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V P Skulachev

Publications and source records attributed to V P Skulachev.

At least 19 recordsLinked to original sources
PubMed1999

The antioxidant functions of cytochrome c.

Low (C(1/2) = 1.5 x 10(-7) M) concentrations of horse cytochrome c strongly inhibit H(2)O(2) production by rat heart mitochondria under conditions of reverse electron transfer from succinate to NAD(+). The effect is abolished by binding of cytochrome c with liposomes and is not prevented by SOD. Yeast cytochrome c is much less effective than the horse protein whereas acetylated horse cytochrome c is without effect. H(2)O(2) formation stimulated by antimycin A is resistant to added cytochrome c. In inside-out submitochondrial vesicles, H(2)O(2) production is suppressed by all three cytochrome c samples tested, but at higher concentrations (C(1/2) is about 5 x 10(-7) M). In vesicles, SOD abolishes the cytochrome c inhibition. We conclude that extramitochondrial cytochrome c is competent in down-regulation of the Complex I H(2)O(2) production linked to the reverse electron transfer. Such an effect is absent in the inside-out submitochondrial vesicles where another antioxidant cytochrome c function can be observed, i.e. the oxidation of O(2-*) to O(2). A possible role of cytochrome c in the antioxidant defence is discussed.

Animals↗
PubMed1999

Bacterial energetics at high pH: what happens to the H+ cycle when the extracellular H+ concentration decreases?

A decrease in the extracellular H+ concentration creates difficulties for membrane-linked energetics in bacteria employing H+ as the coupling ion. At high extracellular pH (pHo), H+ ions pumped from the cell by, say, the respiratory chain, are immediately neutralized by the alkaline extracellular medium. Under such conditions, the only driving force that might compel outer H+ ions to return to cytosol and perform their function is the electric potential difference across the cytoplasmic membrane (delta psi). However, when delta pH in the opposite direction is equal to, e.g., 2 pH units (intracellular pH = 7.5 at pHo = 9.5), delta psi would be so high that the risk of membrane electric breakdown would increase. This is why some bacteria deal with high pH by, for example, replacing H+ by Na+ as the coupling ion rather than by increasing delta psi. It has been shown in several species of bacteria that the alkalinization of the growth medium induces primary Na+ pumps (e.g. Na(+)-motive respiratory chain enzymes and Na+ ATPase). Electrogenic Na+ efflux via these pumps produces an electrochemical Na+ potential difference (delta mu Na+) composed of delta psi and delta pNa+. delta mu Na+ can be used to perform various types of membrane-linked work. The delta psi constituent of delta mu Na+ may maintain electrophoretic influx of H+ such that the alkalinization of cytoplasm is prevented. The latter function may be supported by a mechanism based on the uphill influx of Cl- instead of Na+. This seems to be the case for alkaliphilic and halophilic Natronobacter pharaonis. There is an indication that not only Na+ but also Ca2+ may substitute for H+ in Gleobacter violaceus growing at high pH.

Alkalies↗
PubMed1999

Mitochondrial physiology and pathology; concepts of programmed death of organelles, cells and organisms.

The review summarizes the present state of our knowledge concerning alternative functions of mitochondria, namely energy conservation in forms of protonic potential and ATP, thermoregulatory energy dissipation as heat, production of useful substances, decomposition of harmful substances, control of cellular processes. The recent progress in understanding of some mitochondrion-linked pathologies is described. The role of reactive oxygen species in these processes is stressed. Possible mechanisms of programmed death of mitochondrion (mitoptosis), cell (apoptosis) and organism (phenoptosis) are considered. A concept is put forward assuming that mitoptosis is involved in some types of apoptosis whereas apoptosis can be a part of a phenoptotic cascade. It is hypothesized that septic shock, as well as the stress-induced brain and heart ischemic diseases and cancer, exemplify mechanisms of phenoptosis purifying population, community of organisms or kin from dangerous or useless individuals.

Aconitate Hydratase↗
PubMed1999

Anion carriers in fatty acid-mediated physiological uncoupling.

