced elongation to a locomotor neutrophil shape, and thus neutrophil motility, and that this effect of glucose appears prior to adhesion. This glucose-induced inhibition of the neutrophil chemotactic response may be involved in the neutrophil deficiency seen in diabetes mellitus.
Erythrocyte Membrane Digoxin-Sensitive (Na+–K+)-ATPase of Non-Insulin Dependent Diabetic Humans
Authors: Okegbile E. O. , Odusan O. , Adeola O.
Published: November 2003

Erythrocyte plasma membranes of non-insulin dependent diabetic humans (NIDDM) and healthy humans were prepared by hypotonic lysis. The specific activity of (Na+-K+)-ATPase of NIDDM membranes, both in the absence and presence of digoxin were lower than the specific activity of normal enzymes (83.6 percent and 74.0 percent of the normal enzyme respectively). Addition of digoxin decreased the activity of this enzyme (38.0 percent in NIDDM and 30.0 percent in normal enzyme).

Although the affinity of the pump for ATP was similar in both membranes of NIDDM and normal humans (Km for ATP=19.9±0.24μM ATP and 20.0±0.21 μM ATP respectively), the Vmax of NIDDM membranes was more than 20 percent lower than that of the normal enzyme. The specific activity of Mg2+-dependent Ca2+-pumping ATPase (Ca2+-Mg2+)-ATPase) of NIDDM membrane was lower than 80 percent of the specific activity of the normal enzymes. While the affinity of the pump for ATP was lower in the membranes of NIDDM (Km for ATP=50.0±4.3 μM ATP) in comparison to normal membranes (Km for ATP=63.1±38μM ATP), the Vmax of NIDDM membranes was similar to the normal enzyme. Altogether, these findings suggest that both the (Na+-K+)-ATPase and Ca2+-pumping ATPase of NIDDM membranes are less functional than the enzymes in normal erythrocytes.
An Uncoupling of the Processes of Oxidation and Phosphorylation in Glycolysis
Authors: Schmalhausen Elena V. , Muronetz Vladimir I.
Published: November 2003

Data on alterations of the properties of glyceraldehyde-3-phosphate dehydrogenase upon oxidation of its functional groups are reviewed; a mechanism of uncoupling of oxidation and phosphorylation in glycolysis is considered. Possible ways of regulating uncoupling, and the physiological importance of this process, are discussed.
Transient Energy Coupling Between Rhizobia and Legume Cells Mediated by the Peribacteroid Membrane ATPase Proton Pump
Authors: Corzo Javier , Santamaria Mónica , Gutierrez-Navarro Angel M.
Published: November 2003

We present a model for the metabolic coupling between rhizobia and plant cell in the nitrogen-fixing legume root nodules. The symbiosome, an organelle-like structure formed by the modified rhizobia (the bacteroids) enclosed by a plant cell derived peribacteroid membrane, is an unique structure in which two energized membranes are closely packed: the inner bacteroid membrane and the peribacteroid membrane that possesses an ATPase proton pump. The model is based on the following points: (i) The permeability for hydrogen ions of the outer membrane of the rhizobia. (ii) The reversibility of the ATPase proton pump of the peribacteroid membrane [Szafran, M. M. and Haaker, H. (1995) Plant Physiol. 108, 1227–1232]. (iii) The relative affinites for oxygen of the bacteroid and plant mitochondria terminal oxidases, and the prevailing oxygen concentration inside the nodule, which results in aerobic metabolism for the bacteroid, but in quite fermentative catabolism for the host plant cell. We propose that the bacteroid can transiently supply free energy to the plant cell in the form of protonmotive force by the movement of hydrogen ions from the bacteroid periplasmic space to the plant cytoplasm through the peribacteroid membrane ATPase. The proposed hydrogen ion flux could be dependent on the phosphorylation potential in both the plant cell cytoplasm and the bacteroid, and the simultaneous ion movements to avoid the development of opposite Δψ. It could be important in situations of transient ATP depletion inside plant cell, which involves the block of ammonia assimilation and, subsequently, the inhibition of bacteroid nitrogenase.
Imprinting Effects of Proline Containing Dipeptides (Proline-Glycine, Proline-Leucine, Proline-Valine and Their Retro Variants) in Tetrahymena. Evolutionary Conclusions
Authors: Csaba G. , Kovács P.
Published: November 2003

