Aerobic Respiratory Pathways Research Articles

Efficient starvation therapy with three-pathway blocking in combination with PTT/CDT for TME reversal and tumor apoptosis

Single cancer starvation therapy (ST) strategy can’t achieve satisfactory anti-tumor effect, mainly due to the diversified nutritional sources of tumor cells. Herein, CuS@Axitinib-SiO2@2-Deoxy-D-glucose(2-DG)-CaCO3-RGD nanoparticles (CADCR NPs) were prepared for three-pathway blocking for efficient starvation therapy as well as reinforced photothermal therapy (PTT) and chemodynamic therapy (CDT). After CADCR NPs were targeted to tumor cells, CaCO3 was ruptured in the acidic environment, releasing Ca2+ to chelate glutamine and cutting off the glutamine metabolic pathway of the tumor. 2-DG was also released from mesoporous SiO2 and restrained the glycolytic pathway of tumor cells. In addition, under the thermal stimulus of near-infrared irradiation, axitinib was released from CuS NPs, which inhibited the proliferation of tumor blood vessels, ultimately inhibiting the aerobic respiratory pathway of tumor cells. Interestingly, CADCR NPs also showed potential to reshape the tumor microenvironment (TME) and promoted the transformation of macrophages from M2 to M1 type, increasing the expression of CD8+ T cells in the tumor site. In conclusion, CADCR NPs achieve severe tumor starvation by simultaneously interfering with three energy metabolic pathways, and further enhance tumor treatment with the aid of PTT, CDT, and TME improvement, which exhibits great potential for clinical cancer therapy.

Effect of Hypoxia on Photosystem II of Tropical Seagrass Enhalus acoroides in the Dark.

Hypoxia induced by eutrophication has become an important factor threatening the survival of coastal life such as Enhalus acoroides. The purpose of the current study was to explore the effect of hypoxia on photosystem II (PSII) of E. acoroides in the dark. The results showed that long-term dark hypoxia damages PSII activity of E. acoroides. The lower the oxygen content and the longer the hypoxic duration, the more seriously PSII was damaged and the less light-independent recovery parts of the damaged PSII. The damage to PSII caused by hypoxia was unrelated to ROS but related to respiration, because the respiration rate decreased with the decrease of oxygen content and PSII activity decreased significantly even at a normal oxygen content after the inhibition of aerobic respiratory pathway. Hypoxia reduced energy fluxes between the antennas and the RCs, and generated many inactive RCs, which significantly reduced the electron transfer efficiency of PSII. Severe hypoxia (2.65 mg L-1 oxygen content) caused chlorophyll degradation. The study demonstrated that hypoxia damages PSII of E. acoroides and inhibits PSII recovery in the dark. We suggested that hypoxia together with other environment stressors would be the key reason for the decline of E. acoroides meadows.

Alternative Oxidase Activity Reduces Stress in Vibrio fischeri Cells Exposed to Nitric Oxide.

Alternative oxidase (Aox) is a non-energy-conserving respiratory oxidase found in certain eukaryotes and bacteria, whose role in physiology is not entirely clear. Using the genetically tractable bacterium Vibrio fischeri as a model organism, I have identified a role for Aox to reduce levels of stress in cells exposed to oxygen and nitric oxide (NO). In V. fischeri lacking the NO-detoxifying enzyme flavohemoglobin (Hmp), deletion of aox in cells grown in the presence of oxygen and NO results in alterations to the transcriptome that include increases in transcripts mapping to stress-related genes. Using fluorescence-based reporters, I identified corresponding increases in intracellular reactive oxygen species and decreases in membrane integrity in cells lacking aox Under these growth conditions, activity of Aox is linked to a decrease in NADH levels, indicating coupling of Aox activity with NADH dehydrogenase activity. Taken together, these results suggest that Aox functions to indirectly limit production of ferrous iron and damaging hydroxyl radicals, effectively reducing cellular stress during NO exposure.IMPORTANCE Unlike typical respiratory oxidases, alternative oxidase (Aox) does not directly contribute to energy conservation, and its activity would presumably reduce the efficiency of respiration and associated ATP production. Aox has been identified in certain bacteria, a majority of which are marine associated. The presence of Aox in these bacteria poses the interesting question of how Aox function benefits bacterial growth and survival in the ocean. Using the genetically tractable marine bacterium Vibrio fischeri, I have identified a role for Aox in reduction of stress under conditions where electron flux through the aerobic respiratory pathway is inhibited. These results suggest that Aox activity could positively impact longer-term bacterial fitness and survival under stressful environmental conditions.