Physiological aspects of uncoupling of oxidation and phosphorylation are reviewed in the context of involvement of mitochondrial anion carriers. It is assumed that the carriers facilitate electrophoretic translation of fatty acid anion, RCOO-, from the inner to the outer leaflet of the mitochondrial membrane, whereas back movement of the protonated fatty acid, RCOOH, from the outer to the inner leaflet represents flip-flop of RCOOH via the phospholipid bilayer of the membrane. The RCOO- transport seems to be catalyzed by the ATP/ADP and aspartate/ glutamate antiporters, dicarboxylate carrier, and uncoupling proteins (UCP1, UCP2, UCP3L, UCP3s, and plant UCP). The fatty acid uncoupling is shown to be involved in the thermoregulatory heat production in animals and plants exposed to cold, as well as in performance of respiratory functions other than ATP synthesis, i.e., formation of useful substances, decomposition of unwanted substances, and antioxidant defense. Moreover, partial uncoupling might take part in optimization of the rate of ATP synthesis in aerobic cells.

Adipose Tissue, Brown↗
PubMed1999

Phenoptosis: programmed death of an organism.

Programmed cell death (apoptosis) is well-established in many multicellular organisms. Apoptosis purifies a tissue from cells that became useless or even harmful for the organism. Similar phenomena are already described also at subcellular level (suicide of mitochondria, i.e., mitoptosis) as well as at supracellular level (degradation of some organs temporarily appearing in the course of ontogenesis and then disappearing by means of apoptosis of the organ-composing cells). Following the same logic, one may put a question about programmed death of an organism as a mechanism of purification of a kin, community of organisms, or population from individuals who became unwanted for this kin, etc. A putative mechanism of such kind is proposed to be coined "phenoptosis" by analogy with apoptosis and mitoptosis. In a unicellular organism (the bacterium Escherichia coli), three different biochemical mechanisms of programmed death are identified. All of them are actuated by the appearance of phages inside the bacterial cell. This may be regarded as a precedent of phenoptosis which prevents expansion of the phage infection among E. coli cells. Purification of a population from infected individuals looks like an evolutionary invention useful for a species. Such an invention has high chances to be also employed by multicellular organisms. Most probably, septic shock in animals and humans serves as an analog of the phage-induced bacterial phenoptosis. It is hypothesized that the stress-induced ischemic diseases of brain and heart as well as carcinogenesis if they are induced by repeated stresses also represent phenoptoses that, in contrast to sepsis, are age-dependent. There are interrelations of programmed death phenomena at various levels of complexity of the living systems. Thus, extensive mitoptosis in a cell leads to apoptotic death of this cell and extensive apoptosis in an organ of vital importance results in phenoptotic death of an individual. In line with this logic, some cases are already described when inhibition of apoptosis strongly improves the postischemic state of the organism.

Aging↗
PubMed1998

Thermoregulatory uncoupling in heart muscle mitochondria: involvement of the ATP/ADP antiporter and uncoupling protein.

Possible involvement of the ATP/ADP antiporter and uncoupling protein (UCP) in thermoregulatory uncoupling of oxidative phosphorylation in heart muscle has been studied. To this end, effects of carboxyatractylate (cAtr) and GDP, specific inhibitors of the antiporter and UCP, on the membrane potential of the oligomycin-treated mitochondria from cold-exposed (6 degrees C, 48 h) and control rats have been measured. It is found that cAtr increases the membrane potential level in both cold-exposed and non-exposed groups, the effect being strongly enhanced by cooling. As for GDP, it is effective only in mitochondria from the cold-exposed rats. In these mitochondria, the coupling effect of GDP is smaller than that of cAtr. CDP, which does not interact with UCP, is without any influence on membrane potential. The cold exposure is found to increase the uncoupling efficiency of added natural (palmitate) or artificial (SF6847) uncouplers, the increase being cAtr- and GDP-sensitive in the case of palmitate. The fatty acid-free bovine serum albumin enhances delta psi in both cold-exposed and control groups, the effect being much larger in the former case. It is concluded that in heart muscle mitochondria the ATP/ADP antiporter is responsible for the 'mild uncoupling' under normal conditions and for major portion of the thermoregulatory uncoupling in the cold whereas the rest of thermoregulatory uncoupling is served by UCP (presumably by UCP2 since the UCP2 mRNA level is shown to strongly increase in rat heart muscle under the cold exposure conditions used).

Adenosine Diphosphate↗
PubMed1998

Membrane potential generation coupled to oxidation of external NADH in liver mitochondria.

