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PubMed1978

Intracellular motility of mitochondria: role of the inner compartment in migration and shape changes of mitochondria in XTH-cells.

Mitochondrial movements have been followed by phase-contrast microscopy in living XTH-cells (Xenopus laevis tadpole-heart cells) in tissue culture. The same organelles have been viewed subsequently in electron micrographs. Locomotion of mitochondria proceeds at velocities up to 100 micrometer/min. Formation of branches of mitochondria and other shape changes may occur with the same speed. Mitochondrial motility can be classified into 4 types: (I) Alternating extension and contraction at the two ends of rod-shaped mitochondria. (2) Lateral branching. (3) Alternate stretching and contraction of arbitrary parts of a mitochondrion amounting to a kind of peristaltic action. (4) Transverse wave propagation along the organelle. Types I to 3 can be reduced to the same underlying principle; they cause locomotion. Formation of mitochondrial extensions is due to elongation of cristae. The observations are discussed in terms of 4 specific proposals. (I) Intracellular locomotion of mitochondria is caused by local enlargements and contractions of the organelles. (2) The shape changes are correlated with alterations in the arrangement of the cristae. (3) Such arrangements are not associated with overall swelling or shrinkage of the mitochondrion; they are local features. (4) Estimates of the time required for rearrangement of the inner compartment amount to less than 0.3 s for single crista arrangements during the fastest shape changes, and less than 1-3 s during slower alterations. This high velocity is in good accord with the hypothesis of energy conservation by conformational events during oxidative phosphorylation.

Animals↗
PubMed1977

Mitochondrial ATPase of Zajdela hepatoma. II. Mitochondria of Zajdela hepatoma contain less adenosine triphosphatase than mitochondria of rat liver.

The specific activity and the content of ATPase in mitochondria of rat liver and Zajdela hepatoma were compared. The specific activity of ATPase in sonicated mitochondria and in mitochondrial membrane fraction of rat liver was almost two times higher than the specific activity in the corresponding fraction of Zajdela hepatoma. Accordingly, the autovertin binding capacity of rat liver mitochondrial membrane fraction as well as the yield of F1-ATPase from this fraction were about two times higher than those of the mitochondrial membrane fraction of Zajdela hepatoma. The results show that mitochondria of Zajdela Hapatoma possess about half amount of ATPase present in rat liver mitochondria.

Adenosine Triphosphatases↗
PubMed1979

Effect of a polyanion macromolecule on mitochondria DNA synthesis in isolated rat liver mitochondria.

The incorporation of (3H) thymidine into isolated rat liver mitochondria in the presence of 0--0.5 mM ATP was stimulated by a polyanion with an average molecular weight of 10 000 daltons (at 50--200 micrograms/ml concentration) and containing in a proportion of 1 : 2 : 3 methacrylate, maleate and styrene. The above concentrations of the polyanion inhibit the incorporation of (3H) thymidine in the presence of 2 mM ATP and have no substantial effect on (14C)isoleucine incorporation in vitro. The mtDNA synthesis stimulatory effect of the polyanion is independent of its inhibitory effect on adenylate translocase. The polyanion does not enhance the nucleotide transport across the inner membrane of the mitochondria and the changes of thymidine phosphorylating activity are not involved in the increased mtDNA synthesis. It is supposed that the polyanion attached to the inner membrane of the mitochondria alters the binding of mtDNA to the inner membrane of the mitochondria. Thus, the polyanion might be an effective tool in studying the functional significance of mtDNA-membrane association in mtDNA replication.

Acrylates↗
PubMed1982

Import of proteins into mitochondria. Translatable mRNAs for imported mitochondrial proteins are present in free as well as mitochondria-bound cytoplasmic polysomes.