The Global Redox Responding RegB/RegA Signal Transduction System Regulates the Genes Involved in Ferrous Iron and Inorganic Sulfur Compound Oxidation of the Acidophilic Acidithiobacillus ferrooxidans.

The chemical attack of ore by ferric iron and/or sulfuric acid releases valuable metals. The products of these reactions are recycled by iron and sulfur oxidizing microorganisms. These acidophilic chemolithotrophic prokaryotes, among which Acidithiobacillus ferrooxidans, grow at the expense of the energy released from the oxidation of ferrous iron and/or inorganic sulfur compounds (ISCs). In At. ferrooxidans, it has been shown that the expression of the genes encoding the proteins involved in these respiratory pathways is dependent on the electron donor and that the genes involved in iron oxidation are expressed before those responsible for ISCs oxidation when both iron and sulfur are present. Since the redox potential increases during iron oxidation but remains stable during sulfur oxidation, we have put forward the hypothesis that the global redox responding two components system RegB/RegA is involved in this regulation. To understand the mechanism of this system and its role in the regulation of the aerobic respiratory pathways in At. ferrooxidans, the binding of different forms of RegA (DNA binding domain, wild-type, unphosphorylated and phosphorylated-like forms of RegA) on the regulatory region of different genes/operons involved in ferrous iron and ISC oxidation has been analyzed. We have shown that the four RegA forms are able to bind specifically the upstream region of these genes. Interestingly, the phosphorylation of RegA did not change its affinity for its cognate DNA. The transcriptional start site of these genes/operons has been determined. In most cases, the RegA binding site(s) was (were) located upstream from the −35 (or −24) box suggesting that RegA does not interfere with the RNA polymerase binding. Based on the results presented in this report, the role of the RegB/RegA system in the regulation of the ferrous iron and ISC oxidation pathways in At. ferrooxidans is discussed.

A Biochemical Approach to Study the Role of the Terminal Oxidases in Aerobic Respiration in Shewanella oneidensis MR-1

The genome of the facultative anaerobic γ-proteobacterium Shewanella oneidensis MR-1 encodes for three terminal oxidases: a bd-type quinol oxidase and two heme-copper oxidases, a A-type cytochrome c oxidase and a cbb 3-type oxidase. In this study, we used a biochemical approach and directly measured oxidase activities coupled to mass-spectrometry analysis to investigate the physiological role of the three terminal oxidases under aerobic and microaerobic conditions. Our data revealed that the cbb 3-type oxidase is the major terminal oxidase under aerobic conditions while both cbb 3-type and bd-type oxidases are involved in respiration at low-O2 tensions. On the contrary, the low O2-affinity A-type cytochrome c oxidase was not detected in our experimental conditions even under aerobic conditions and would therefore not be required for aerobic respiration in S. oneidensis MR-1. In addition, the deduced amino acid sequence suggests that the A-type cytochrome c oxidase is a ccaa 3-type oxidase since an uncommon extra-C terminal domain contains two c-type heme binding motifs. The particularity of the aerobic respiratory pathway and the physiological implication of the presence of a ccaa 3-type oxidase in S. oneidensis MR-1 are discussed.