Oxidation of added NADH by rat liver mitochondria has been studied. It is found that exogenous NADH, when oxidized by rat liver mitochondria in sucrose hypotonic medium supplemented with Mg2+ and EGTA, generates a membrane potential (delta psi) even in the absence of added cytochrome c. ADP and phosphate decrease delta psi, the effect being reversed by oligomycin. Rotenone and myxothiazol do not inhibit delta psi generated by oxidation of exogenous NADH. Added cytochrome c increases the rate of the exogenous NADH oxidation and coupled delta psi formation. In sucrose isotonic medium, or in hypotonic medium without Mg2+, exogenous NADH fails to stimulate respiration and to form a membrane potential. In the presence of Mg2+, exogenous NADH appears to be effective in delta psi generation in isotonic sucrose medium if mitochondria were treated with digitonin. In isotonic KCl without Mg2+, oxidation of exogenous NADH is coupled to the delta psi formation and MgCl2 addition before mitochondria prevents this effect. In hypotonic (but not in isotonic) sucrose medium, Mg2+ makes a portion of the cytochrome c pool reducible by exogenous NADH or ascorbate. It is assumed that (i) hypotonic treatment or digitonin causes disruption of the outer mitochondrial membrane, and, as a consequence, desorption of the membrane-bound cytochrome c in a Mg2+-dependent fashion; (ii) incubation in isotonic KCI without Mg2+ results in swelling of mitochondrial matrix, disruption of the outer membrane and cytochrome c desorption whereas Mg2+ lowers the K+ permeability of the inner membrane and, hence, prevents swelling; (iii) desorbed cytochrome c is reduced by added NADH via NADH-cytochrome b5 reductase and cytochrome b5 or by ascorbate and is oxidized by cytochrome oxidase. The role of desorbed cytochrome c in oxidation of superoxide and cytoplasmic NADH as well as possible relations of these events to apoptosis are discussed.

Animals↗
PubMed1998

Fatty acids as natural uncouplers preventing generation of O2.- and H2O2 by mitochondria in the resting state.

Both natural (laurate) and artificial (m-chlorocarbonylcyanide phenylhydrazone; CCCP) uncouplers strongly inhibit O2.- and H2O2 formation by rat heart mitochondria oxidizing succinate. Carboxyatractylate, an ATP/ADP antiporter inhibitor, abolishes the laurate inhibition, the CCCP inhibition being unaffected. Atractylate partially releases the inhibition by laurate and decelerates the releasing effect of carboxyatractylate. GDP is much less effective than carboxyatractylate in releasing the laurate inhibition of reactive oxygen species (ROS) formation. Micromolar laurate concentrations arresting the ROS formation cause strong inhibition of reverse electron transfer from succinate to NAD+, whereas State 4 respiration and the transmembrane electric potential difference (delta psi) level are affected only slightly. It is suggested that (i) free fatty acids operate as natural 'mild uncouplers' preventing the transmembrane electrochemical H+ potential difference (delta muH+) from being above a threshold critical for ROS formation by complex I and, to a lesser degree, by complex III of the respiratory chain, and (ii) it is the ATP/ADP-antiporter, rather than uncoupling protein 2, that is mainly involved in this antioxidant mechanism of heart muscle mitochondria.

Animals↗
PubMed1998

Decrease in mitochondrial energy coupling by thyroid hormones: a physiological effect rather than a pathological hyperthyroidism consequence.

The effect of the in vivo thyroid status on mitochondrial membrane potential (delta psi(m)) in isolated rat hepatocytes was studies by means of a cytofluorimetric technique and the delta psi(m)-specific probe JC-1. It is shown that the delta psi(m) level decreases in the order hypothyroid > euthyroid > hyperthyroid. Polarographic measurement of the hepatocyte respiratory rates revealed an opposite trend of values: the highest respiratory rate in hepatocytes from hyperthyroid animals, the lowest in those from hypothyroid ones. This means that mitochondrial energy coupling is highest in hypothyroid hepatocytes and lowest in hyperthyroid hepatocytes. 6-Ketocholestanol added to hepatocytes failed to counterbalance the uncoupling effect of thyroid hormones on delta psi(m) and respiration rate. Under the same conditions, 6-ketocholestanol appeared to be effective in recoupling of respiration uncoupled by low concentrations of the artificial protonophore FCCP. The mechanism and possible physiological functions of the thyroid hormone-induced decrease in mitochondrial energy coupling are discussed.

Animals↗
PubMed1998

Cytochrome c in the apoptotic and antioxidant cascades.

