ATP Synthesis System Research Articles

Emerging mutant populations of Listeria monocytogenes EGD-e under selective pressure of Thymbra capitata essential oil question its use in food preservation

Due to their excellent antimicrobial properties, essential oils (EO) have been proposed as potential preservatives for certain kinds of foods, such as dairy products. However, the occurrence of pathogenic populations that are resistant to EOs could pose a health risk. This report seeks to assess the emergence of resistant populations in Listeria monocytogenes EGD-e growth at 37 °C under selective pressure of Thymbra capitata EO (TCO), to characterise their resistance in laboratory media, and to identify their genotypic changes, as well as to evaluate the resistance in skimmed milk. TCO cyclic treatment allowed the isolation of two L. monocytogenes EGD-e resistant strains against the EO: LmSTCO by sublethal doses (75 µL/L TCO) and LmLTCO by lethal doses (300 µL/L TCO) after 20 and 30 cycles, respectively. Both strains displayed an increase of the minimum inhibitory and bactericidal concentration against TCO and a higher survival rate after lethal treatments than the wild-type strain (LmWT). Growth kinetics revealed a better adaptation of LmSTCO in presence of TCO, while LmLTCO grew more slowly compared to LmWT, even in the absence of the antimicrobial. Moreover, a slight increase in cross-resistance to antibiotics was observed: LmSTCO to β-lactams and LmLTCO to a series of broad-spectrum antibiotics. The genomic study revealed one sole nucleotide change in LmSTCO located in plsC gene codifying an enzyme involved in the production of phosphatidic acid, a precursor in cell membrane synthesis. Five genetic variations were found in LmLTCO: among them, the deletion of an ATP-synthesis system involved in slowing bacterial growth. Inhibition and inactivation assays in skimmed milk confirmed the increased resistance of both strains, thereby indicating a safety risk in case these strains emerge in the food chain. These results strongly suggest that the occurrence of such resistances should be taken into account in order to ensure the efficacy of natural antimicrobials in the design of food preservation strategies.

On Local Coupling of Electron Transport and ATP-Synthesis System in Mitochondria. Theory and Experiment.

A brief description of the principal directions for searching and investigating the model of local coupling between respiration and phosphorylation proposed by R. Williams is given in this paper. We found conditions where it was possible to reveal typical functional special features of the mitochondrial phosphorylating system. According to the theory, such special features should be observed experimentally if the mitochondrial phosphorylating system operated in the state of a supercomplex. It was proved that the phosphorylating system is able to operate in two states: P. Mitchell state and R. Williams state. It was demonstrated that in the ATP synthesis reaction, ATP-synthase (F1F0) was able to use thermodynamic potential of Bronsted acids as a source of energy. It was shown using a double-inhibitor titration technique that when the phosphorylating system operated in the supercomplex state, the electron transfer system and ATP-synthesis system were docked rigidly. A model system of chemical synthesis of membrane-bound proton fraction (Bronsted acids), carrying a free energy excess, was developed on the model of bilayer lipid membrane. Catalysts selectively accelerating proton detachment of this fraction were also found. The formation of a Bronsted acids fraction carrying free energy excess was recorded during the operation of proton pumps on mitochondrial and mitoplastic membranes. In the experimental part of the work, a brief description is given of studies on new uncouplers that transfer the phosphorylation system from the local coupling state to the state of transmembrane proton transfer. Thus, they accelerated the respiration of mitochondria and decreased the ADP/O parameter.