Proline-glycine, proline-leucine and proline-valine dipeptides and their retro variants were used in the experiments to study the effects of pretreatment (imprinting) in Tetrahymena, by investigating fluorescein isothiocyanate (FITC)-conjugated peptide binding. The protozoan organism could differentiate between the proline-dipeptides containing different partner amino-acids and between the dipeptides having the amino acids in reversed positions. The effect of imprinting was positive or negative and this was dependent on the type of the partner amino acid and on its position. Pro-Gly and Pro-Leu induced positive imprinting (elevated FITC-dipeptide binding) and Pro-Val induced negative imprinting (decrease of FITC-peptide binding). There was positive imprinting induction in two cases for the retro FITC-peptide and in one case for the FITC-conjugate of the imprinter peptide itself. The highest positive imprinting (almost 60% increase) was induced by Pro-Gly for FITC-Gly-Pro. Considering earlier—chemotaxis—experiments, the results of the present—binding—studies run parallel with the physiological effects. The experiments call attention to the sharp differentiating ability of small peptides at a unicellular level, that could have some role in the selection of molecules for hormone formation, during evolution.
Lysyl Oxidase, Cellular Senescence and Tumor Suppression
Authors: Sharma Rashmi , Kramer Jeffrey A. , Krawetz Stephen A.
Published: November 2003

Replicative senescence may provide a mechanism of tumor suppression and tumor suppressor genes of the extracellular matrix, like lysyl oxidase, may play a role in cellular senescence. To test this hypothesis and determine whether the extracellular matrix may serve as a marker, the steady-state levels of human lysyl oxidase, α-I type III collagen and β-actin transcripts were assessed in various cell lines during in vitro passge. Northern hybridization analysis showed a significant increase in the levels of progeria fibroblast extracellular matrix mRNAs immediately preceding senescence. The levels of these mRNAs were unaffected in age-matched normal fibroblast and fetal fibroblast cell lines.
Apoptosis Dependent Decrease of the Intramembrane Ion Traffic in Cultured Mouse Fibroblasts Shown by Conductivity Dispersion
Authors: Bonincontro Adalberto , Iacoangeli Anna , Melucci-Vigo Gianna , Risuleo Gianfranco
Published: November 2003

We have investigated the intramembranal ion traffic in apoptotic 3T6 cells in culture. Apoptosis was induced by various treatments, such as serum deprivation, high density growth and hydrogen peroxide at subnecrotic doses. Cell death was assessed by nucleosomal DNA fragmentation, single cell electrophoresis, immunofluorescence and histological staining. To study the modifications of membrane structure and function, we adopted a well established biophysical strategy based on the measurement of the electrical conductivity of cell suspensions, as a function of the frequency of the electrical field applied to the sample. A comparison between the conductivity of normal and apoptotic cell suspensions shows that programmed cell death causes a decrease of membrane conductivity which indicates a diminished intramembranal ion traffic. Our results strongly suggest that one of the early events in the triggering of apoptosis is represented by an overall reduction of plasma membrane function. Finally, our results are in agreement with the idea that the nucleus is not the sole target of the apoptotic process.
Photoreceptor Guanylate Cyclases: A Review
Authors: Pugh Edward N. , Duda Teresa , Sitaramayya Ari , Sharma Rameshwar K.
Published: November 2003

