Academic literature on the topic 'O2-responsive'

ABSTRACT Clostridium acetobutylicum, an obligate anaerobe, grows normally under continuous-O2-flow culture conditions, where the cells consume O2 proficiently. An O2-responsive NADH:rubredoxin oxidoreductase operon composed of three genes (nror, fprA2, and dsr), encoding NROR, functionally uncharacterized flavoprotein A2 (FprA2), and the predicted superoxide reductase desulfoferrodoxin (Dsr), has been proposed to participate in defense against O2 stress. To functionally characterize these proteins, native NROR from C. acetobutylicum, recombinant NROR (rNROR), FprA2, Dsr, and rubredoxin (Rd) expressed in Escherichia coli were purified. Purified native NROR and rNROR both exhibited weak H2O2-forming NADH oxidase activity that was slightly activated by Rd. A mixture of NROR, Rd, and FprA2 functions as an efficient H2O-forming NADH oxidase with a high affinity for O2 (the Km for O2 is 2.9 � 0.4 μM). A mixture of NROR, Rd, and Dsr functions as an NADH-dependent O2 − reductase. A mixture of NROR, Rd, and rubperoxin (Rpr, a rubrerythrin homologue) functions as an inefficient H2O-forming NADH oxidase but an efficient NADH peroxidase with a low affinity for O2 and a high affinity for H2O2 (the Km s for O2 and H2O2 are 303 � 39 μM and ≤1 μM, respectively). A gene encoding Rd is dicistronically transcribed with a gene encoding a glutaredoxin (Gd) homologue, and the expression levels of the genes encoding Gd and Rd were highly upregulated upon exposure to O2. Therefore, nror operon enzymes, together with Rpr, efficiently function to scavenge O2, O2 −, and H2O2 by using an O2-responsive rubredoxin as a common electron carrier protein.

A poly(N-isopropylacrylamide) (PIPAAm) grafted poly(dimethylsiloxane) (PDMS) surface was prepared as a temperature-responsive cell culture surface by using electron beam (EB) irradiation. Different chemical treatments to modify the bare PDMS surface were investigated for subsequent grafting of PIPAAm, and treatment conditions were optimized to prepare the temperature-responsive cell culture surface. The PDMS surface was initially activated to form silanol groups with conventional O2 plasma or hydrochloric acid (HCl) treatment. Activated PDMS surfaces were individually immobilized with three different conventional silane compounds, i.e., 3-mercaptopropyltrimethoxysilane (MerTMS), 3-methacryloxypropyltrimethoxysilane (MetTMS), and 3-aminopropyltrimethoxysilane (AmiTMS). O2 plasma treatment made PDMS more hydrophilic. In contrast, PDMS surfaces activated with HCl treatment were relatively hydrophobic. Observation of the activated PDMS surface modified with MerTMS, MetTMS, and AmiTMS indicated that these silane compounds had been favorably immobilized on plasma-treated PDMS surfaces. FT-IR/ATR analysis demonstrated that immobilized silane compounds enabled PIPAAm grafting on the PDMS surface. Cell attachment and detachment analysis also suggested that the PDMS surface sequentially treated with O2 plasma and AmiTMS compound was a substrate appropriate for preparing a temperature-responsive cell culture surface by EB irradiation-induced PIPAAm grafting method. The intelligent surface may further be applied to mechanically stretchable temperature-responsive cell culture surfaces.

The affinity of blood for O2 can now be explained in terms of the interaction of the hemoglobin molecule with cofactors. Recent advances in comparative physiology suggest that short-term compensatory changes in blood O2 affinity, which greatly alter the efficiency of the O2-delivery system in response to hypoxia, are typical for vertebrates. Control of O2 delivery by red blood cell organic phosphates is best interpreted in terms of plasticity of the system, rather than as an adaptive feature responsive to evolutionary selection pressure.

Correction for ‘Microneedle-mediated delivery of MIL-100(Fe) as a tumor microenvironment-responsive biodegradable nanoplatform for O2-evolving chemophototherapy’ by Sulan Luo et al., Biomater. Sci., 2021, DOI: 10.1039/d1bm00888a.