Respiration chain and ATP-synthesis system function as tightly-bounded supercomplex

Respiration chain and ATP-synthesis system function as tightly-bounded supercomplex

Role of estrogen on skeletal muscle mitochondrial function in ovariectomized rats: a time course study in different fiber types

Postmenopausal women are prone to develop obesity and insulin resistance, which might be related to skeletal muscle mitochondrial dysfunction. In a rat model of ovariectomy (OVX), skeletal muscle mitochondrial function was examined at short- and long-term periods after castration. Mitochondrial parameters in the soleus and white gastrocnemius muscle fibers were analyzed. Three weeks after surgery, there were no differences in coupled mitochondrial respiration (ATP synthesis) with pyruvate, malate, and succinate; proton leak respiration; or mitochondrial reactive oxygen species production. However, after 3 wk of OVX, the soleus and white gastrocnemius muscles of the OVX animals showed a lower use of palmitoyl-carnitine and glycerol-phosphate substrates, respectively, and decreased peroxisome proliferator-activated receptor-γ coactivator-1α expression. Estrogen replacement reverted all of these phenotypes. Eight weeks after OVX, ATP synthesis was lower in the soleus and white gastrocnemius muscles of the OVX animals than in the sham-operated and estrogen-treated animals; however, when normalized by citrate synthase activity, these differences disappeared, indicating a lower muscle mitochondria content. No differences were observed in the proton leak parameter. Mitochondrial alterations did not impair the treadmill exercise capacity of the OVX animals. However, blood lactate levels in the OVX animals were higher after the physical test, indicating a compensatory extramitochondrial ATP synthesis system, but this phenotype was reverted by estrogen replacement. These results suggest early mitochondrial dysfunction related to lipid substrate use, which could be associated with the development of the overweight phenotype of ovariectomized animals.

Ureaplasma Urease Genes have Undergone a Unique Evolutionary Process

Ureaplasma, a member of mycoplasmas, has a unique ATP synthesis system, which is coupled to the urea hy- drolysis. Urease catalyzes the hydrolysis of urea into carbon dioxide and ammonia. Phylogenetic analyses of the urease genes indicated that Ureaplasma urease genes were not gained by recent horizontal transfer and have a unique evolution- ary process. Ureaplasma unique ATP synthesis system leaded to breakdown of the glycolysis pathway. Some glycolytic genes are absent and some glycolytic genes are evolving under relaxed selection in Ureaplasma. Probably glycolytic genes can be used as an indicator of ATP synthesis system. Thus, the organisms that have incomplete glycolysis pathway or glycolytic genes evolving under relaxed selection would have an ATP synthesis system independently of the glycolysis. Mycoplasmas are widespread in nature as parasites of mammals, reptiles, fishes, arthropods, and plants (1). During the mycoplasma evolution, gene loss has occurred fre- quently, resulting in very small genome size (1-3). The re- ductive evolution of mycoplasmas is still in progress. The genus Ureaplasma is a member of mycoplasmas, which gen- erates 95% of its ATP using the hydrolysis of urea (4). Growth of Ureaplasma is dependent on urea (5). This unique ATP synthesis is not found in the other mycoplasmas. In fact, key enzymes in the glycolytic pathway are absent in Ureaplasma (6). In addition, some glycolytic genes of Urea- plasma are evolving under relaxed selection (7, 8). Thus, the glycolysis pathway is collapsing in Ureaplasma.

Effects of nitrosopropofol on mitochondrial energy-converting system

Nitrosopropofol (NOPR) is a relatively stable compound obtained from the reaction between the general anesthetic 2,6 diisopropylphenol (propofol) and nitrosoglutathione (GSNO) and bearing a more acidic phenol group than propofol. It interfered with mitochondrial energetic metabolism in a concentration-dependent manner. Concentrations as high as 100 or 200 μM disrupted both oxidative phosphorylation and electron transport. Low concentrations of NOPR (50 μM) markedly slowed down the electron transport rate which was insensitive both to ADP and uncoupler stimulation and spontaneously gradually stopped. Consequently, both the transmembrane potential production and the ATP synthesis system were affected. In the presence of 10 or 20 μM NOPR, mitochondria respired but showed a worsening of the respiratory control and produced a transmembrane potential useful to respond to a phosphorylation pulse, but were not able to restore it. These results were consistent with ATP synthesis and swelling experiments. NOPR was effective at concentrations lower than those required by the combination of propofol and GSNO, suggesting that mitochondria might be able to catalyze the reaction between GSNO and propofol and that the resulting metabolite was more active on mitochondrial membrane structure than the parent compounds. Although the details of the process are yet unknown, the mechanism presented may be of potential relevance to rationalize the pathophysiological effects of propofol.

