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[Quantitative determination of the rate of superoxide radical formation in mitochondrial membranes by electron paramagnetic resonance].

The reaction of hydroxylamine (1-hydroxy-2,2,6,6-tetramethyl-4-oxopiperidine) with O2-. resulting in the stable nitroxyl radical formation recorded by ESR-technique was applied to estimate quantitatively the rate of O2-. superoxide radical generation (VO2.-) by submitochondrial particles (SMP) of liver (of mice and rats). The VO2.- dependence on concentrations of NADH, succinate and protein of SMP was established. The method allows detecting VO2.- greater than 0.05 nmol.min-1.ml-1. It has been shown that in the NADH-dependent site of the chain VO2.- is 3-4 times that in the succinate-dependent site. In the presence of rhotenone and antimycin A VO2.- increases by 30-35%, while cyanide retards VO2.- by about 30%. The data comparison with regard to VO2.- and O2 absorption rate polarographically determined has indicated that about 2% of the absorbed O2 is consumed to form O2-.

Animals↗

Regulation of the Pi-ATP exchange and hydrolytic reactions in F0-F1 reconstituted liposomes.

The regulation of ATP hydrolysis and Pi-ATP exchange reactions by ATP, ADP, Mg2+, and phosphate was studied in liposomes containing F0-F1 obtained from bovine heart submitochondrial particles by solubilization with lauryl dimethylamino oxide as described previously (Dreyfus, G., Celis, H., and Ramirez, J. (1984) Anal. Biochem. 142, 215-220). A simultaneous analysis of ATP hydrolysis and the Pi-ATP exchange reactions showed that the ratio of hydrolysis/exchange is close to one when the ATP concentration is in the lower micromolar range. In this preparation ADP stimulates the Pi-ATP exchange reaction and depresses ATP hydrolysis. The exchange reaction is almost abolished when ADP is removed from the medium by an ATP-regenerating system. Mg2+ in millimolar concentrations stimulates Pi-ATP exchange, and at the same time decreases ATP hydrolysis; accordingly, the hydrolysis/exchange ratio depends on the concentration of Mg2+. Inorganic phosphate also controls this ratio, a lower ratio being observed at high phosphate concentrations. The Pi-ATP exchange reaction, but not ATP hydrolysis, depends on the concentration of medium phosphate. These results indicate that the kinetic characteristics of this F0-F1 preparation are modified by Mg2+, ATP, and phosphate.

Adenosine Diphosphate↗

Reconstitution of mitochondrial F0.F1-ATPase with phosphatidylcholine using the nonionic detergent, octylglucoside.

A reconstitution procedure has been developed for the incorporation of the mitochondrial F0.F1-ATPase into the bilayer of egg phosphatidylcholine vesicles. The nonionic detergent, octylglucoside, egg phosphatidylcholine, and the lipid-deficient, oligomycin-sensitive F0.F1-ATPase (Serrano, R., Kanner, B., and Racker, E. (1976) J. Biol. Chem. 251, 2453-2461) were combined in a 4770:320:1 detergent/phospholipid/protein molar ratio and then centrifuged on a discontinuous sucrose gradient to isolate the F0.F1-phosphatidylcholine complex. The specific activity of the reconstituted F0.F1-ATPase was as high as 14.5 mumol/min/mg protein, whereas with no added lipid the activity ranged between 1.4 and 2.2 mumol/min/mg protein. This reconstituted preparation exhibited greater than 90% oligomycin sensitivity which demonstrated the intactness of the multisubunit enzyme complex. The phosphatidylcholine/protein molar ratio of the reconstituted F0.F1 was 250:1 with less than 0.4% of the added octylglucoside remaining. Titrations with both phosphatidylcholine and octylglucoside demonstrated that the specific activity and oligomycin sensitivity were highly dependent on the concentrations of both phospholipid and detergent in the original reconstitution mixture. Analysis of the reconstituted ATPase by electron microscopy demonstrated that the catalytic portion of the enzyme complex projected from the phospholipid bilayer with an orientation similar to that observed with submitochondrial particles. The F0.F1-phosphatidylcholine complex was able to trap inulin, which suggests a vesicular structure impermeable to macromolecules. The electrophoretic mobility of the complex was identical to that for liposomes of egg phosphatidylcholine alone. The reconstitution conditions utilized give rise to an enzyme-phospholipid complex with very low ionic charge that demonstrates high oligomycin-sensitive ATPase activity.