Almost three decades of research in the field of photoreceptor guanylate cyclases are discussed in this review. Primarily, it focuses on the members of membrane-bound guanylate cyclases found in the outer segments of vertebrate rods. These cyclases represent a new guanylate cyclase subfamily, termed ROS-GC, which distinguishes itself from the peptide receptor guanylate cyclase family that it is not extracellularly regulated. It is regulated, instead, by the intracellularly-generated Ca2+ signals. A remarkable feature of this regulation is that ROS-GC is a transduction switch for both the low and high Ca2+ signals. The low Ca2+ signal transduction pathway is linked to phototransduction, but the physiological relevance of the high Ca2+ signal transduction pathway is not yet clear; it may be linked to neuronal synaptic activity. The review is divided into eight sections. In Section I, the field of guanylate cyclase is introduced and the scope of the review is briefly explained; Section II covers a brief history of the investigations and ideas surrounding the discovery of rod guanylate cyclase. The first five subsections of Section III review the experimental efforts to quantify the guanylate cyclase activity of rods, including in vitro and in situ biochemistry, and also the work done since 1988 in which guanylate cyclase activity has been determined. In the remaining three subsections an analytical evaluation of the Ca2+ modulation of the rod guanylate cyclase activity related to phototransduction is presented. Section IV deals with the issues of a biochemical nature: isolation and purification, subcellular localization and functional properties of rod guanylate cyclase. Section V summarizes work on the cloning of the guanylate cyclases, analysis of their primary structures, and determination of their location with in situ hybridization. Section VI summarizes studies on the regulation of guanylate cyclases, with a focus on guanylate cyclases activating proteins. In Section VII, the evidence about the localization and functional role of guanylate cyclases in other retinal cells, especially in “on-bipolar” cells, in which guanylate cyclase most likely plays a critical role in electrical signaling, is discussed. The review concludes with Section VIII, with remarks about the future directions of research on retinal guanylate cyclases.
Superoxide Production by the Mitochondrial Respiratory Chain
Authors: Turrens Julio F.
Published: November 2003

This mini-review describes the role of different mitochondrial components in the formation of reactive oxygen species under normal and pathological conditions and the effect of inhibitors and uncouplers on superoxide formation.
The Non-Ohmic Proton Leak—25 Years On
Authors: Nicholls David G.
Published: November 2003

The proton conductance of the mitochondrial inner membrane can be quantified by applying Ohm's law to the experimentally determined protonmotive force and the proton current flowing around the proton circuit in the absence of ATP synthesis or ion transport. This last parameter is derived from the rate of State 4 respiration multiplied by the H+/O stoichiometry for the substrate. When the activity of the dehydrogenase supplying electrons to the respiratory chain is progressively increased the proton conductance increases rapidly when the protonmotive force is greater than 220 mV. The consequences of this non-ohmic relationship are discussed.
Hyperthyroidism and Mitochondrial Uncoupling
Authors: Luvisetto S.
Published: November 2003

During the past years many efforts have been made to elucidate the origin of the uncoupling mechanisms induced by hyperthyroidism in mitochondria. Two main mechanisms have been proposed: a classical protonophoric uncoupler mechanism, considering the action of thyroid hormones at the level of the lipid membrane bilayer, and a slipping mechanism with more localized effects at the level of the redox proton pumps. This short review is devoted to comparing and discussing the evidence against and in favour of these two mechanisms.
“Mild” Uncoupling of Mitochondria
Authors: Starkov A. A.
Published: November 2003

Recently, it was proposed that the thyroid hormone-mediated uncoupling in mitochondria is involved in the cellular defence system against free radicals (Skulachev V.P. (1996) Quart. Rev. Biophys. 29:169–202). This phenomenon was named “mild” uncoupling. It was postulated to be a protein-mediated process controlled by several factors. The data reported during the past 40 years, pointing to the protein-mediated uncoupling mechanism in mitochondria, are reviewed in a context of hypothetical properties of “mild” uncoupling. The mechanism of “mild” uncoupling is suggested to be the following: (a) mitochondria possess protein(s) that regulate the proton permeability of inner mitochondrial membrane; (b) these proteins are regulated by binding of an unidentified low-molecular-weight endogenous compound with properties resembling those of the most active artificial uncouplers like FCCP and SF6847; (c) the interaction of this compound with its target protein(s) is modulated by a thyroid hormone in a positive (i.e. enhancing the proton permeability) way and by sex steroid hormones in a negative way; (e) endogenous fatty acids can attenuate the influence of both thyroid and steroid hormones.
Nucleotide Transport Through the Cystic Fibrosis Transmembrane Conductance Regulator
Authors: Cantiello Horacio F.
Published: November 2003

