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Bicarbonate-controlled reduction of oxygen by the QA semiquinone in Photosystem II in membranes.
Fantuzzi, A, Allgöwer, F, Baker, H, McGuire, G, Teh, WK, Gamiz-Hernandez, AP, Kaila, VRI, Rutherford, AW
Proceedings of the National Academy of Sciences of the United States of America. 2022;(6)
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Abstract
Photosystem II (PSII), the water/plastoquinone photo-oxidoreductase, plays a key energy input role in the biosphere. [Formula: see text], the reduced semiquinone form of the nonexchangeable quinone, is often considered capable of a side reaction with O2, forming superoxide, but this reaction has not yet been demonstrated experimentally. Here, using chlorophyll fluorescence in plant PSII membranes, we show that O2 does oxidize [Formula: see text] at physiological O2 concentrations with a t1/2 of 10 s. Superoxide is formed stoichiometrically, and the reaction kinetics are controlled by the accessibility of O2 to a binding site near [Formula: see text], with an apparent dissociation constant of 70 ± 20 µM. Unexpectedly, [Formula: see text] could only reduce O2 when bicarbonate was absent from its binding site on the nonheme iron (Fe2+) and the addition of bicarbonate or formate blocked the O2-dependant decay of [Formula: see text] These results, together with molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics calculations, indicate that electron transfer from [Formula: see text] to O2 occurs when the O2 is bound to the empty bicarbonate site on Fe2+ A protective role for bicarbonate in PSII was recently reported, involving long-lived [Formula: see text] triggering bicarbonate dissociation from Fe2+ [Brinkert et al, Proc. Natl. Acad. Sci. U.S.A. 113, 12144-12149 (2016)]. The present findings extend this mechanism by showing that bicarbonate release allows O2 to bind to Fe2+ and to oxidize [Formula: see text] This could be beneficial by oxidizing [Formula: see text] and by producing superoxide, a chemical signal for the overreduced state of the electron transfer chain.
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Effect of Waters Enriched in O2 by Injection or Electrolysis on Performance and the Cardiopulmonary and Acid-Base Response to High Intensity Exercise.
Daussin, FN, Péronnet, F, Charton, A, Lonsdorfer, E, Doutreleau, S, Geny, B, Richard, R
Nutrients. 2021;(12)
Abstract
Several brands of water enriched with O2 (O2-waters) are commercially available and are advertised as wellness and fitness waters with claims of physiological and psychological benefits, including improvement in exercise performance. However, these claims are based, at best, on anecdotal evidence or on a limited number of unreliable studies. The purpose of this double-blind randomized study was to compare the effect of two O2-waters (~110 mg O2·L-1) and a placebo (10 mg O2·L-1, i.e., close to the value at sea level, 9-12 mg O2·L-1) on the cardiopulmonary responses and on performance during high-intensity exercise. One of the two O2-waters and the placebo were prepared by injection of O2. The other O2-water was enriched by an electrolytic process. Twenty male subjects were randomly allocated to drink one of the three waters in a crossover study (2 L·day-1 × 2 days and 15 mL·kg-1 90 min before exercise). During each exercise trial, the subjects exercised at 95.9 ± 4.7% of maximal workload to volitional fatigue. Exercise time to exhaustion and the cardiopulmonary responses, arterial lactate concentration and pH were measured. Oxidative damage to proteins, lipids and DNA in blood was assessed at rest before exercise. Time to exhaustion (one-way ANOVA) and the responses to exercise (two-way ANOVA [Time; Waters] with repeated measurements) were not significantly different among the three waters. There was only a trend (p = 0.060) for a reduction in the time constant of the rapid component of VO2 kinetics with the water enriched in O2 by electrolysis. No difference in oxidative damage in blood was observed between the three waters. These results suggest that O2-water does not speed up cardiopulmonary response to exercise, does not increase performance and does not trigger oxidative stress measured at rest.
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HYPOXIA AND REPRODUCTIVE HEALTH: Hypoxic regulation of preimplantation embryos: lessons from human embryonic stem cells.