Aprotic lithium-oxygen (Li-O2) batteries have gained extensive interest in the past decade, but are plagued by slow reaction kinetics and induced large-voltage hysteresis. Herein, we use a plasmonic heterojunction of Au nanoparticle (NP)–decorated C3N4 with nitrogen vacancies (Au/NV-C3N4) as a bifunctional catalyst to promote oxygen cathode reactions of the visible light–responsive Li-O2 battery. The nitrogen vacancies on NV-C3N4 can adsorb and activate O2 molecules, which are subsequently converted to Li2O2 as the discharge product by photogenerated hot electrons from plasmonic Au NPs. While charging, the holes on Au NPs drive the reverse decomposition of Li2O2 with a reduced applied voltage. The discharge voltage of the Li-O2 battery with Au/NV-C3N4 is significantly raised to 3.16 V under illumination, exceeding its equilibrium voltage, and the decreased charge voltage of 3.26 V has good rate capability and cycle stability. This is ascribed to the plasmonic hot electrons on Au NPs pumped from the conduction bands of NV-C3N4 and the prolonged carrier life span of Au/NV-C3N4. This work highlights the vital role of plasmonic enhancement and sheds light on the design of semiconductors for visible light–mediated Li-O2 batteries and beyond.

To delineate the roles of O2 and vascular endothelial growth factor (VEGF) in the process of angiogenesis from the embryonic aorta, we cultured mouse embryonic aorta explants (thoracic level to lateral vessels supplying the mesonephros and metanephros) in a three-dimensional type I collagen gel matrix. During 8 days of culture under 5% O2, but not room air, the addition of VEGF to explants stimulated the formation of CD31-positive, Flk-1-positive, Gs-IB4-positive structures in a concentration-dependent manner. Electron microscopy showed the structures to be capillary-like. VEGF-induced capillary-like structure formation was inhibited by sequestration of VEGF via addition of soluble Flt-1 fusion protein or anti-VEGF antibodies. Expression of Flk-1, but not Flt-1, was increased in embryonic aorta cultured under 5% O2 relative to room air. Our data suggest that low O2 upregulates Flk-1 expression in embryonic aorta in vitro and renders it more responsive to VEGF.