In order to assess the role of different polysomal populations in mitochondrial protein import, yeast spheroplasts were treated with cycloheximide to prevent polysome "run-off" and fractionated into free polysomes, polysomes bound to the mitochondrial outer surface, and polysomes bound to the endoplasmic reticulum. These polysomes were analyzed for translatable mRNAs coding for 8 cytosolic and 12 imported mitochondrial proteins. The mitochondrial proteins included 7 proteins of the inner membrane, 2 proteins of the matrix, 2 proteins of the intermembrane space, and 1 protein of the outer membrane. Of the mRNAs for imported mitochondrial proteins, 8 were enriched in mitochondria-bound polysomes, 3 were enriched in free polysomes, and 1 was enriched in neither. All mRNAs for cytosolic proteins were enriched in free polysomes. Polysomes bound to the endoplasmic reticulum lacked significant levels of translatable mRNAs for either cytosolic or mitochondrial proteins. Even though mRNAs for imported mitochondrial proteins were enriched in mitochondria-bound polysomes, these polysomes represented only 12-18% of the total cytoplasmic polysomes. As a consequence, none of the translatable mRNAs for imported mitochondrial proteins tested was predominantly associated with mitochondria-bound polysomes. While mitochondria-bound polysomes may contribute to mitochondrial protein import, they do not appear to be obligatory for this process.

Biological Transport↗
PubMed1994

[Design of heterologous mitochondria: import of cattle cytochrome P-450SCC precursors in plant mitochondria].

It has been shown that pre-P-450scc of bovine adrenal cortex mitochondria synthesized in a rabbit reticulocyte lysate cell-free system, is translocated into isolated soybean cotyledon mitochondria, thereby taking the mature form size. This finding is suggestive of the occurrence of a specific receptor and maturase for pre-P-450scc in plant mitochondria. Thus, plant mitochondria can be used as recipients for the mammalian cholesterol hydroxylase system in an attempt to study the mechanism of its formation and preservation.

Adrenal Cortex↗
PubMed1971

The Respiratory Chain of Plant Mitochondria: IX. Oxidation-Reduction Potentials of the Cytochromes of Mung Bean Mitochondria.

The oxidation-reduction potentials of the cytochromes of the respiratory chain of mung bean (Phaseolus aureus) mitochondria have been measured under strictly anaerobic conditions with a combined spectrophotometric/potentiometric method. The midpoint potentials at pH 7.2 are as follows: cytochrome a: +190 millivolts; a(3): +380 millivolts; b(553): +75 millivolts; b(557): +42 millivolts; b(562): -77 millivolts; c(547) and c(549): +235 millivolts. (The subscripts refer to the difference absorbance maxima observed for these cytochromes in reduced-minus-oxidized difference spectra recorded at 77 K.) The same values of midpoint potentials at pH 7.2 are obtained with mitochondria depleted of energy by aerobic incubation with ADP and uncoupler in the presence of inorganic phosphate, or with coupled mitochondria energized with ATP in the absence of inorganic phosphate. Coupling site II is placed between b(553)/b(557) and c(549)/c(547) in these mitochondria, and coupling site III is placed between a and a(3).

Journal Article↗
PubMed1972

The Respiratory Chain of Plant Mitochondria: XII. Some Aspects of the Energy-linked Reverse Electron Transport from the Cytochromes c to the Cytochromes b in Mung Bean Mitochondria.

The cytochromes c of mung bean (Phaseolus aureus) mitochondria become reduced when sulfide, a cytochrome oxidase inhibitor free from uncoupling side effects, is added to the aerobic mitochondrial suspension in the absence of added substrate. The cytochromes b remain largely oxidized. Subsequent addition of ATP results in partial oxidation of the cytochromes c and partial reduction of the cytochromes b due to ATP-driven reverse electron transport through the second site of energy conservation, or coupling site, of the respiratory chain. Cytochrome a is also oxidized under these conditions, but there is no concomitant reduction of the flavoprotein components, of ubiquinone, or of endogenous pyridine nucleotide. The reaction is abolished by oligomycin. The reducing equivalents transported from the cytochromes c and a in ATP-driven reverse electron transport are about 2-fold greater than those which appear in the cytochromes b. It is suggested that the equivalents not accounted for are present in a coupling site enzyme at the second site of energy conservation which interacts with the respiratory chain carriers by means of the dithiol-disulfide couple; this couple would not show absorbance changes with redox state over the wavelength range examined. With succinate present, reverse electron transport can be demonstrated at both coupling sites in both the aerobic steady state and in anaerobiosis. ATP-driven reverse electron transport in anaerobiosis maintains cytochrome a 30% oxidized while endogenous pyridine nucleotide is 50% reduced.When mung bean mitochondria, oxidizing succinate in the presence of sulfide through the alternate, cyanide- and sulfide-insensitive terminal oxidase, become anaerobic, cytochrome b(557), which has remained largely oxidized, becomes slowly reduced. The slow reduction is observed in coupled, energized mitochondria and in uncoupled mitochondria; the time course parallels the reduction of cytochrome a(3) under the same conditions. It appears that sulfide-liganded, oxidized cytochrome a(3) may be in close enough proximity to cytochrome b(557) in the membrane to inhibit the reduction of the latter.