Recent progress in studies on apoptosis has revealed that cytochrome c is a pro-apoptotic factor. It is released from its places on the outer surface of the inner mitochondrial membrane at early steps of apoptosis and, combining with some cytosolic proteins, activates conversion of the latent apoptosis-promoting protease pro-caspase-9 to its active form. Cytochrome c release can be initiated by the pro-apoptotic protein Bax. This process is blocked by the anti-apoptotic proteins Bcl-2 and Bcl-xL. The role of cytochrome c in apoptosis may be understood within the framework of the concept assuming that the evolutionary primary function of apoptosis was to purify tissues from ROS-overproducing cells. In this context, the pro-apoptosis activity of cytochrome c might represent one of the anti-oxidant functions inherent in this cytochrome. Among other cytochrome c-linked antioxidant mechanisms, the following systems can be indicated. (1) Cytochrome c released from the inner mitochondrial membrane to the intermembrane space can operate as an enzyme oxidizing O2.- back to O2. The reduced cytochrome c is oxidized by cytochrome oxidase (or in yeasts and bacteria, by cytochrome c peroxidase). (2) The intermembrane cytochrome c can activate the electron transport chain in the outer mitochondrial membrane. This bypasses the initial and middle parts of the main respiratory chain, which produce, as a rule, the major portion of ROS in the cell. (3) The main respiratory chain losing its cytochrome c is inhibited in such a fashion that antimycin-like agents fail to stimulate ROS production.

Antioxidants↗
PubMed1998

Two NADH:ubiquinone oxidoreductases of Azotobacter vinelandii and their role in the respiratory protection.

Initial steps of the Azotobacter vinelandii respiratory chain have been studied on the inside-out subcellular vesicles. Two NADH:ubiquinone oxidoreductases were revealed: (i) proton-motive, capsaicin-sensitive and oxidizing dNADH as well as NADH enzyme and (ii) enzyme non-coupled to the energy conservation, capsaicin-resistant and oxidizing only NADH. The level of the oxidoreductases strongly depends upon [O2] and [NH3] in the growth medium. Increase in [O2] results in lowering of the coupled-enzyme level and in rise of the non-coupled one. Exclusion of NH3 from the growth medium increases the level of the non-coupled enzyme whereas that of the coupled enzyme remains constant. The O2-linked control of NADH:ubiquinone oxidoreductases requires CydR, a Fnr-like regulatory protein. Summarizing the above observations with those made in this group on the terminal steps of the A. vinelandii respiratory chains, one can assume that the respiratory protection of nitrogenase could be carried out by co-operation of the non-coupled NADH:ubiquinone oxidoreductase and the "partially coupled" quinoloxidase of the bd-type. Efficiency of this chain seems to be five-fold lower than that of the usual proton-motive chain (the coupled NADH:ubiquinone oxidoreductase, the Q-cycle and cytochrome oxidase of the o-type) which is also present in A. vinelandii and operates at low [O2].

Azotobacter vinelandii↗
PubMed1998

Photophosphorylation in alkalophilic halobacterial cells containing halorhodopsin: chloride-ion cycle?

Light-driven ATP synthesis is found in cells of the alkalophilic bacterium Natronobacterium pharaonis containing halorhodopsin but deficient in H+-pumping bacteriorhodopsin. Photophosphorylation occurs with cyanide-inhibited respiratory chain as well as without cyanide in conditions with low C1- concentration in the incubation medium. Increase in C1- concentration from 0.1 to 2.35 M in the incubation medium leads to inhibition of photophosphorylation. Continuous illumination increases membrane Delta Psi if respiration is inhibited by cyanide. This effect is stimulated by DCCD, an ATPase inhibitor. These data can be explained if one suggests that halorhodopsin pumps C1- into the cells whereas C1- release from the cells through C1--ATP-synthase is coupled with the ATP synthesis (chloride-ion cycle).

Adenosine Triphosphate↗
PubMed1998

A model of O2.-generation in the complex III of the electron transport chain.

Oxidation of semiquinone by O2 in the Q cycle is known to be one of the sources of superoxide anion (O2.-) in aerobic cells. In this paper, such a phenomenon was analyzed using the chemical kinetics model of electron transfer from succinate to cytochrome c, including coenzyme Q, the complex III non-heme iron protein FeSIII and cytochromes bl, bh and cl. Electron transfers from QH2 to FeSIII and cytochrome bl were assumed to occur according to direct transfer mechanism (dynamic channelling) involving the formation of FeS(red)III-Q.- and Q.--cytochrome bl complexes. For oxidation/reduction reactions involving cytochromes bh and bl, the dependence of the equilibrium and elementary rate constants on the membrane potential (deltapsi) was taken into consideration. The rate of O2.- generation was found to increase dramatically with increase in deltapsi above the values found in State 3. On the other hand, the rate of cytochrome c reduction decreased sharply at the same values of the membrane potential. This explains experimental data that the O2.- generation at State 4 appears to be very much faster than at State 3. A mild uncoupling in State 4 can markedly decrease the superoxide generation due to a decrease in deltapsi below the above mentioned critical level. DeltapH appears to be equally effective as deltapsi in stimulation of superoxide production which depends, in fact, upon the deltamuH+ level.