Mechanism of somatic mitochondrial DNA mutations associated with age and diseases

Mitochondrial DNA (mtDNA) that codes protein subunits essential for the maintenace of mitochondrial ATP synthesis system acquires mutations at a much higher rate than that in nuclear DNA. Recent study has revealed that somatically acquired mutations such as deletions in mtDNA are caused mainly by oxygen free-radical damage. Cumulative accumulation of these somatic mutations during the life of an individual causes bioenergetic deficit leading to cell death and normal ageing. The base-sequencing of the entire mtDNA from 48 individuals revealed that germ-line point mutations accelerate extensively the somatic oxygen free-radical damage and the deletions leading to generation of more than a hundred kinds of mtDNA minicircle. These accelerated somatic mutations are expressed as premature ageing of the patients with degenerative diseases. Comprehensive analyses of the entire mtDNA, including the total base-sequencing and the total deletion correlating with oxygen free-radical damage, has revealed a clear relationship between the genotype and its phenotype, such as the severity of clinical symptoms and the survival time of the patients. Extensive generation of mtDNA minicircles caused by the oxygen free radical implies a close relation between the redox mechanism of ageing and the programmed cell-death machinery.

Control of oxidative phosphorylation in rat muscle mitochondria: implications for mitochondrial myopathies

The control of oxidative phosphorylation has been studied in normal skeletal muscle isolated from the hind legs of rats. The control coefficients of different steps of oxidative phosphorylation on the flux of O 2 consumption were determined by the inhibitor method and calculation was done according to the model of Gellerich et al. (FEBS Lett. 274 (1990) 167–170) using a non-linear regression fitting procedure. The respiration was recorded with pyruvate (+malate) and palmitoyl- l-carnitine (+malate) as respiratory substrates, which are the main substrates oxidized in the muscle. It appears that the control is broadly distributed among the different complexes of the respiratory chain, and of the ATP synthesis system. Our results also provide an explanation for the threshold effects often evidenced in the clinical manifestation of mitochondrial diseases.

The effects of demethylsterigmatocystin and sterigmatin on ATP synthesis system in mitochondria: A comparison with sterigmatocystin

The effects of demethylsterigmatocystin and its structural isomer, sterigmatin, on oxidative phosphorylation of mitochondria were studied by means of isolated rat liver mitochondria in comparison with sterigmatocystin. Both compounds were found to uncouple the oxidative phosphorylation in mitochondria, causing marked decreases in RC index and P/O ratio. Sterigmatin, in which dihydrobisfuran ring and xanthone nucleus are combined in a linear manner, was evidently more toxic to mitochondrial functions than demethylsterigmatocystin which was an angular molecular shape. Though their uncoupling concentrations were rather high for assessing theirin vivo toxicity, a good correspond was observed between their orders of potencies in the toxicity to mitochondrial functions and in the cytotoxicity to rat hepatocytes. The demethylation of sterigmatocystin resulted in an obvious decrease of uncoupling activity.

Inhibitory effect of sterigmatocystin and 5,6-dimethoxysterigmatocystin on ATP synthesis in mitochondria.

The inhibitory effects of sterigmatocystin, O-methylsterigmatocystin, and 5,6-dimethoxysterigmatocystin on the ATP synthesis system in mitochondria were compared with that of aflatoxin B1, which disturbs the respiratory chain in mitochondria. Sterigmatocystin and 5,6-dimethoxysterigmatocystin were found to uncouple the oxidative phosphorylation process without causing depression of state 3 respiration. O-Methylsterigmatocystin did not exhibit uncoupling activity at the limited concentrations tested (due to its low solubility in an aqueous system). These compounds, as well as aflatoxin B1, elicited neither pseudo-energized nor energized swelling of mitochondria and did not inhibit Ca2+-induced swelling of mitochondria.