The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the superfamily of ATP-binding cassette (ABC) transporters, also known as traffic ATPases, which are implicated in the movement of various substrates. Recent studies indicate that CFTR and other closely related ABC transporters are also implicated in the movement of cellular ATP. This is the subject of current controversy. Therefore, evidence for the movement of cellular nucleotides by expression of CFTR and related molecules, as well as the potential significance of ATP-permeable channels in cell physiology, are reviewed in this study. The hypothesis is thus forwarded for the improper delivery of cellular ATP to the extracellular milieu by a dysfunctional CFTR, to be a relevant factor in the onset of cystic fibrosis.
Superoxide-Driven Aconitase FE-S Center Cycling
Authors: Gardner Paul R.
Published: November 2003

O−2 produced by the autoxidation of respiratory chain electron carriers, and other cellular reductants, inactivates bacterial and mammalian iron-sulfur-containing (de)hydratases including the citric acid cycle enzyme aconitase. Release of the solvent-exposed iron atom and oxidation of the [4Fe-4S]2+ cluster accompanies loss of catalytic activity. Rapid reactivation is achieved by iron-sulfur cluster reduction and Fe2+ insertion. Inactivation-reactivation is a dynamic and cyclical process which modulates aconitase and (de)hydratase activities in Escherichia coli and mammalian cells. The balance of inactive and active aconitase provides a sensitive measure of the changes in steady-statO−2 levels occuring in living cells and mitochondria under stress conditions. Aconitases are also inactivated by other oxidants including O2, H2O2, NO., and ONOO− which are associated with inflammation, hyperoxia and other pathophysiological conditions. Loss of aconitase activity during oxidant stress may impair energy production, and the liberation of reactive iron may further enhance oxidative damage. Iron-sulfur center cycling may also serve adaptive functions by modulating gene expression or by signaling metabolic quiescence.
Redox Regulation of the Mitochondrial Permeability Transition Pore
Authors: Chernyak B. V.
Published: November 2003

The recent data on redox regulation of the mitochondrial cyclosporin-sensitive pore are reviewed here. They indicate that the pore is modulated by the redox state of pyridine nucleotides and glutathione at two independent sites. Special attention is paid to experimental approaches for studying this phenomenon in isolated mitochondria. The relation between oxidative stress and the opening of the mitochondrial pore in some cases of cell injury and in programmed cell death (apoptosis) is discussed.
The GS-X Pump in Plant, Yeast, and Animal Cells: Structure, Function, and Gene Expression
Authors: Ishikawa Toshihisa , Li Ze-Sheng , Lu Yu-Ping , Rea Philip A.
Published: November 2003

This review addresses the recent molecular identification of several members of the glutathione S-conjugate (GS-X) pump family, a new class of ATP-binding cassette (ABC) transporters responsible for the elimination and/or sequestration of pharmacologically and agronomically important compounds in mammalian, yeast and plant cells. The molecular structure and function of GS-X pumps encoded by MRP, cMOAT, YCF1. and AtMRP genes, have been conserved throughout molecular evolution. The physiologic function of GS-X pumps is closely related with cellular detoxification, oxidative stress, inflammation, and cancer drug resistance. Coordinated expression of GS-X pump genes, e.g., MRP1 and YCF1, and γ-glutamylcystaine synthetase, a rate-limiting enzyme of cellular glutathione (GSH) biosynthesis, has been frequently observed.
Reactive Oxygen and Nitrogen Species Regulate Mitochondrial Ca2+ Homeostasis and Respiration
Authors: Richter Christoph
Published: November 2003