Animals↗

Kinetic modalities of ATP synthesis. Regulation by the mitochondrial respiratory chain.

Two interconvertible kinetic modes are described for ATP synthesis by bovine heart submitochondrial particles. One mode is characterized by low apparent Km values for ADP (6-10 microM) and Pi (less than or equal to 0.25 mM), and a limited capacity for ATP synthesis (apparent Vmax approximately 500 nmol ATP.min-1.mg of protein-1). ATP synthesis occurs predominantly in this mode when the coupled activity of the respiratory chain relative to the number of functional ATP synthase complexes is low. The second kinetic mode is characterized by high apparent Km values for ADP (50-100 microM) and Pi (approximately 2.0 mM) and a high capacity for ATP synthesis (Vmax greater than 1800 nmol ATP.min-1.mg of protein-1). This mode of ATP synthesis predominates when the available free energy relative to the number of functional ATP synthase units is high. These results suggest that energy pressure in mitochondria might regulate ATP synthesis such that at low levels of energy the ATP synthase operates economically (low substrate Km values, low turnover capacity for ATP synthesis), while at high levels of energy these kinetic constraints are relaxed (high substrate Km values, high turnover capacity for ATP synthesis). The implications of these findings are discussed in relation to the cooperative-type kinetics of ATP synthesis and hydrolysis, the differential effects of a number of F0-F1 inhibitors on the rates of ATP synthesis and hydrolysis, and the controversy as to whether protonic energy in mitochondria is localized or delocalized.

Adenosine Triphosphatases↗

[Polymorphism of membrane proteinases from mitochondria].

Using native polyacrylamide gel electrophoresis in the absence of sodium dodecyl sulfate, the detergent extracts of sonic submitochondrial particles (SMP) were separated into three protein fractions capable of accomplishing the proteolysis of cytochrome c and three other fractions catalyzing the hydrolysis of N-a-benzoyl-L-arginine-p-nitroanilide (BAPA) and N-a-benzoyl-L-arginine-B-naphthylamide (BANA). The fractions isolated from the gel were subjected to a thorough anaylsis. Cytochrome c hydrolases were shown to have identical molecular weights (17000) but different isoelectric points (4.0, 4.2 and 4.4). The total cytochrome c hydrolase activity of these enzymes was inhibited by phenylmethylsulfonylfluoride but was insensitive to ethylenediaminetetraacetate and o-phenanthroline. Three BANA (BAPA) hydrolases have identical Mr values (approximately 17500) but different pI values (4.2, 4.3 and 4.7). Apart from the indicated hydrolases, the detergent extracts of SMP were shown to contain minor components with identical activities distinguished by the tightness of binding to the inner mitochondrial membrane, Mr and sensitivity to proteinase inhibitors. The observed phenomenon is considered to be due to the polymorphism of proteinases coupled with the inner mitochondrial membrane.

Benzoylarginine Nitroanilide↗

Immunological comparison of the b and c1 cytochromes from bovine heart mitochondria and the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26.