Les légumineuses sont connues pour leurs capacités à établir une relation symbiotique avec des bactéries du sol fixatrices de l'azote atmosphérique. Cette interaction aboutit à la formation d'un nouvel organe au niveau des racines, la nodosité, au sein duquel le symbiote convertit l'azote atmosphérique (N2) en ammoniac, qui peut être directement consommé par les plantes. A l’intérieur de cette nodosité, la concentration en oxygène (O2) est maintenue à un très faible niveau car la réaction de réduction du N2 par l’enzyme bactérienne nitrogénase est inhibée par des traces d’oxygène. Un mécanisme de perception directe de l'O2 impliquant des membres de la famille des facteurs de transcription « Ethylene Responsive Factors » (ERFs) du groupe VII a récemment été découvert chez Arabidopsis thaliana. Ces facteurs de transcription (FT) possèdent une extrémité N-terminale caractéristique avec un résidu de cystéine à la seconde position. Dans des conditions normales d'O2, les FT sont conduit à la dégradation suivant une voie spécifique du protéasome. En condition de stress hypoxique, les TFs sont stabilisés et peuvent activer l’expression des gènes de réponse à l'hypoxie. Il a été démontré que la présence d’O2 et de NO était nécessaire pour déstabiliser ces protéines, et qu'une réduction de la disponibilité de l'un ou l'autre des gaz est suffisante pour protéger le résidu cystéine N-terminale de l'oxydation. L’objectif de cette thèse a été d'étudier le rôle de la famille ERF-VII dans la perception et l'adaptation au manque d'O2 chez M. truncatula. Des travaux ont aussi été menés pour déterminer l’importance du NO dans le fonctionnement en microoxie de la nodosité. Quatre gènes codant pour des facteurs de transcription de la famille ERF-VII ont été identifiés dans le génome de M. truncatula. La caractérisation de cette famille au niveau transcriptionnel a révélé que seul MtERF-B2.2 était induit par le stress hypoxique et au cours du développement des nodosités. Les trois autres, MtERF-B1.1, MtERF-B1.11 et MtERF-B2.3, sont constitutivement exprimés dans les feuilles, les racines et les nodosités. Pour étudier la stabilité de la protéine MtERF-B2.1, l’orthologue de RAP2.12 principal ERF-VII décrit dans la perception de l’O2 chez Arabidopsis, en fonction de la disponibilité de O2/NO, nous avons réalisé une protéine de fusion entre l’extrémité N-terminale de notre protéine et la protéine rapporteur luciférase. Les résultats obtenus sur des protoplastes d'Arabidopsis montrent l’implication la partie N-terminale de MtERF-B2.1 dans la régulation de la stabilité de la protéine, mais en contradiction avec les résultats obtenus en plantes composites de M. truncatula. La fonction de MtERF-B2.1 et MtERF-B2.11 a également été étudiée dans le cadre de la réponse au stress hypoxique et au cours du processus de nodulation en utilisant une stratégie d'interférence ARN. Des racines transgéniques dérégulées sur l’expression de MtERF-B2.1 et MtERF-B2.11 ont montré un défaut d’activation de plusieurs gènes de réponses à l'hypoxie tels que l’alcool déshydrogénase (ADH1) ou la pyruvate décarboxylase (PDC1). Ces racines transgéniques ARNi-MtERF-B2.1/B2.11 sont également affectées dans l'interaction symbiotique avec une réduction significative de la capacité de nodulation et de l'activité de fixation de l'azote dans les nodules matures. En conclusion, ces travaux révèlent que le mécanisme de détection d'O2 est médié par les ERF-VII dans les nodosités de M. truncatula et que ce mécanisme, associé aux cibles moléculaires régulées en aval, participe au développement de cet organe et au maintien de la capacité de fixatrice de celui-ci. De plus, les résultats indiquent que MtERF-B2.1/B2.11 sont des régulateurs positifs du métabolisme anaérobie et que les gènes associés au cycle hémoglobine-NO sont susceptibles d'activer d'autres voies de génération d'ATP
Legume crops are known for their capacities to establish a symbiotic relationship with nitrogen fixing soil bacteria. This mutualism culminates in the formation of a new plant organ, the root nodule, in which the symbiont converts atmospheric nitrogen (N2) into ammonia, which can be directly consumed by plants. In nodules, bacterial nitrogenase enzyme is inhibited by traces of oxygen (O2) so different mechanisms maintain this organ at low O2 level. At the same time, nodules need to maintain a high ATP level to support the nitrogenase activity, which is highly energy demanding. Thus, a balance between a tight protection from O2 and an efficient energy production, referred as the “O2 paradox” of N2-fixing legume nodules, has to be reached. In Arabidopsis thaliana, a direct oxygen sensing mechanism has recently been discovered involving members of the ethylene responsive factors (ERFs) group VII. These transcription factors (TFs) possess a characteristic N-terminal amino acid with a cysteine residue at the second position that, under normal O2 conditions, leads to protein degradation following a specific pathway called the N-end rule pathway. Furthermore, it was shown that both O2 and nitric oxide (NO) are required to destabilize the ERFs VII and that a reduction in the availability of either gas is sufficient to stabilize these proteins. Therefore, the goal of this thesis was to investigated the role of ERF-VII family in O2 sensing and adaptation to hypoxia in M. truncatula, model plant for legumes, and to understand how NO interacts with O2 in hypoxic signalization in the microoxic environment that characterizes the nodule. We identified four genes belonging to the ERF-VII TF family in the M. truncatula genome, which present a strong similarity with ERF-VII of Arabidopsis. The characterization of this family at the transcriptional level revealed that only MtERF-B2.2 is up-regulated by hypoxia stress and during nodule development. The three others, MtERF-B1.1, MtERF-B1.11 and MtERF-B2.3 are found constitutively expressed in leaves, roots and nodules. To investigated the protein stability of MtERF-B2.1, the closest orthologous to AtRAP2.12 described as O2-sensors in Arabidopsis, in function of O2/NO availability, we realized a fusion protein with the luciferase reporter protein. Our results on Arabidopsis protoplasts indicated that the N-terminal part of MtERF-B2.1 drives its O2-dependent degradation by the N-end rule pathway. The function of MtERF-B2.1 and MtERF-B2.11 was also investigated both in response to hypoxia stress and during the nodulation process using an RNA interference strategy. Silencing of MtERFB2.1 and MtERF-2.11 showed a significant lower activation of several core hypoxia-responsive genes such as ADH1, PDC1, nsHb1 and AlaAT. These double knock-down transgenic roots were also affected in symbiotic interaction with a significant reduction of the nodulation capacity and nitrogen fixation activity in mature nodules. Overall, the results reveal that O2 sensing mechanism is mediated by ERF-VIIs in M. truncatula roots and nodules and that this mechanism, together with downstream targets, is involved in the organ development and ability to efficiently fix nitrogen. Furthermore, results indicated that MtERF-B2.1/B2.11 are positive regulator of the anaerobic metabolism and the Hb-NO cycle– related genes likely in order to activate alternative ATP generation pathways