Journal Article↗
PubMed1974

The Respiratory Chain of Plant Mitochondria: XVI. Interaction of Cytochrome b(562) with the Respiratory Chain of Coupled and Uncoupled Mung Bean Mitochondria: Evidence for Its Exclusion from the Main Sequence of the Chain.

Cytochromes b(553), b(557), and b(562) of mung bean (Phaseolus aureus) mitochondria become partially reduced with endogenous substrate on addition of antimycin A to the aerobic mitochondrial suspension. Addition of ATP causes partial reoxidation of the three cytochromes. This partial oxidation by ATP is inhibited by oligomycin and reversed by uncoupler. Ubiquinone does not appear to act as electron acceptor for the oxidation reaction, but a nonfluorescent flavoprotein, or possibly ironsulfur protein, component does appear to act as acceptor. This is consistent with reverse electron transport driven by ATP across the first site of energy conservation of the respiratory chain. Endogenous pyridine nucleotide and the fluorescent flavoprotein with E(m7.2) = -155mv (midpoint potential at pH 7.2, referred to normal hydrogen electrode) in uncoupled mitochondria become reduced in anaerobiosis attained by oxidation of succinate in the absence of respiratory inhibitors of the cytochrome chain, provided that Pi and ATP are present. Under these same conditions, cytochrome b(557) is completely reduced but cytochrome b(562) remains nearly completely oxidized. There is no equilibration across the first site of energy conservation between the carriers on the low potential side and cytochrome b(562) with E(m7.2) = -77mv on the high potential side. It is concluded that cytochrome b(562) is not a part of the main sequence of electron transport carriers of the mitochondrial respiratory chain of plants; it can participate in redox reactions with the respiratory chain in coupled mitochondria but not in uncoupled mitochondria unless antimycin A is present.

Journal Article↗
PubMed1963

SIZE AND SHAPE TRANSFORMATIONS CORRELATED WITH OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA. I. SWELLING-SHRINKAGE MECHANISMS IN INTACT MITOCHONDRIA.

Two types of swelling-shrinkage change manifested by isolated mammalian heart mitochondria have been studied. One type, designated as phase I or "low amplitude" swelling-shrinkage, is estimated to lead to changes in mitochondrial volume of 20 to 40 per cent, to changes in light scattering of about 30 per cent, and to changes in viscosity. These physical changes in mitochondria are brought about rapidly and reversibly by normal reactants of the respiratory chain. Their speed, specificity, and reversibility indicate that they are closely geared to the normal function of the respiratory chain and are a true reflection of a mechanochemical coupling process characteristic of the physiology of mitochondria. A second type of swelling-shrinkage mechanism, designated as phase II or "high amplitude," leads to changes in light scattering, viscosity, and mitochondrial volume which, frequently but not always, are of higher magnitude than the phase I type. Phase II swelling-shrinkage seems to be only partly under the control of the respiratory chain. Prior to the completion of phase II swelling, a stepwise loss of mitochondrial function can be identified, such as changes in the rate of substrate utilization and loss of respiratory control. Reversal of this type of swelling cannot be effected if the swelling change reaches a steady state. This type of swelling may provide cells with a mechanism for destroying mitochondrial substance.

Animals↗
PubMed1963

BRAIN MITOCHONDRIA. I. ISOLATION OF BOVINE BRAIN MITOCHONDRIA.