The bio-energetic theory of carcinogenesis

The altered energy metabolism of tumor cells provides a viable target for a non toxic chemotherapeutic approach. An increased glucose consumption rate has been observed in malignant cells. Warburg (Nobel Laureate in medicine) postulated that the respiratory process of malignant cells was impaired and that the transformation of a normal cell to malignant was due to defects in the aerobic respiratory pathways. Szent-Györgyi (Nobel Laureate in medicine) also viewed cancer as originating from insufficient availability of oxygen. Oxygen by itself has an inhibitory action on malignant cell proliferation by interfering with anaerobic respiration (fermentation and lactic acid production). Interestingly, during cell differentiation (where cell energy level is high) there is an increased cellular production of oxidants that appear to provide one type of physiological stimulation for changes in gene expression that may lead to a terminal differentiated state. The failure to maintain high ATP production (high cell energy levels) may be a consequence of inactivation of key enzymes, especially those related to the Krebs cycle and the electron transport system. A distorted mitochondrial function (transmembrane potential) may result. This aspect could be suggestive of an important mitochondrial involvement in the carcinogenic process in addition to presenting it as a possible therapeutic target for cancer. Intermediate metabolic correction of the mitochondria is postulated as a possible non-toxic therapeutic approach for cancer.

Bacterial Iron–Sulfur Regulatory Proteins As Biological Sensor-Switches

In recent years, bacterial iron-sulfur cluster proteins that function as regulators of gene transcription have emerged as a major new group. In all cases, the cluster acts as a sensor of the environment and enables the organism to adapt to the prevailing conditions. This can range from mounting a response to oxidative or nitrosative stress to switching between anaerobic and aerobic respiratory pathways. The sensitivity of these ancient cofactors to small molecule reactive oxygen and nitrogen species, in particular, makes them ideally suited to function as sensors. An important challenge is to obtain mechanistic and structural information about how these regulators function and, in particular, how the chemistry occurring at the cluster drives the subsequent regulatory response. For several regulators, including FNR, SoxR, NsrR, IscR, and Wbl proteins, major advances in understanding have been gained recently and these are reviewed here. A common theme emerging from these studies is that the sensitivity and specificity of the cluster of each regulatory protein must be exquisitely controlled by the protein environment of the cluster. A major future challenge is to determine, for a range of regulators, the key factors for achieving control of sensitivity/specificity. Such information will lead, eventually, to a system understanding of stress response, which often involves more than one regulator.

The effects of mutation of the anr gene on the aerobic respiratory chain of Pseudomonas aeruginosa.

The anr gene of Pseudomonas aeruginosa encodes a transcriptional regulator of anaerobic gene expression, homologous to the Fnr protein of Escherichia coli. We report here that Anr has a role in regulating the activity of the aerobic respiratory chain of P. aeruginosa. Strains with internal deletions in their anr gene had lowered levels of membrane bound cytochromes whilst the activity of the cytochrome c oxidase, cytochrome co (likely to be a cytochrome cbb3-type oxidase), and the cyanide-insensitive respiratory pathway was markedly higher than in the wild-type strains. These data, and the finding that provision of multiple copies of the anr gene led to severe repression of these respiratory activities, suggest that Anr is a repressor of aerobic respiratory pathways and possibly the terminal oxidases themselves. In contrast, Anr activated cytochrome c peroxidase, a respiratory chain linked enzyme induced under low oxygen conditions.

The effects of mutation of the anr gene on the aerobic respiratory chain of Pseudomonas aeruginosa

The anr gene of Pseudomonas aeruginosa encodes a transcriptional regulator of anaerobic gene expression, homologous to the Fnr protein of Escherichia coli. We report here that Anr has a role in regulating the activity of the aerobic respiratory chain of P. aeruginosa. Strains with internal deletions in their anr gene had lowered levels of membrane bound cytochromes whilst the activity of the cytochrome c oxidase, cytochrome co (likely to be a cytochrome cbb 3-type oxidase), and the cyanide-insensitive respiratory pathway was markedly higher than in the wild-type strains. These data, and the finding that provision of multiple copies of the anr gene led to severe repression of these respiratory activities, suggest that Anr is a repressor of aerobic respiratory pathways and possibly the terminal oxidases themselves. In contrast, Anr activated cytochrome c peroxidase, a respiratory chain linked enzyme induced under low oxygen conditions.

