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PubMed1991

Light-dependent ATP synthesis in mitochondria.

Light-dependent ATP synthesis was studied in an illuminated suspension of rat liver mitochondria. The action of light was shown to lead to an increase in the ATP content in the absence of oxidisable substrates and in the presence of high (hundreds of microM) ADP concentrations in the medium. At a relatively low (50 microM) ADP concentration, efficient light-dependent phosphorylation was observed in the presence of alpha-ketoglutarate. Prolonged illumination stimulated ATP hydrolysis. Rotenone, antimycin, azide, dicyclohexylcarbodiimide, and oligomycin inhibited the light-dependent phosphorylation almost completely. The level of ATP decreased under the action of 2,4-dinitrophenol in the dark but was restored by high light intensities. Blue light, 436 nm, was most efficient to produce light-dependent phosphorylation. It is assumed that quanta of vibrational excitation formed in the course of vibrational relaxation and the internal conversion of photoexcited flavoproteins and cytochromes are transferred to the ATP-synthetase and "eject" ATP from the active center, thus shifting the enzymatic reaction to ATP production.

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PubMed1986

[A unified concept of energy transduction by biochemical systems].

Electronic energy--resulting either from electron excitation or localization--is the obligatory link between the different forms of energy (light, redox, acid-base, metaphosphate-orthophosphate) transducible by biochemical systems. The key in energy coupling between any two transducing systems lies precisely in the fact that both of them share a common intermediate that cyclically participates in the overall transduction process by alternating between its electronically energized state and its unenergized basal state. All the energy-transducing biochemical systems must operate, according to their nature and character of the energization, at two midpoint redox potentials, at two pKa's, or at two phosphate transfer potentials. Three basic energy-transducing systems in bioenergetics, namely, redox, acid-base and metaphosphate-orthophosphate, couple between them through the acylium cation (Equation: see text)-carboxylate-anion (R-COO-) pair. These forms are, respectively, twice-energized and unenergized and can accept, at two energy levels, either two electrons or two protons or the orthophosphate anion (H2PO4-) and the "zwitterion" metaphosphate (approximately PO3-**). Both at the substrate level and at the membrane level, orthophosphate energization to metaphosphate, by removal of an oxide anion (O2-), brings about a decrease in pKa with the concomitant dissociation of the two protons (2 H+), whereas de-energization of metaphosphate to orthophosphate, by addition of an oxide anion, brings about an increase in pKa with the concomitant fixation of two protons. One of the greatest discoveries of bioenergetics was the introduction in cell metabolism of the one-electron redox photosystem chlorophyll a and was followed by the starting of the one-electron/one-proton redox/acid-base energy-transducing systems of the photosynthetic and respiratory electron transport chains.

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PubMed1986

Mechanism of calcium potentiation of oxygen free radical injury to renal mitochondria. A model for post-ischemic and toxic mitochondrial damage.

With a variety of forms of ischemic and toxic tissue injury, cellular accumulation of Ca2+ and generation of oxygen free radicals may have adverse effects upon cellular and, in particular, mitochondrial membranes. Damage to mitochondria, resulting in impaired ATP synthesis and diminished activity of cellular energy-dependent processes, could contribute to cell death. In order to model, in vitro, conditions present post-ischemia or during toxin exposure, the interactions between Ca2+ and oxygen free radicals on isolated renal mitochondria were characterized. The oxygen free radicals were generated by hypoxanthine and xanthine oxidase to simulate in vitro one of the sources of oxygen free radicals in the early post-ischemic period in vivo. With site I substrates, pyruvate and malate, Ca2+ pretreatment, followed by exposure to oxygen free radicals, resulted in an inhibition of electron transport chain function and complete uncoupling of oxidative phosphorylation. These effects were partially mitigated by dibucaine, a phospholipase A2 inhibitor. With the site II substrate, succinate, the electron transport chain defect was not manifest and respiration remained partially coupled. The electron transport chain defect produced by Ca2+ and oxygen free radicals was localized to NADH CoQ reductase. Calcium and oxygen free radicals reduced mitochondrial ATPase activity by 55% and adenine nucleotide translocase activity by 65%. By contrast oxygen free radicals alone reduced ATPase activity by 32% and had no deleterious effects on translocase activity. Dibucaine partially prevented the Ca2+-dependent reduction in ATPase activity and totally prevented the Ca2+-dependent translocase damage observed in the presence of oxygen free radicals. These findings indicate that calcium potentiates oxygen free radical injury to mitochondria. The Ca2+-induced potentiation of oxygen free radical injury likely is due in part to activation of phospholipase A2. This detrimental interaction associated with Ca2+ uptake by mitochondria and exposure of the mitochondria to oxygen free radicals may explain the enhanced cellular injury observed during post-ischemic reperfusion.