Houghton, FD
Reproduction (Cambridge, England). 2021;(1):F41-F51
Abstract
Development of the preimplantation embryo is reliant on nutrients present in the milieu of the reproductive tract. While carbohydrates, amino acids, lipids, and micronutrients are often considered when discussing preimplantation embryo nutrition, environmental oxygen is frequently overlooked. Although oxygen is not classically considered a nutrient, it is an important component of the in vitro culture environment and a critical regulator of cellular physiology. Oxygen is required to sustain an oxidative metabolism but when oxygen becomes limited, cells mount a physiological response driven by a family of transcription factors termed 'hypoxia inducible factors' which promote expression of a multitude of oxygen sensitive genes. It is this hypoxic response that is responsible not only for the switch to a glycolytic metabolism but also for a plethora of other cellular responses. There has been much debate in recent years over which environmental oxygen tension is preferential for the culture of preimplantation embryos. The review will evaluate this question and highlights how research using human embryonic stem cells can inform our understanding of why culturing under physiological oxygen tensions may be beneficial for the development of embryos generated through clinical in vitro fertilisation.
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Identification of Oxygen-Independent Pathways for Pyridine Nucleotide and Coenzyme A Synthesis in Anaerobic Fungi by Expression of Candidate Genes in Yeast.
Perli, T, Vos, AM, Bouwknegt, J, Dekker, WJC, Wiersma, SJ, Mooiman, C, Ortiz-Merino, RA, Daran, JM, Pronk, JT
mBio. 2021;(3):e0096721
Abstract
Neocallimastigomycetes are unique examples of strictly anaerobic eukaryotes. This study investigates how these anaerobic fungi bypass reactions involved in synthesis of pyridine nucleotide cofactors and coenzyme A that, in canonical fungal pathways, require molecular oxygen. Analysis of Neocallimastigomycetes proteomes identified a candidate l-aspartate-decarboxylase (AdcA) and l-aspartate oxidase (NadB) and quinolinate synthase (NadA), constituting putative oxygen-independent bypasses for coenzyme A synthesis and pyridine nucleotide cofactor synthesis. The corresponding gene sequences indicated acquisition by ancient horizontal gene transfer (HGT) events involving bacterial donors. To test whether these enzymes suffice to bypass corresponding oxygen-requiring reactions, they were introduced into fms1Δ and bna2Δ Saccharomyces cerevisiae strains. Expression of nadA and nadB from Piromyces finnis and adcA from Neocallimastix californiae conferred cofactor prototrophy under aerobic and anaerobic conditions. This study simulates how HGT can drive eukaryotic adaptation to anaerobiosis and provides a basis for elimination of auxotrophic requirements in anaerobic industrial applications of yeasts and fungi. IMPORTANCE NAD (NAD+) and coenzyme A (CoA) are central metabolic cofactors whose canonical biosynthesis pathways in fungi require oxygen. Anaerobic gut fungi of the Neocallimastigomycota phylum are unique eukaryotic organisms that adapted to anoxic environments. Analysis of Neocallimastigomycota genomes revealed that these fungi might have developed oxygen-independent biosynthetic pathways for NAD+ and CoA biosynthesis, likely acquired through horizontal gene transfer (HGT) from prokaryotic donors. We confirmed functionality of these putative pathways under anaerobic conditions by heterologous expression in the yeast Saccharomyces cerevisiae. This approach, combined with sequence comparison, offers experimental insight on whether HGT events were required and/or sufficient for acquiring new traits. Moreover, our results demonstrate an engineering strategy for enabling S. cerevisiae to grow anaerobically in the absence of the precursor molecules pantothenate and nicotinate, thereby contributing to alleviate oxygen requirements and to move closer to prototrophic anaerobic growth of this industrially relevant yeast.
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Effect on splanchnic oxygenation of breast milk, fortified breast milk, and formula milk in preterm infants.