O 2 consumption in the in-vitro fetal side human placenta

The relative dependence of placental O 2 consumption (Ṁ O 2 on O 2 supply (SupO 2) parameters, and the fraction of aerobic O 2 utilization, was studied by in-vitro perfusion of the fetal side of term human placental lobes. Placental Ṁ O 2 was a function of the combined effect of SupO 2 parameters (P O 2 , perfusate flow rate, perfusate effective O 2 solubility) and not of each separately. At SupO 2 greater than 800 μl/(min · lobe), Ṁ O 2 saturated at 260 μl/(min · lobe). No accumulation of O 2 debt could be detected even after 2 h anoxia. Adding CN − or CO to perfusate did not abolish Ṁ O 2 , and a residual Ṁ O 2 of 31–37% of control Ṁ O 2 was measured. In its Ṁ O 2 placenta is a typical conformer tissue. This conformity enables conservation of O 2 transfer to the embryo even when placental SupO 2 is radically reduced. Only about 60–70% of placental Ṁ O 2 is utilized in the aerobic respiratory pathway, while about 30–40% of the oxygen is used in other pathways.

Entamoeba histolytica: a eukaryote without glutathione metabolism.

Entamoeba histolytica was found to grow normally without producing glutathione and the main enzymes of glutathione metabolism, indicating that glutathione is not essential for many eukaryotic processes. This parasitic amoeba is an unusual eukaryote whose special features may help define the crucial functions of glutathione in those eukaryotes that do use it. Since Entamoeba histolytica lacks mitochondria and the usual aerobic respiratory pathways, the finding that it grows without glutathione and other evidence support the hypothesis that a primary function of glutathione in eukaryotes involves protection against oxygen toxicity associated with mitochondria and suggest that eukaryotes may have acquired glutathione metabolism at the time that they acquired mitochondria.

Nematoda: Aerobic respiratory pathways of adult parasitic species

Aerobic respiratory pathways have been compared in adult parasitic nematodes, including Trichostrongylus colubriformis, Nippostrongylus brasiliensis, Ostertagia ostertagi, Cooperia oncophora, Haemonchus contortus, Oesophagostomum venulosum, Chabertia ovina, Dictyocaulus filaria, Dictyocaulus viviparus, and Ascaridia galli. Respiration was measured in both whole worm or tissue homogenates and isolated mitochondrial fractions, and delineated into the mammalian type or alternative respiratory pathways on the basis of their inhibition by antimycin A. The alternative, antimycin A-insensitive respiratory pathway was of comparable activity in all parasitic nematodes studied, irrespective of the body diameter or habitat of the worm. The mammalian-type, antimycin A-sensitive respiratory pathway showed variations; the extent of this pathway correlated with both the body diameter and habitat of the worm, being greater in thinner worms and those worms whose habitat is supposedly more aerobic.

Cytochromes of the trimethylamine N-oxide anaerobic respiratory pathway of Escherichia coli

Escherichia coli grown anaerobically with trimethylamine N-oxide (TMAO) as a terminal electron acceptor develops a new cytochrome pathway in addition to the aerobic respiratory pathways which are still formed. Formate, NADH, and possibly other substrates derived from glucose, supply electrons to this pathway. Cytochromes with α-absorption peaks at about 548, 552, 554 and 557 nm are rapidly reoxidized by TMAO in a reaction which is not inhibited by 2- n-heptyl-4-hydroxyquinone N-oxide. CuSO 4 inhibits the reoxidation by TMAO of the first two of these cytochromes. This suggests that the pathway of electron transfer leading to the reduction of TMAO is: substrates → cytochromes 548,552 → cytochromes 554,557 → trimethylamine- N-oxide reductase → TMAO. These cytochromes, but not those of the aerobic respiratory pathways, are reoxidized by the membrane-impermeant oxidant ammonium persulfate in intact cells. This suggests that the cytochromes of the TMAO reduction pathway and / or trimethylamine- N-oxide reductase are situated at the periplasmic surface of the cytoplasmic membrane of E. coli.