Antibodies against cytochromes b and c1 of bovine heart mitochondria and the photosynthetic bacterium, Rhodopseudomonas sphaeroides R-26, were raised in rabbits. The purified antibodies showed high titers against their respective antigens in enzyme-linked immunosorbent assays. Less than 15% cross-reactivity between the mitochondrial and bacterial cytochromes was detected. Although antibodies against mitochondrial cytochrome b did not inhibit the mitochondrial cytochrome b-c1 complex, a 70% inhibition was obtained when these antibodies were incubated with delipidated mitochondrial cytochrome b-c1 complex prior to reconstitution with phospholipids indicating that the catalytic site(s) of mitochondrial cytochrome b are masked by phospholipids. On the other hand, antibodies against bacterial cytochrome b showed significant inhibition of the intact bacterial cytochrome b-c1 complex, indicating that some of the catalytic site epitopes of bacterial cytochrome b are exposed to the hydrophilic environment. Similar to antibodies against mitochondrial cytochrome b, antibodies against bacterial cytochrome b inhibited 50% activity of the mitochondrial cytochrome b-c1 complex only when they were incubated with the delipidated mitochondrial cytochrome b-c1 complex prior to reconstitution with phospholipids, indicating that the common epitopes between the cytochromes b are masked by phospholipids. Antibodies against mitochondrial and bacterial cytochromes c1 completely inhibited their respective cytochrome b-c1 complexes but no cross-immunoinhibition was observed. However, when antibodies against bacterial cytochrome c1 were incubated with the delipidated mitochondrial cytochrome b-c1 complex before reconstitution with phospholipids, a 65% inhibition was observed, indicating that the common epitopes between the cytochromes c1 were also somewhat masked by phospholipids. Antibodies against mitochondrial cytochrome c1 inhibited 70% of the succinate oxidase activity in the intact mitochondria preparation, but no inhibition was observed in submitochondrial particles, indicating that some mitochondrial cytochrome c1 epitopes are exposed to the cytoplasmic side.

Animals↗

Influence of repeated exposure to elevated environmental temperature on the activity of respiratory enzymes of rat liver mitochondria.

The paper presents studies of the activity of lipid-dependent enzymes of the respiratory chain of the liver of rats exposed to increased ambient temperature. The animals were heated in a chamber under controlled humidity (45-55% relative humidity), with forcer air flow and regulated temperature of 21 degrees +/- 1 degree C (control group) and 28 degrees +/- 1 degree C or 35 degrees +/- 1 degree C. They were affected by a relevant temperature for 7 or 14 consecutive days, 6 hrs daily. The enzymes activities were determined in a fraction of submitochondrial particles. The studies demonstrated that under the increased ambient temperature (7 X 6 hrs), the activity of the respiratory enzymes is changed. A statistically significant increase in the activity of NADH dehydrogenase, NADH cytochrome c reductase and cytochrome oxidase was found along with a decrease in the activity of succinate cytochrome c reductase and succinate dehydrogenase. On prolongation of thermal exposure (14 X 6 hrs) the activity of succinate dehydrogenase and succinate reductase: cytochrome c was further decreased. The activities of the other test enzymes did not exhibit any statistically significant differences as compared to controls. Kinetic tests of succinate dehydrogenase point to conformational changes of the enzyme when affected by an increased ambient temperature. This confirms the important role of this enzyme in the animals adaptation to thermally varying environmental conditions.

Animals↗

The reaction of cytochrome oxidase with cyanide. Preparation of the rapidly reacting form and its conversion to the slowly reacting form.

The magnitude of the slow phase of reaction of cytochrome oxidase with cyanide has been correlated with the size of the epr signal at g' = 12. This epr signal was not found in submitochondrial particles, and significant g' = 12 epr was only observed late in the purification of solubilized enzyme. The Hartzell-Beinert procedure for the purification of cytochrome oxidase (Hartzell, C.R., and Beinert, H. (1974) Biochim. Biophys. Acta 368, 318-338) has been modified so that the purified enzyme reacts in a single rapid phase with potassium cyanide and lacks the g' = 12 epr signal. This enzyme could be converted to the slowly reacting form upon incubation at low pH and/or low enzyme concentration. No procedure for the stable reversal of the process could be found. Some physical and chemical properties of the two forms of the enzyme are compared.

Cyanides↗

Subunit VII, the ubiquinone-binding protein, of the cytochrome b-c1 complex of yeast mitochondria is involved in electron transport at center o and faces the matrix side of the membrane.

The functional role and topographical orientation in the inner membrane of subunit VII, the ubiquinone-binding protein, of the cytochrome b-c1 complex of yeast mitochondria has been investigated. The apparent molecular weight of this subunit on sodium dodecyl sulfate-urea gels was calculated to be 15,500, while its amino acid composition was similar to that of the Q-binding proteins present in the cytochrome b-c1 complexes isolated from both beef heart and yeast mitochondria. The specific antibody obtained against subunit VII inhibited 30-47% of the ubiquinol-cytochrome c reductase activity in the isolated cytochrome b-c1 complex and in submitochondrial particles but had no effect on cytochrome c reductase activity in mitoplasts, mitochondria from which the outer membrane has been removed. Furthermore, the antibody against subunit VII strongly inhibited (74%) the reduction of cytochrome b by succinate in the presence of antimycin, an inhibitor of center i, but had no effect on cytochrome b reduction in the presence of myxothiazol, an inhibitor of center o. These results suggest that subunit VII, the Q-binding protein, is involved in electron transport at center o of the cytochrome b-c1 complex of the respiratory chain and that subunit VII is localized facing the matrix side of the inner mitochondrial membrane.