Dani, C, Coviello, C, Montano, S, Remaschi, G, Petrolini, C, Strozzi, MC, Maggiora, E, Sabatini, M, Gazzolo, D
Pediatric research. 2021;(1):171-174
Abstract
BACKGROUND Enteral feeding induces mesenteric hemodynamic changes in preterm infants, which may vary according to the milk used. Our aim in this study was to evaluate changes of splanchnic regional oxygenation (rSO2S) measured by near-infrared spectroscopy (NIRS) in infants fed with mother's own milk (MOM), fortified human milk (FHM), or preterm formula (PTF). METHODS Infants born at 25-31 weeks of gestational age (n = 54) received a bolus of MOM, FHM, or PTF. rSO2S and splanchnic fractional oxygen extraction ratio (FOES) were recorded 60 min before (T0), and 30 min (T1) and 120 min (T2) after the beginning of bolus feeding. RESULTS In the MOM group, rSO2S and FOES did not change during the study period. In the FBM group, rSO2S decreased from T0 to T1 and increased from T1 to T2, while FOES changed in reverse. In the PTF group, rSO2S decreased from T0 to T1 and from T1 to T2, while FOES changed in reverse. CONCLUSIONS Splanchnic oxygenation was not affected by MOM feeding, was transiently decreased by FBM feeding, and was persistently decreased by PTF. These results suggest that preterm infants who received PTF has higher splanchnic tissue oxygen extraction compared to those who received MOM or FBM. IMPACT Human milk feeding is associated to a lower splanchnic energy expenditure than preterm formula feeding. Fortified human milk transiently increases splanchnic energy expenditure. Preterm formula should be used only in the absence of human milk.
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How Oxygen Binding Enhances Long-Range Electron Transfer: Lessons From Reduction of Lytic Polysaccharide Monooxygenases by Cellobiose Dehydrogenase.
Wang, Z, Feng, S, Rovira, C, Wang, B
Angewandte Chemie (International ed. in English). 2021;(5):2385-2392
Abstract
Long-range electron transfer (ET) in metalloenzymes is a general and fundamental process governing O2 activation and reduction. Lytic polysaccharide monooxygenases (LPMOs) are key enzymes for the oxidative cleavage of insoluble polysaccharides, but their reduction mechanism by cellobiose dehydrogenase (CDH), one of the most commonly used enzymatic electron donors, via long-range ET is still an enigma. Using multiscale simulations, we reveal that interprotein ET between CDH and LPMO is mediated by the heme propionates of CDH and solvent waters. We also show that oxygen binding to the copper center of LPMO is coupled with the long-range interprotein ET. This process, which is spin-regulated and enhanced by the presence of O2 , directly leads to LPMO-CuII -O2- , bypassing the formation of the generally assumed LPMO-CuI species. The uncovered ET mechanism rationalizes experimental observations and might have far-reaching implications for LPMO catalysis as well as the O2 - or CO-binding-enhanced long-range ET processes in other metalloenzymes.
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A Computational Study of the S2 State in the Oxygen-Evolving Complex of Photosystem II by Electron Paramagnetic Resonance Spectroscopy.
Baituti, B, Odisitse, S
Molecules (Basel, Switzerland). 2021;(9)
Abstract
The S2 state produces two basic electron paramagnetic resonance signal types due to the manganese cluster in oxygen-evolving complex, which are influenced by the solvents, and cryoprotectant added to the photosystem II samples. It is presumed that a single manganese center oxidation occurs on S1 → S2 state transition. The S2 state has readily visible multiline and g4.1 electron paramagnetic resonance signals and hence it has been the most studied of all the Kok cycle intermediates due to the ease of experimental preparation and stability. The S2 state was studied using electron paramagnetic resonance spectroscopy at X-band frequencies. The aim of this study was to determine the spin states of the g4.1 signal. The multiline signal was observed to arise from a ground state spin ½ centre while the g4.1 signal generated at ≈140 K NIR illumination was proposed to arise from a spin 52 center with rhombic distortion. The 'ground' state g4.1 signal was generated solely or by conversion from the multiline. The data analysis methods used involved numerical simulations of the experimental spectra on relevant models of the oxygen-evolving complex cluster. A strong focus in this paper was on the 'ground' state g4.1 signal, whether it is a rhombic 52 spin state signal or an axial 32 spin state signal. The data supported an X-band CW-EPR-generated g4.1 signal as originating from a near rhombic spin 5/2 of the S2 state of the PSII manganese cluster.
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Therapeutic targeting of the hypoxic tumour microenvironment.
Singleton, DC, Macann, A, Wilson, WR
Nature reviews. Clinical oncology. 2021;(12):751-772
Abstract
Hypoxia is prevalent in human tumours and contributes to microenvironments that shape cancer evolution and adversely affect therapeutic outcomes. Historically, two different tumour microenvironment (TME) research communities have been discernible. One has focused on physicochemical gradients of oxygen, pH and nutrients in the tumour interstitium, motivated in part by the barrier that hypoxia poses to effective radiotherapy. The other has focused on cellular interactions involving tumour and non-tumour cells within the TME. Over the past decade, strong links have been established between these two themes, providing new insights into fundamental aspects of tumour biology and presenting new strategies for addressing the effects of hypoxia and other microenvironmental features that arise from the inefficient microvascular system in solid tumours. This Review provides a perspective on advances at the interface between these two aspects of the TME, with a focus on translational therapeutic opportunities relating to the elimination and/or exploitation of tumour hypoxia.