Benzoquinones↗
PubMed1998

Biochemical mechanisms of evolution and the role of oxygen.

The concept formulated here presumes the existence of specific mechanisms of evolution that save intermediate (and therefore imperfect) forms of organisms from elimination by natural selection. A change in the life strategy made in situations when the appearance of a new trait worsens, rather than improves, adaptation of the organism to the changing environment can be one of these mechanisms. The concept postulates that, in such cases, K-strategy (relatively low rates of reproduction and activity in general but long life span) is replaced by r-strategy (high activity and reproduction but short life span). A decrease in the life span upon the K --> r transition is suggested to be an unavoidable consequence of an elevation of formation of toxic reactive oxygen species under conditions of increased rates of aerobic metabolism required for the increased life activity. The phenomenon of giantism of transgenic tobacco plants that overproduce a mitochondrial heat shock protein (experiments done by A. Moore) is assumed to be explained by an r --> K transition. On the other hand, a decrease in the life activity and a considerable increase in life span occurring in a nematode upon mutations inhibiting the CoQ biosynthesis (S. Hekimi) might serve as an example of a K --> r transition.

Animals↗
PubMed1998

Possible role of reactive oxygen species in antiviral defense.

The role of reactive oxygen species (ROS) participating in antiviral host defense is considered. Unlike antibacterial defense, when ROS and their derivatives act as biological weapons killing pathogenic bacteria, the function of ROS in the antiviral defense is assumed to be mediated by apoptosis. It is suggested that a cell activates generation of superoxide and hydrogen peroxide by xanthine oxidase as well as by intracellular NADPH-oxidase in response to appearance of a virus in its cytoplasm. Increase in ROS level turns on the process of programmed cell death in the infected cells. Moreover, H2O2 diffuses into the adjacent cells (due to its high membrane permeability), also inducing apoptosis (death of bystander cells). So, the infected cell and its neighbors (which are the most likely to be infected) are eliminated, thus blocking the spreading of the viral infection.

Animals↗
PubMed1997

High protonic potential actuates a mechanism of production of reactive oxygen species in mitochondria.

Formation of H2O2 has been studied in rat heart mitochondria, pretreated with H2O2 and aminotriazole to lower their antioxidant capacity. It is shown that the rate of H2O2 formation by mitochondria oxidizing 6 mM succinate is inhibited by a protonophorous uncoupler, ADP and phosphate, malonate, rotenone and myxothiazol, and is stimulated by antimycin A. The effect of ADP is abolished by carboxyatractylate and oligomycin. Addition of uncoupler after rotenone induces further inhibition of H2O2 production. Inhibition of H2O2 formation by uncoupler, malonate and ADP+Pi is shown to be proportional to the delta psi decrease by these compounds. A threshold delta psi value is found, above which a very strong increase in H2O2 production takes place. This threshold slightly exceeds the state 3 delta psi level. The data obtained are in line with the concept [Skulachev, V.P., Q. Rev. Biophys. 29 (1996), 169-2021 that a high proton motive force in state 4 is potentially dangerous for the cell due to an increase in the probability of superoxide formation.

Adenosine Diphosphate↗
PubMed1997

Inhibition of the alternative oxidase stimulates H2O2 production in plant mitochondria.

The hypothesis that a non-coupled alternative oxidase of plant mitochondria operates as an antioxygen defence mechanism [Purvis, A.C. and Shewfelt, R.L., Physiol. Plant. 88 (1993) 712-718; Skulachev, V.P., Biochemistry (Moscow) 59 (1994) 1433-1434] has been confirmed in experiments on isolated soybean and pea cotyledon mitochondria. It is shown that inhibitors of the alternative oxidase, salicyl hydroxamate and propyl gallate strongly stimulate H2O2 production by these mitochondria oxidizing succinate. Effective concentrations of the inhibitors proved to be the same as those decreasing the cyanide-resistant respiration. The inhibitors proved to be ineffective in stimulating H2O2 formation in rat liver mitochondria lacking the alternative oxidase.

Animals↗