Amino Acids↗

The calcium-binding ATPase inhibitor protein from bovine heart mitochondria. Purification and properties.

Two ATPase inhibitor proteins were isolated together from bovine heart mitochondria by a new procedure; each was purified further. The one inhibitor is a Ca2+-binding protein. It was found to contain 2 cysteine residues/mol as well as threonine and proline residues, all of which the other inhibitor (first isolated by Pullman and Monroy (Pullman, M.E., and Monroy, G. C. (1963) J. Biol. Chem. 238, 3762-3769] lacks. Its minimal molecular weight was 6390 with 62 amino acid residues/mol, and its isoelectric point was 4.6. Besides differences in size, composition, and response to Ca2+, the two inhibitor proteins also differed in response to sulfhydryl compounds, pH, KCl, and cardiolipin. Inhibition by the two inhibitor proteins was additive. Both cross-reacted with mitochondrial ATPase from rat skeletal muscle. Calmodulin, with or without Ca2+, had no effect on the activity of either inhibitor protein. Antibody to the Ca2+-binding inhibitor protein did not interact with the Pullman-Monroy inhibitor or have any effect on its activity. The antibody interacted with intact submitochondrial particles that contained both inhibitor proteins but not with particles from which only the Ca2+-binding inhibitor had been removed. Clearly, the two inhibitors are distinct immunologically as well as in other properties. The two types of inhibitor protein were also isolated from rat skeletal muscle mitochondria by the new procedure.

Amino Acids↗

Effect of diabetes, adrenalectomy and hypophysectomy on D-3-hydroxybutyrate dehydrogenase activity and substrate oxidation by rat mitochondria.

In good agreement with previous observations, D-3-hydroxybutyrate dehydrogenase (OHBD) activity in disrupted liver mitochondria decreased significantly in chronic diabetic rats, whereas insulin treatment prevented this decrease. Similar effects were observed with kidney mitochondria. Adrenalectomy increased OHBD activity in liver and brain mitochondria from normal rats and in liver mitochondria from diabetic rats. Corticosterone depressed OHBD activity in liver mitochondria of normal rats and restored the normal level of OHBD in adrenalectomized rats. Hypophysectomy increased OHBD activity in normal rats, this effect being further increased by growth hormone administration. D-3-hydroxybutyrate (OHB) oxidation by liver mitochondria from diabetic, adrenalectomized or hypophysectomized rats varied as expected from OHBD activity in disrupted mitochondria, but to a relatively lesser degree. Submitochondrial particles from diabetic rats showed significant diminution in OHB-, succinate- and NADH-oxidase activities, whereas mitochondria from diabetic rats oxidized succinate and L-malate + L-glutamate at a slower rate than the corresponding controls.

3-Hydroxybutyric Acid↗

Energy-linked nicotinamide-nucleotide transhydrogenase. Characterization of reconstituted ATP-driven transhydrogenase from beef heart mitochondria.

The interaction between pure transhydrogenase and ATPase (Complex V) from beef heart mitochondria was investigated with transhydrogenase-ATPase vesicles in which the two proteins were co-reconstituted by dialysis or dilution procedures. In addition to phosphatidylcholine and phosphatidylethanolamine, reconstitution required phosphatidylserine and lysophosphatidylcholine. Transhydrogenase-ATPase vesicles catalyzed a 20-30-fold stimulation of the reduction of NADP+ or thio-NADP+ by NADH and a 70-fold shift of the apparent equilibrium expressed as the nicotinamide nucleotide ratio [NADPH][NAD+]/[NADP+][NADH]. In both of these respects, the transhydrogenase-ATPase vesicles were severalfold more efficient than beef heart submitochondrial particles. By measuring the ATP-driven transhydrogenase and the oligomycin-sensitive ATPase activities simultaneously and under the same conditions at low ATP concentrations, i.e. below 15 microM, the ATP-driven transhydrogenase/oligomycin-sensitive ATPase activity ratio was found to be about 3. This value is consistent with the stoichiometries of three protons translocated per ATP hydrolyzed and one proton translocated per NADPH formed and with a mechanism where the two enzymes interact through a delocalized proton-motive force.