The reduction of molecular oxygen to water provides most of the biologically useful energy. However, oxygen reduction is a mixed blessing because incompletely reduced oxygen species such as superoxide or peroxides are quite reactive and can, when out of control, cause damage. In mitochondria, where most of the oxygen utilized by eukaryotic cells is reduced, the dichotomy of oxygen shows itself best. Thus, reactive oxygen is a threat to them, as is evident from oxidative damage to mitochondrial lipids, proteins, and nucleic acids. Reactive oxygen, in the form of peroxides, also serves useful functions in mitochondria. This is exemplified by the control of mitochondrial and cellular calcium homeostasis, whose understanding has improved greatly during the last few years. An exciting new aspect is the discovery that nitric oxide and congeners have an enormous impact on mitochondria. Physiological concentrations of nitrogen monoxide (NO) at physiological cellular oxygen pressure inhibit cytochrome oxidase and thereby respiration. A transient inhibition of cytochrome oxidase by NO appears to be used in at least some forms of cell signalling. Peroxynitrite, the product of the reaction between superoxide and NO, can stimulate the specific calcium release pathway from mitochondria by oxidizing some vicinal thiols in mitochondria. There is evidence mounting that mitochondrial calcium handling and its modulation by reactive oxygen and nitrogen species is important for necrotic and apoptotic cell death.
Structure and Function of the Plant Alternative Oxidase: Its Putative Role in the Oxygen Defence Mechanism
Authors: Wagner Anneke M. , Moore Anthony L.
Published: November 2003

Current understanding of the structure and function of the plant alternative oxidase is reviewed. In particular, the role of the oxidase in the protection of tissues against oxidative stress is developed.
Generation of H2O2 by Human Neutrophils and Changes of Cytosolic Ca2+ and pH of Rat Thymocytes in Response to Galactoside-Binding Proteins (Lectins or Immunoglobulins)
Authors: Timoshenko A. V. , André S. , Kaltner H. , Dong X. , Gabius H.-J.
Published: November 2003

In contrast to plant agglutinins, biological activities of animal/human lectins are not well defined yet. Testing a panel of seven mammalian carbohydrate-binding proteins we have found that the dimeric lectin from chicken liver (CL-16) was a stimulator of H2O2 release from human neutrophils as well as effector for induction of cytosolic Ca2+ and pH increase in rat thymocytes. Activity of this lectin was comparable to potent galactoside-specific plant lectins such as Viscum album L. agglutinin. The activities of the tested plant lectins depended significantly on their nominal carbohydrate specificity as well as on the source. The results indicate that endogenous lectins may be involved in the regulation of neutrophil and lymphocyte functions by elicitation of selective biosignaling reactions.
Mechanisms of Oxygen Taxis in Bacteria
Authors: Grishanin Ruslan N. , Bibikov Sergei I.
Published: November 2003

Since 1881 when Englemann reported aerotaxis in bacteria, an understanding of the molecular nature of the signal transduction remains a daring goal for microbiologists. This short review discusses known facts and recent advances in the field including the discovery of the flavoprotein receptor which drives Escherichia coli towards oxygen. Possible mechanisms of oxygen sensing in various bacterial species are considered in connection with the existing, often fragmental, data on phototaxis, redox taxis and taxis repellent effect of the reactive oxygen species (ROS).
The Terminal Oxidase in the Marine Bacterium Pseudomonas nautica 617
Authors: Simpson Helen , Denis Michel , Malatesta Francesco
Published: November 2003

The molecular properties of a novel membrane quinol oxidase from the marine bacterium Pseudomonas nautica 617 are presented. The protein contains 2b hemes/mole which may be distinguished by EPR spectroscopy but not by optical spectroscopy and electrochemistry. Respiration, though being cyanide insensitive, is not inhibited by carbon monoxide and oxygen reduction is carried out only half-way with production of hydrogen peroxide. The terminal oxidase represents, therefore, a unique example in the large family of terminal oxidases known up to date.
Effects of D-Glucose on Chemokinesis and Resting Production of Reactive Oxygen Species in Neutrophil Granulocytes of Lean or Obese-Hyperglycemic Mouse
Authors: Oldenborg Per-Arne , Sehlin Janove
Published: November 2003