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PubMed1985

A phosphorus-31 nuclear magnetic resonance study of effects of altered thyroid state on cardiac bioenergetics.

We have used 31P nuclear magnetic resonance (NMR) techniques to characterize bioenergetic changes in the Langendorff-perfused rat heart accompanying alterations in thyroid state. Cytosolic phosphocreatine and inorganic phosphate concentrations changed significantly in both the hypo- and hyperthyroid groups compared to controls; the calculated phosphorylation potential [( ATP]/[ADP][Pi]) increased by 60% in hypothyroidism and decreased by 60% in hyperthyroidism relative to the euthyroid value of 47 X 10(3) M-1. Creatine phosphokinase (CPK) and mitochondrial ATP synthase rates were measured in the intact tissue using a saturation-transfer NMR method. There were no significant differences in the measured fluxes through the CPK reaction among the three groups (4.24 +/- 1.00 mM X sec-1 for the euthyroid group). Although O2 consumption increased by 46% in hearts from hyperthyroid animals, no change in the measured mitochondrial ATP synthase flux was observed compared to the euthyroid flux of 1.05 +/- 0.11 mM X sec-1. These results suggest that the apparent in situ P/O ratio of mitochondria in hearts from hyperthyroid animals is reduced relative to that in euthyroid controls.

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PubMed1986

A portrait of the adenosine triphosphate synthetase-hydrolase.

It is proposed that the ATP-synthetic and ATP-hydrolytic activities of energy-transducing mitochondria, chloroplasts and bacterial membranes are due to different enzyme systems. It is suggested that the alpha-subunits of the oligomycin-sensitive coupling factor catalyze synthesis and the beta-subunits catalyze hydrolysis. Evidence is assembled from the literature in support of this concept.

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PubMed1983

Non-random patterns of nucleotide substitutions and codon strategy in the mammalian mitochondrial genes coding for identified and unidentified reading frames.

The base sequence of large part of the mitochondrial DNA of Wistar rats is presented. The sequence is compared with those of other mammalian mitochondrial DNAs. The nucleotide and amino acid homologies, codon strategy, nature and patterns of substitutions are reported. It results a very high amount of silent substitutions and, in short divergence time, a predominance of transitions on transversions. In both types of substitutions a strong bias in avoiding the use of the G in the third codon position is observed.

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PubMedDate not supplied

[Effect of visible light on the ATP synthetase function of mitochondria].

Dependence of oxidative phosphorylation in rat liver mitochondria on redox state of endogenous flavoenzymes was studied. Regulation of the redox state of endogenous flavins in mitochondria was performed by visible light illumination of lambda = 380 nm in oxygen free as well as in oxygenated media. A decrease of oxidative phosphorylation was obtained at full reduction of flavins (respiratory control and ATP synthesis were measured); this effect was partially recovered when flavin was reoxidized by oxygen. Results of ESR measurements of the signal gl = 2.00 associated with semireduced flavins were in accordance with the appearance of diamagnetically completely reduced form of flavin. These facts may be considered as evidence of the regulative role of flavins in oxidative phosphorylation.

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PubMedDate not supplied

[Detection of a paramagnetic product developing during oxidative phosphorylation in mitochondria].

It was shown by ESR technique using flow system combined with ESR-spectrometer that paramagnetic product appearing in the course of oxidative phosphorylation was directly associated with mitochondrial ATPase operation. A decrease of ESR signal intensity and the changes of its form observed on mitochondria uncoupled by 2,4-dinitrophenol as compared with those inhibited by olygomicin suggest that in the case of olygomycin block a free radical ATPase linked intermediate can be recorded, the ESR signal of which seems to be partly due to flavin semiquinone of ATPsynthetase itself.

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PubMed1982

[ATP-synthetase activity, respiration and cytochromes of rat heart mitochondria in aging and hyperthyroidism].

The ATP-synthetase activity, the rate of oxygen uptake under different metabolic conditions, the tightness of coupling of respiration to oxidative phosphorylation and the cytochrome contents in heart mitochondria of rats from different age groups were studied under normal conditions and in hyperthyroidism. It was found that heart mitochondria of aged animals did not practically differ in terms of their functional activity from those of the young animals. Administration of thyroxin to the animals from all age groups produced no significant effects on the state of mitochondria, increasing the rate of ATP synthesis on alpha-glycerophosphate, which was especially well-pronounced in aged animals, and the cytochrome content in 1-month-old rats.