Adenosine Triphosphate↗

[Comparative study of the C27-steroid-hydroxylating system from bovine liver mitochondria].

A method for purification of C27-steroid hydroxylating cytochrome P-450 (cytochrome P-450(27)) from bovine liver mitochondria was developed. The purification procedure included enzyme extraction from submitochondrial particles with sodium cholate, ammonium sulfate fractionation and biospecific chromatography on cholate-Sepharose and adrenodoxin-Sepharose. The resulting enzyme preparation (317-fold purification, 16% yield) was not electrophoretically homogeneous but did not contain hemoprotein admixtures. The kinetic parameters of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol 27-hydroxylation in a reconstituted system containing hepatoredoxin reductase, hepatoredoxin and cytochrome P-450(27) (Km = 23 microM, kcat = 0.3 s-1 at 25 degrees C) were determined. A reciprocal functional equivalency of hepatoredoxin reductase and adrenodoxin reductase as well as of hepatoredoxin and adrenodoxin in reconstituted systems of steroid 27-hydroxylation (liver) and cholesterol side chain cleavage (adrenal cortex) was established. This equivalency was thought to be due to the similarity in essential physico-chemical properties of reductase components which was especially well-pronounced in the case of hepatoredoxin and adrenodoxin. Estimation of the functional role of lysine, dicarboxylic acid and histidine residues in ferredoxin molecules by the chemical modification method revealed the similarity of the structural organization of their protein globules: the polar residues were shown to be essential for the maintenance of native conformation; dicarboxylic acid residues formed a binding domain for the interaction with electron transport proteins, whereas histidine residues seem to participate in electron transport. At the same time, cytochrome P-450(27) and cytochrome P-450 which split the side chain of cholesterol differ in their substrate specificity, immunochemical and catalytic properties.

Adrenal Cortex↗

Biotransformation of the carcinogen chrysazin by NADPH-microsome system.

The interactions of chrysazin, a carcinogenic anthraquinone, with electron transport systems in microsomes and mitochondria (submitochondrial particles, SMP) were studied. The NADPH-dependent oxygen uptake in microsomes was significantly enhanced by chrysazin and no such effect was observed in the NADH-dependent reactions in microsomes and SMP. The NADPH-microsome system caused a marked alteration in the visible absorption spectrum of chrysazin. These results strongly suggest that chrysazin is biotransformed selectively by the NADPH-microsome system.

Animals↗

Ion transport and respiratory control in vesicles formed from reduced nicotinamide adenine dinucleotide coenzyme Q reductase and phospholipids.

NADH-coenzyme Q reductase from bovine heart mitochondria (complex I) was incorporated into phospholipid vesicles by the cholate dialysis procedure. Mixtures of purified phosphatidylcholine and phosphatidylethanolamine were required. Oxidation of NADH by coenzyme Q1 catalyzed by the reconstituted vesicles was coupled to proton translocation, directed inward, with an H+/2e ratio greater than 1.4. Similar experiments measuring proton translocation in submitochondrial particles gave an H+/2e ratio of 1.8. The proton translocation in both systems was not seen in the presence of uncoupling agents and was in addition to the net proton uptake from the reduction of coenzyme Q1 by NADH. Electron transfer in the reconstituted vesicles also caused the uptake of the permeant anion tetraphenylboron. The rate of electron transfer by the reconstituted vesicles was stimulated about 3-fold by uncouplers or by valinomycin plus nigericin and K+ ions. The results indicate that energy coupling can be observed with isolated NADH-coenzyme Q reductase if the enzyme complex is properly incorporated into a phospholipid vesicle.