The response to D-glucose (0–21 mM) was studied in neutrophil granulocytes from obese, hyperglycemic and hyperinsulinemic Umeå ob/ob mice and their lean, littermate controls in order to further elucidate the effects of in vivo and in vitro hyperglycemia on neutrophil function. Neutrophil random locomotion on glass and neutrophil resting luminol-enhanced chemiluminescence in cell suspension were studied. Random locomotion was stimulated by D-glucose in neutrophils from both Umeå ob/ob and control mice but the locomotive activity in Umeå ob/ob mouse neutrophils was significantly higher than that found in the controls at 4–21 mM glucose. In both types of mice, the stimulatory effect of D-glucose on random locomotion was diminished at 21 mM glucose (not significantly different from that at 0 mM glucose). Resting chemiluminescence from mouse neutrophils was also stimulated by glucose but here the magnitude of response was similar in neutrophils from both types of mice. These results indicate that chronic hyperglycemia and hyperinsulinemia in the Umeå ob/ob mouse may be associated with an increased neutrophil random locomotive activity but a similar resting production of reactive oxygen species, as compared with neutrophils from control mice at physiological and hyperglycemic glucose concentrations in vitro.
Dynamic and energetic coupling in the equatorial ionosphere and thermosphere
Authors: Maruyama N. , Watanabe S. , Fuller‐Rowell T. J.
Published: November 2003

A three‐dimensional coupled model of the global ionosphere and thermosphere has been used to examine the importance of ion drag parallel to the geomagnetic field, on the equatorial wind and temperature structure. Simulations performed at equinox, moderate solar activity (F10.7 = 150), and geomagnetically quiet condition (Ap = 7) show that the model reproduces the general observed structures of the global ionosphere and thermosphere. Comparison between the model results and satellite observations confirms that ion drag plays a significant role in the zonal momentum balance and superrotation of the Earth's upper atmosphere at equatorial latitudes. The results also suggested that ion drag parallel to the field lines, in the vicinity of a pronounced Equatorial Ionization Anomaly, has a significant impact on the latitudinal structure of the equatorial neutral wind and temperature structure. Note that the impact of parallel ion drag on the wind and temperature structure has not been evaluated previously. The model simulations show that the ion motion parallel to the field lines acts as a source of momentum to the neutral atmosphere. It is well established that after being transported upward by electric fields at the magnetic equator, plasma falls along the inclined field lines either side. The simulations indicate that collisions between the falling plasma and neutrals impart a small momentum source forcing poleward winds away from the magnetic equator. The neutral wind in turn transports momentum and energy and produces adiabatic changes that alter the meridional temperature structure. The results show that the impact of parallel ion drag must be considered in any comprehensive analysis of dynamics and energy coupling of the equatorial ionosphere and thermosphere and is important when interpreting observations of equatorial wind and temperature features, such as ETWA or MTM.
Ocean wind fields retrieved from radar‐image sequences
Authors: Dankert H. , Horstmann J. , Rosenthal W.
Published: November 2003

The dependency of radar backscatter on the surface wind field is investigated using a nautical X‐band radar operating at grazing incidence and horizontal polarization in transmit and receive. This resulted in development of an algorithm for wind retrieval from nautical radar image sequences. The algorithm consists of two parts: In the first part, wind directions are extracted from wind‐induced streaks that are in line with the mean surface wind direction. These streaks are visible in the temporal integrated radar images at scales between 100 and 500 m. The orientation of the streaks is determined from the local gradients, which are derived from the radar images smoothed and reduced to the appropriate scales. In the second part, wind speeds are derived from the backscatter of the temporal integrated radar image sequence and the radar retrieved wind direction. The dependency of the radar backscatter on the local surface wind and geometry of the radar is parameterized by training a neural network. The algorithm is applied to radar image sequences acquired by a nautical X‐band radar mounted aboard an offshore platform in the North Sea. The radar‐derived winds are validated by comparison to in situ wind data measured at the platform. The comparison of wind directions resulted in a correlation of 0.99 with a standard deviation of 14.2°; for wind speeds the correlation is 0.97 with a standard deviation of 0.85 m s−1. In contrast to traditional offshore wind sensors, the retrieval of the wind field from the backscatter of the ocean surface makes the system independent of the sensors motion and installation height and reduces the effects due to platform‐induced blockage and turbulence effects.
X‐ray structure and activity of the yeast Pop2 protein: a nuclease subunit of the mRNA deadenylase complex
Authors: Thore Stéphane , Mauxion Fabienne , Séraphin Bertrand , Suck Dietrich
Published: November 2003