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PubMed1982

[Effect of freezing-thawing rates on the functional state and ionic permeability of rat liver mitochondria].

The effects of various rats of freezing-thawing reactions on the functional state and ionic permeability of rat liver mitochondria were studied. The degree of mitochondrial damage during the freezing -- thawing process depended on the rate of thawing rather than on that of freezing. The mitochondria which were slowly or rapidly frozen down to --196 degrees and subsequently slowly thawed revealed a higher membrane permeability for K+ Na+ and H+ and a more than 2-fold increase of the ATPase activity and the maximal rate of NADH oxidation via the antimycin-insensitive pathway in the presence of cytochrome c. This was concomitant with a complete inhibition of the ATP-synthetase activity and a marked inhibition of the respiratory chain function due to the efflux of cytochrome c from the inner mitochondrial membrane. After freezing and rapid thawing the functional activity of mitochondria changed insignificantly. A comparison of different cryoeffects demonstrated that the minimal damaging effects were exerted by rapid freezing -- rapid thawing, when the mitochondria partly restored their ability for oxidative phosphorylation.

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PubMed1983

Labeling of subunit b of the ATP synthase from Escherichia coli with a photoreactive phospholipid analogue.

Purified ATP synthase (F1F0) from Escherichia coli K12 was labeled with the hydrophobic photoreactive label 1-palmitoyl 2-(2-azido-4-nitro)benzoyl sn-glycero-3-[3H]phosphocholine in reconstituted proteoliposomes. The F0-subunit b was predominantly labeled. A very low amount of label was detected on the other F0-subunits a and c. The label in subunit b could be traced back by proteolytic digestion to the NH2-terminal fragment 1 to 53 which contains the stretch of hydrophobic amino acid residues 1 to 32. By sequencing the intact protein, the distribution of label among the amino acids in this segment was determined. Cysteine 21 was predominantly labeled. Other labeled amino acids occurred at the NH2-terminal (Asn-2) and at position 26 (tryptophan). Due to the restricted mobility of the label in the lipid bilayer, these residues are suggested to be located in or close to the polar head of the lipid bilayer. These results will be compared with predictions for the arrangement of the polypeptide b derived from the hydrophobicity profile.

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PubMed1983

Probes of catalytic site cooperativity during catalysis by the chloroplast adenosine triphosphate and the adenosine triphosphate synthase.

During net nucleoside triphosphate synthesis by chloroplast ATP synthase the extent of water oxygen incorporation into each nucleoside triphosphate released increases with decrease in ADP, GDP or IDP concentration. Likewise, during net ATP hydrolysis by the Mg2+-activated chloroplast ATPase, the extent of water oxygen incorporation into each Pi released increases as the ATP, GTP, or ITP concentration is decreased. However, the concentration ranges in which substrate modulation occurs differs with each nucleotide. Modulation of oxygen exchange during synthesis and hydrolysis of adenine nucleotides, as measured by variation in the extent of water oxygen incorporation into products, occurs below 250 microM. In contrast, guanosine and inosine nucleotides alter the extent of exchange at higher and much wider concentration ranges. Activation of the chloroplast ATPase by either heat or trypsin results in similar catalytic behavior as monitored by ATP modulation of oxygen exchanges during hydrolysis in the presence of Mg2+. More exchange capacity is evident with octylglucoside-activated enzyme at all ATP concentrations. High levels of tentoxin were also found to alter the catalytic exchange parameters resulting in continued water oxygen exchange into Pi released during hydrolysis at high ATP concentrations. Little or no oxygen exchange accompanies ATP hydrolysis in the presence of Ca2+. The [18O]Pi species formed from highly gamma-18O-labeled ATP at lower ATP concentrations gives a distribution as expected if only one catalytic pathway is operative at a given ATP concentration. This and other results support the concept of catalytic cooperativity between alternating sites as explanation for the modulation of oxygen exchange by nucleotide concentration.

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PubMed1982

The membrane bound ATP synthase of Escherichia coli: a review of structural and functional analyses of the atp operon.

The structure of the atp operon, which contains the genes for the eight subunits alpha, beta, gamma, delta, epsilon, a, b and c of the membrane bound ATP synthase of Escherichia coli as determined by genetic experiments and DNA sequencing, is reviewed. The localization of transcription signals, namely of one major and two minor promoters, as well as the determination of the stoichiometry of the subunits (alpha:beta:gamma:delta:epsilon:a:b:c = 3:3:1:1:1:1:2:12-15) is summarized.

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