Nippostrongylus brasiliensis and Ascaridia galli: Mitochondrial respiration in free-living and parasitic stages

Aerobic respiratory pathways have been delineated and respiratory efficiency has been assessed in mitochondria isolated from embryonated eggs, infective larvae, and adult Nippostrongylus brasiliensis and Ascaridia galli. Mitochondrial respiration in free-living stages of N. brasiliensis is mediated mainly by a mammalian-like antimycin A- and cyanide-sensitive pathway; specific respiratory activity is high and oxidative phosphorylation efficient. In mitochondria of adult N. brasiliensis, antimycin A- and cyanide-sensitive respiration is decreased relative to respiration though an alternative pathway, and specific respiratory activity and mitochondrial efficiency are lower. Respiration in mitochondria from embryonated eggs and tissues of adult A. galli is comparable, and apparently mediated by an antimycin A- and cyanide-insensitive alternative respiratory pathway; no evidence for the presence of a mammalian-like respiratory pathway in embryonated eggs of A. galli was found. The results of this study are compared to mitochondrial respiration in eggs, larvae, and adult body wall muscle of Ascaris suum.

Stimulation of pinocytosis in the macrophage by lymphocyte mediators: II. Evidence that the stimulating factor is MAF, and studies on the cellular requirements for response to the mediator

Partial characterization of a lymphocyte-derived mediator which stimulates macrophage pinocytosis of horseradish peroxidase is described. The mediator elutes with Sephadex G-100 fractions ranging from 25,000–68,000 molecular weight. It is neuraminidase sensitive and has a buoyant density characteristic of glycoproteins. These properties are identical with those of migration inhibitory factor and macrophage-activating factor, suggesting that they may be the same material. Using a variety of inhibitors, certain cellular and metabolic functions of the mediator-induced stimulatory process were investigated. Anaerobic glycolysis is critical to any stimulation, whereas submaximal stimulation can occur in the absence of an intact aerobic respiratory pathway. Protein synthesis is required for stimulation of pinocytosis. However, neither microtubule nor microfilament function appears necessary for the mediator to induce a stimulatory response as assessed by enhancement of pinocytosis.

Comment of Egami's concept of the evolution of nitrate respiration.

Recent results suggest that the presence of common nitrogen salts (sodium nitrite and nitrate) in the irradiation medium can markedly protect filamentous blue green algae from potentially lethal ultraviolet light irradiation. Our results as well as general biologica-l arguments as presented by Egami (above) support and extend Egami's original view that anaerobic respiratory pathways using nitrite and nitrate as terminal electron acceptors evolved prior to oxygen requiring aerobic respiratory pathways.

Anaerobic Respiration in the Dormancy of Rice Seed

We investigated the effects of high temperature treatment (40°C three weeks) on dormant rice seeds of Hadsaduri (Oryza sativa cv.) which was known as a variety of deep dormancy and results obtained are summarized as follows; 1. The seed of which dormancy was broken by high temperature treatment could germinate under both aerobic and anaerobic conditions, whereas dormant seed could not germinate under the anaerobic condition. 2. Warburg manometric techniques were used for the determination of respiratory gas exchange. In the case of non-dormant seeds, the amount of released carbon dioxide always exceeded that of oxygen uptake. Whereas the dormant seeds showed nearly the same amount of oxygen uptake and carbon dioxide release. 3. Determination of ethyl alcohol was carried out by gas chromatography. Non-dormant seeds usually produced more amount of ethyl alcohol than dormant seeds. When both dormant and non-dormant seeds were incubated under nitrogen gas at 30°C, the same tendency as above was observed. 4. When non-dormant seeds were co-treated with sodium iodoacetate, which was known as one of the inhibitors of enzyme SH group, at 5mM and 10mM concentrations, the production of ethyl alcohol was inhibited. Germination of hulled rice of non-dormant seeds was not affected up to the concentraton to 10mM under aerobic condition, but almost completely inhibited at 5mM under submerged condition. From the facts described above, it might be possible to consider that the dormant rice seed had the aerobic respiratory pathway but had not an active anaerobic respiratory pathway sufficient for germination. Effects of high temperature treatment on breaking the dormancy of rice seed may be attributed to the activation of anaerobic respiration.