Animals↗

Purification and characterization of the 2-methyl branched-chain Acyl-CoA dehydrogenase, an enzyme involved in NADH-dependent enoyl-CoA reduction in anaerobic mitochondria of the nematode, Ascaris suum.

The 2-methyl branched-chain acyl-CoA dehydrogenase was purified to homogeneity from mitochondria of the parasitic nematode, Ascaris suum. The native molecular weight of the enzyme was estimated to be 170,000 by gel filtration. The enzyme migrated as a single protein band with Mr = 42,500 during sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggesting that the enzyme is a tetramer composed of identical subunits. The enzyme exhibited absorbance maxima at 272, 375, and 452 with a ratio 7.9:0.8:1.0, respectively. FAD content was estimated to be 0.9 mol/mol of subunit and the absorption coefficient of FAD at 452 nm was 14.1 mM-1 cm-1. The purified enzyme dehydrogenated both 2-methylbutyryl-CoA and 2-methylvaleryl-CoA with apparent Km and Vmax values of 18 microM and 1.62 mumol/min/mg and 21 microM and 1.58 mumol/min/mg, respectively. This enzyme also appeared to dehydrogenate butyryl-CoA, valeryl-CoA, and octanoyl-CoA but at a much lower rate. The enzyme did not dehydrogenate propionyl-CoA, isobutyryl-CoA, isovaleryl-CoA, and palmitoyl-CoA. Tiglyl-CoA and 2-methyl-2-pentenoyl-CoA were identified as reaction products from 2-methylbutyryl- and 2-methylvaleryl-CoA, respectively. Dehydrogenating activity with both substrates was inhibited by tiglyl-CoA, acetoacetyl-CoA, and straight chain acyl CoAs of increasing chain length. N-Ethylmaleimide and p-hydroxymercuribenzoate had little effect on dehydrogenating activity but the heavy metals Hg2+ and Ag2+ were potent inhibitors. Physiologically, the dehydrogenase functions as a branched-chain enoyl-CoA reductase. Incubations of A. suum submitochondrial particles, NADH, tiglyl-CoA, purified A. suum electron-transfer flavoprotein, and the 2-methyl branched-chain acyl-CoA dehydrogenase resulted in the rotenone-sensitive, dehydrogenase-dependent formation of 2-methylbutyryl-CoA.

Acyl-CoA Dehydrogenases↗

Activity of the respiratory inhibitor RF in human red cells in anaemia.

Stroma-free haemolysates of red cells from patients with acute or latent anaemia inhibit the NADH oxidase activity of submitochondrial particles from beef heart. The inhibitory activities appeared significantly more frequently in anaemic patients than in normal persons and are likely due to the action of a factor which is identical or similar to the inhibitory protein RF present in rabbit reticulocytes. The possible use of the inhibitor assay for clinical purpose is under discussion.

Acute Disease↗

[The role of lipids in the regulation of ATP and PPi synthesis in mitochondria].

It was demonstrated previously that mitochondria of higher and lower eukaryotes can synthesize, in the course of oxidative phosphorylation, not only ATP but also inorganic pyrophosphate (PPi). Two PPases were isolated from bovine heart mitochondria (soluble--PPase I and membrane--PPase II). Coupling PPase II, in contrast to PPase I, contains phosphatidyl choline, but PPase I is lipidized readily in the presence of different phospholipids. Reconstitution experiments of the PPi synthesis system have shown that after lipidization PPase I is able to incorporate into submitochondrial particles (SMP) and becomes a coupling factor for oxidation and PPi synthesis. It seems that phospholipid is indispensible for incorporation into the membrane and the manifestation of the coupling activity of the enzyme. The effect of lipids on the activity of soluble and membrane-bound pyrophosphatase was studied. It is shown that PPase II phospholipid is involved in the regulation of the hydrolase activity of the isolated enzyme. However, hydrolysis of PPi by SMP and its synthesis by mitochondria are affected by cooperative rearrangements of the entire lipid component of the membrane rather than by changes in the phase state of phosphatidyl choline contained in PPase II. An opposite response of ATP and PPi synthesis to changes in viscosity makes it likely that the viscosity of the mitochondrial inner membrane may control the levelling of these two processes in mitochondria.

Adenosine Triphosphate↗