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Cortical Oxygenation Changes during Gastric Tube Feeding in Moderate- and Late-Preterm Babies: A NIRS Study.
Muelbert, M, Alexander, T, Pook, C, Jiang, Y, Harding, JE, Bloomfield, FH
Nutrients. 2021;(2)
Abstract
Smell and taste of food can trigger physiological responses facilitating digestion and metabolism of nutrients. Controlled experimental studies in preterm babies have demonstrated that smell activates the orbitofrontal cortex (OFC) but none have investigated the effect of taste stimulation. Using cotside Near-Infrared Spectroscopy (NIRS), we measured changes in OFC cerebral oxygenation in response to gastric tube feeds five and 10 days after birth in 53 assessments of 35 moderate- to late-preterm babies enrolled in a randomized trial. Babies were randomly assigned to receive smell and taste of milk before gastric tube feeds (intervention group, n = 16) or no exposure (control group, n = 19). The majority of babies were born at 33 weeks of gestation (range 32-34) and 69% were boys. No differences in OFC cerebral oxygenation were observed between control and intervention groups. Gastric tube feeds induced activation of the OFC (p < 0.05), but sensory stimulation alone with smell and taste did not. Boys, but not girls, showed activation of the OFC following exposure to smell of milk (p = 0.01). The clinical impact of sensory stimulation prior to tube feeds on nutrition of preterm babies, as well as the impact of environmental inputs on cortical activation, remains to be determined.
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Long-Term Outcomes of Radical Radiation Therapy with Hypoxia Modification with Biomarker Discovery for Stratification: 10-Year Update of the BCON (Bladder Carbogen Nicotinamide) Phase 3 Randomized Trial (ISRCTN45938399).
Song, YP, Mistry, H, Irlam, J, Valentine, H, Yang, L, Lane, B, West, C, Choudhury, A, Hoskin, PJ
International journal of radiation oncology, biology, physics. 2021;(5):1407-1415
Abstract
PURPOSE Many muscle-invasive bladder cancers are hypoxic, which limits the efficacy of radiation therapy. Hypoxia modification using carbogen and nicotinamide has been tested in a phase 3 trial, Bladder Carbogen Nicotinamide. We present mature follow-up data with biomarker predictions of outcomes. METHODS AND MATERIALS Bladder Carbogen Nicotinamide is a prospective, phase 3, multicenter, randomized, 2-arm, nonblinded clinical trial. Participants were randomized to receive radical radiation therapy (RT; control arm) alone or with the addition of carbogen (98% O2; 2% CO2) and nicotinamide (CON). Patients with muscle-invasive or high-grade non-muscle invasive bladder cancer were included. Tumor tissue was collected at entry and was analyzed for tumor necrosis, hypoxia (24-gene signature), and basal and luminal tumor molecular subtypes. Overall survival (OS) and disease-free survival and relationships with biomarker status outcomes are analyzed using multivariable Cox regression and log-rank analysis. RESULTS We analyzed 333 patients with a median follow-up of 10.3 years. The 10-year OS rates were 30% (95% confidence interval [CI], 0.23-0.39) in RT + CON patients and 24% (95% CI, 0.18-0.33) in the RT-alone patients (hazard ratio [HR], 0.80; 95% CI, 0.61-1.04; P = .08). The greatest benefit from CON was seen in patients with tumor necrosis (n = 79; 5-year OS, 53% vs. 33% in patients without tumor necrosis; HR, 0.59; 95% CI, 0.36-0.99; P = .04). Cases with a high hypoxia gene score (n = 75) had a 5-year OS rate of 51%, compared to 34% for a low score (HR, 0.64; 95% CI, 0.38-1.08; P = .09); those with the basal molecular subtype (n = 70) had a 5-year OS rate of 58%, compared to 38% for those with the luminal subtype (HR, 0.58; 95% CI, 0.32-1.06; P = .08). CONCLUSIONS Although the improvement in long-term OS in the whole population is not statistically significant, patients selected by necrosis and high hypoxia gene score benefitted from hypoxia modification.