Two methods of preparing a mitochondrial fraction from beef brain cortex are described. Data are presented on the rate of oxidation of substrates, P/O and respiratory control ratios, cholinesterase activity, and DNA content. Electron micrographs of isolated mitochondria and mitochondria in situ are shown. Comparisons are drawn between these preparations and mitochondria prepared in 0.25 M sucrose. The data on enzymic properties and contamination by non-mitochondrial material indicate that mitochondrial fractions which compare favorably with those from other tissues can be prepared from brain tissue.

Adenine Nucleotides↗
PubMed1956

Cytochemical studies of mitochondria. I. The separation and identification of a membrane fraction from isolated mitochondria.

Mitochondria isolated from rat liver and suspended in 0.44 M sucrose were disrupted by treatment with 0.3 per cent Na deoxycholate. The treated suspension was fractionated by differential centrifugation into a number of fractions and the respective pellets were examined in sections in the electron microscope. One of these fractions was found to consist of apparently membrane-bound (vesicular) elements. The difference between interfaces and membranes was discussed and the material of this fraction was found to meet stated requirements identifying it as membranous. A detailed study of the disruption process undergone by mitochondria in the presence of Na deoxycholate showed that the elements of this fraction were derived from structural elements assumed to be mitochondrial membranes. The findings thus demonstrate that mitochondria do possess membranes as defined and that these membranes can be isolated in a relatively pure form.

Animals↗
PubMed1978

Investigations on the turnover of adrenocortical mitochondria. XII. Studies on the mechanism of the ACTH-induced elongation of the half-life of rat zona fasciculata mitochondria.

The half-life of rat adrenocortical mitochondria was determined by high resolution autoradiography and liquid scintillation spectroscopy as previously described (Mazzocchi et al., '76). The results obtained by the two approaches were in good agreement. In the normal rats the half-life of adrenocortical mitochondria averaged 11 days. ACTH significantly increased mitochondrial half-life to about 16 days, and chloramphenicol significantly decreased this parameter in both untreated and ACTH-administered rats to about seven days. It is suggested that the ACTH-induced maintenance and slowing down of the degradation rate of adrenocortical mitochondria requires continuous mitochondrial DNA-dependent protein synthesis.

Adrenal Cortex↗
PubMed1984

Studies on rat liver mitochondria: 4. Enzyme activities in mitochondria preserved at 0-4 degrees C.

Rat liver mitochondria, stored with the energy-linked functions preserved or in aging conditions, were used to assay the activity of various enzymes during five days. The preservation of energy-linked functions was monitored by the respiratory control coefficient. ATPase, cytochrome oxidase and NADH dehydrogenase showed increased activity when the energy-linked functions were preserved. In aging conditions, cytochrome oxidase, NADH dehydrogenase and ATPase showed decreased activity. The ATPase activity increased only when mitochondria were stored in the presence of inhibitors of the electron transport chain. The activity of NADH oxidase did not change, and succinate oxidase and succinate dehydrogenase showed a small decrease in their activity. The enzymes of the matrix, alpha-ketoglutarate dehydrogenase, malate dehydrogenase and aspartate aminotransferase showed little decrease in activity under either of the conditions of storage. The total protein content decreased slightly under both conditions of storage. These results show that the activity of the enzymes analysed was maintained at reasonable levels, when the energy-linked functions of isolated mitochondria were preserved.

Animals↗
PubMed1978

Calcium uptake in skeletal muscle mitochondria. I. The effects of chelating agents on the mitochondria from fatigued rats.

Female Wistar rats were used to determine the effects of the chelating agents, EDTA and EGTA, on the in vitro 45Ca2+ accumulation by mitochondria isolated from the skeletal muscle of fatigued animals. The rats were divided into three groups: sedentary-rested (SR), trained-rested (TR), trained-exhausted (TE). The trained groups were exercised on a treadmill for 1 h daily, five times a week, for 22 weeks. At the conclusion of the training program, the TE group was rapidly exercised to exhaustion immediately following their daily 1-h run. In the TR group EDTA reduced 45Ca2+ binding while both EDTA and EGTA appeared to increase mitochondrial Ca2+ and Mg2+ content. In the TE group, EDTA reduced endogenous mitochondrial Ca2+ and Mg2+ content, while both EDTA and EGTA increased 45Ca2+ binding. Since chelating Ca2+ and Mg2+ from the membrane may affect the structure and function of the mitochondria, it is suggested that the use of chelating agents during the isolation of mitochondria from the skeletal muscle of trained rats be viewed with caution.