In Saccharomyces cerevisiae, a large complex, known as the Ccr4–Not complex, containing two nucleases, is responsible for mRNA deadenylation. One of these nucleases is called Pop2 and has been identified by similarity with PARN, a human poly(A) nuclease. Here, we present the crystal structure of the nuclease domain of Pop2 at 2.3 Å resolution. The domain has the fold of the DnaQ family and represents the first structure of an RNase from the DEDD superfamily. Despite the presence of two non‐canonical residues in the active site, the domain displays RNase activity on a broad range of RNA substrates. Site‐directed mutagenesis of active‐site residues demonstrates the intrinsic ability of the Pop2 RNase D domain to digest RNA. This first structure of a nuclease involved in the 3′–5′ deadenylation of mRNA in yeast provides information for the understanding of the mechanism by which the Ccr4–Not complex achieves its functions.
Strategy for orchard use of Bacillus thuringiensis while minimizing impact on Choristoneura rosaceana parasitoids
Authors: Cossentine J.E. , Jensen L.B. , Deglow E.K.
Published: November 2003

Trials were conducted to study how spring Bacillus thuringiensis Berliner subsp. kurstaki treatments on apple may be timed to maximize the survival of parasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), found in the southern interior of British Columbia, Canada. Orchard collections verified that second through fourth instar obliquebanded leafrollers were found in varying proportions from pink through the petal fall stage of apple development when spring B. thuringiensis treatments are applied vs. lepidopteran pests. Laboratory‐reared second through fourth instar obliquebanded leafrollers, unparasitized and parasitized by one of three native parasitoid species, were fed untreated apple leaves or leaves treated with B. thuringiensis. The highest mortality of unparasitized obliquebanded leafrollers occurred when fourth instars were exposed to B. thuringiensis‐treated leaves; B. thuringiensis‐induced mortality in the unparasitized second and third instars was less than 50%. The consumption of B. thuringiensis‐treated leaves by host larvae significantly increased the percentage of dead host larvae in all parasitized and unparasitized treatments. However, because of the low susceptibility of this leafroller species to B. thuringiensis, relatively high numbers (38–43%) of three obliquebanded leafroller parasitoid species were able to survive the consumption of B. thuringiensis by second and third instar host larvae. Fourth instar obliquebanded leafrollers were found at the full bloom and petal fall stage of apple development in the orchard, at which time B. thuringiensis treatments are recommended for optimal leafroller control. The highest parasitoid mortality due to host mortality was recorded in Apophua simplicipes Cresson (Hymenoptera: Ichneumonidae) and Macrocentrus linearis (Nees) (Hymenoptera: Braconidae), when the hosts were treated as fourth instars. Both of these parasitoids emerge from fifth and sixth instar obliquebanded leafrollers. Bacillus thuringiensis did not have as negative an impact on Apanteles polychrosidis Viereck (Hymenoptera: Braconidae), which emerges when the host is in the fourth instar. When leafroller mortality and parasitism were combined, the B. thuringiensis treatment did not significantly increase host elimination above that of parasitism alone, except for larvae parasitized by A. simplicipes that were in the fourth instar. The consumption of B. thuringiensis by unparasitized larvae was shown to slow larval development.