Forward Osmosis (FO) process is a low-energy membrane separation technique, which has attracted increasing attention recently for desalination applications. Unlike Reverse Osmosis, which needs a high-pressure pump; FO works via natural osmotic pressure provided by a draw solution. Therefore, development of efficient draw solutions is quite important. Polymeric stimuli-responsive microgels/hydrogels are promising options as they can be recovered by applying the proper stimulus heating or gassing processes. The temperature-responsive microgels/hydrogels have been developed for FO application in recent years. This thesis study was aimed to the development of gas-responsive microgels as draw solutions for FO desalination. Two main series of microgels: CO₂-responsive and O₂-responsive microgels are for the first time fabricated and evaluated for FO desalination throughout the thesis. The feed saline water used here is 2000 ppm NaCl, which is considered as brackish water. A few of polymer monomers with tertiary amine moieties are selected for synthesizing CO₂-responsive microgels. Water flux of the microgels was measured by monitoring conductivity of the saline feed water and interpreting it to the water flux through the membrane. The microgels are active and protonated as a draw solution after CO₂ purging, and can be recovered after CO₂ stripping by N₂ purging. Microgels synthesised with diethylaminoethyl methacrylate (DEAEMA) can provide water flux as high as 56 LMH. Characterization tests are carried out to explore the most-effective microgels with respect to cationic monomers: DEAEMA and dimethylamino ethyl methacrylate (DMAEMA), and the type and concentration of crosslinkers: poly (ethylene glycol diacrylate) (PEGDA), N,N′-methylene-bisacrylamide (BIS) and ethylene glycol dimethacrylate (EGDMA). The microgels are recovered at their isoelectric point, where microgels are not charged and release water easily. O₂-responsive microgels are synthesised and their FO desalination performance is studied systematically. Two Fluoro-containing monomers (2,3,4,5,6 pentafluorostyrene (FS), 2,2,2-trifluoroethyl methacrylate (FM)), which are responsive to oxygen, are selected to copolymerize with four suitable ionic and non-ionic monomers: DEAEMA, Hydroxyethyl methacrylate (HEMA), DMAEMA and N-isopropylacrylamide (NIPAM). The results show that the water recovery ratio can be enhanced if a proper non-ionic monomer like NIPAM is used. The O₂-responsive microgels synthesised by DMAEMA and 5wt% FM monomer can perform the highest water flux up to 29 LMH. The experimental data reveal that HEMA is not a suitable non-ionic monomer to synthesise O₂-responsive microgels as HEMA has –OH groups, which lead to high negative surface charges and affect the water recovery. FO desalination data show that O₂-responsive microgels perform comparable water flux and water recovery capability. Dynamic light scattering (DLS) as the main characterization test for microgels is done. The microgels show larger hydrodynamic diameter after CO₂ or O₂ purging and they become smaller after removing these gases via N₂ purging. The swelling ratio for the microgels is up to 14 and 6.5 for CO₂ responsive and O₂-responsive microgels, respectively. As new polymer draw agents, CO₂- and O₂-responsive microgels demonstrate high water flux and water recovery capabilities as promising draw solutes for energy-effective FO desalination. CO₂-responsive DEAEMA microgels with 1wt% PEGDA crosslinker performed water flux of 56 LMH with 50 % water recovery ratio. DMAEMA CO₂-responsive microgels perform smaller water flux due to lower pKₐ of DMAEMA than DEAEMA. O₂-responsive microgels show relatively lower water flux than CO₂-responsive microgels. The best water flux performance is observed for DEAEMA/DMAEMA-5wt% FM microgels with 26-29 LMH, while the highest water recovery is given by NIPAM-5wt% FM microgels with 56%.
Thesis (M.Phil.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2018.