Animals↗
PubMed1975

Letters to the editor: On the transfer of nuclear RNA into isolated mitochondria. Further evidence for template properties of nuclear RNA taken up by isolated mitochondria.

Some properties of nuclear RNA taken up by isolated mitochondria during aerobic incubation were studied. Nuclear RNA fraction re-isolated from incubated mitochondria was characterized by homogeneous sedimentation distribution in sucrose gradient (7-9S) and by absence of extended secondary structure. In this respect the RNA fraction differed from the nuclear RNA added to mitochondria and was similar to in vivo rapidly labelled mitochondrial RNA. The hybridization pattern of re-isolated RNA with nuclear DNA is consistent with the presence of transcripts from unique DNA sequences in this RNA fraction.

Aerobiosis↗
PubMed1975

Energy-dependent accumulation of iron by isolated rat liver mitochondria. IV. Relationship to the energy state of the mitochondria.

1. The energy-dependent accumulation of iron by isolated rat liver mitochondria, respiring on endogenous substrates, is strongly dependent on the efficiency of energy coupling in the respiratory chain as measured by respiratory control with ADP and the endogenous energy dissipation. The accumulation reached a saturation level at respiratory control with ADP values (with succinate as the substrate) of approx. 4.0. 2. In the presence of exogenous substrate, the energy-dependent accumulation of iron was markedly reduced, primarily due to binding of iron as carboxylate complexes having less favourable constants than the iron (III)-sucrose complex(es). 3. The effect of added ATP was at least 2-fold, i.e. that of providing energy and that of chelating iron. When the mitochondria respired on endogenous substrate, the energy-dependent accumulation of iron increased at low concentrations of ATP, whereas higher concentrations (greater than 50 mu M) gradually inhibited the uptake. 4. Energization of the mitochondria by the generation of an artificial K-+ gradient across the inner membrane with valinomycin in a K-+-free medium increased the energy-dependent accumulation iron.

Adenosine Triphosphate↗
PubMed1987

The metabolism of deoxyguanosine in mitochondria: a characterization of the phosphorylation process which occurs in intact mitochondria.

Isolated, intact mitochondria were evaluated for their ability to phosphorylate deoxyguanosine. This activity was stimulated by exogenous ATP, substrates for oxidative phosphorylation or added inorganic phosphate. Inhibitors of oxidative phosphorylation lowered the levels of deoxyguanosine phosphorylation. From a Hanes plot, an apparent Km of 0.83 microM deoxyguanosine was calculated for the phosphorylation activity in intact mitochondria. In the presence of a 20-fold excess of added deoxynucleosides, none of those tested were strongly inhibitory. However, added UDP and dTDP were stimulatory and dGTP and dGDP were inhibitory to the phosphorylation of deoxyguanosine. These data show that mitochondria phosphorylate deoxyguanosine and that the process is regulated by other events which take place within the organelle.

Adenosine Diphosphate↗
PubMed1992

Ultrastructural aspects and amino acid composition of the purified inner and outer membranes of human liver mitochondria as compared to rat liver mitochondria.

1. The mitochondria isolated from human or rat liver were fractionated into submitochondrial particles and purified inner and outer membrane. According to different marker enzymes the inner membranes were enriched about 5-6-fold and the outer membranes about 12-14-fold. The electron microscopical appearance of the membranes was that expected on the basis of enzymic characterization. 2. A comparison of the average amino acid composition of the membrane proteins from the two types of mitochondria has been made. In the case of submitochondrial particles there were statistically significant differences between the human and rat hydrolysates for only five amino acids. Analysing the purified mitochondrial membranes there were significant differences between the two species for nine amino acids in the case of outer membranes and for 12 amino acids in the case of inner membranes. 3. With one exception all amino acids that were increased or decreased in the outer membrane exhibited a similar trend in the inner membrane of human compared with rat liver mitochondria. It appears that liver mitochondrial membranes have a species-dependent pattern of amino acid composition of their proteins.

Amino Acids↗