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"Lancaster, M"
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Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase
Ammonia (NH₃)-oxidizing bacteria (AOB) emit substantial amounts of nitric oxide (NO) and nitrous oxide (N₂O), both of which contribute to the harmful environmental side effects of large-scale agriculture. The currently accepted model for AOB metabolism involves NH₃ oxidation to nitrite (NO₂⁻) via a single obligate intermediate, hydroxylamine (NH₂OH). Within this model, the multiheme enzyme hydroxylamine oxidoreductase (HAO) catalyzes the four-electron oxidation of NH₂OH to NO₂⁻. We provide evidence that HAO oxidizes NH₂OH by only three electrons to NO under both anaerobic and aerobic conditions. NO₂⁻ observed in HAO activity assays is a nonenzymatic product resulting from the oxidation of NO by O₂ under aerobic conditions. Our present study implies that aerobic NH₃ oxidation by AOB occurs via two obligate intermediates, NH₂OH and NO, necessitating a mediator of the third enzymatic step.
Journal Article
Beyond fossil fuel–driven nitrogen transformations
How much carbon does it take to make nitric acid? The counterintuitive answer nowadays is quite a lot. Nitric acid is manufactured by ammonia oxidation, and all the hydrogen to make ammonia via the Haber-Bosch process comes from methane. That's without even accounting for the fossil fuels burned to power the process. Chen et al. review research prospects for more sustainable routes to nitrogen commodity chemicals, considering developments in enzymatic, homogeneous, and heterogeneous catalysis, as well as electrochemical, photochemical, and plasma-based approaches. Science , this issue p. eaar6611 Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.
Journal Article
Green Chemistry
Sustainable development, the circular economy and environmental issues are at the forefront of public and Government concern. The field of green chemistry aims to provide environmentally benign products from sustainable resources, using processes that do not harm people or the environment at the same time as helping solve key societal problems such as climate change. Updated throughout, this third edition features an expanded section on legislation, a revised chapter on measurement, and a completely re-written chapter on renewable resources, bringing readers the latest developments in this quickly-growing area. Case studies now include more recent examples of real-world applications from industry to demonstrate how the techniques of green chemistry work in practice. This fascinating textbook is suitable for undergraduate and postgraduate courses covering green chemistry, and it encourages new ways of thinking about how products and processes are developed.
eBook
Synthesis of a copper-supported triplet nitrene complex pertinent to copper-catalyzed amination
Terminal copper-nitrenoid complexes have inspired interest in their fundamental bonding structures as well as their putative intermediacy in catalytic nitrene-transfer reactions. Here, we report that aryl azides react with a copper(I) dinitrogen complex bearing a sterically encumbered dipyrrin ligand to produce terminal copper nitrene complexes with near-linear, short copper–nitrenoid bonds [1.745(2) to 1.759(2) angstroms]. X-ray absorption spectroscopy and quantum chemistry calculations reveal a predominantly triplet nitrene adduct bound to copper(I), as opposed to copper(II) or copper(III) assignments, indicating the absence of a copper–nitrogen multiple-bond character. Employing electron-deficient aryl azides renders the copper nitrene species competent for alkane amination and alkene aziridination, lending further credence to the intermediacy of this species in proposed nitrene-transfer mechanisms.
Journal Article
X-ray Emission Spectroscopy Evidences a Central Carbon in the Nitrogenase Iron-Molybdenum Cofactor
Nitrogenase is a complex enzyme that catalyzes the reduction of dinitrogen to ammonia. Despite insight from structural and biochemical studies, its structure and mechanism await full characterization. An iron-molybdenum cofactor (FeMoco) is thought to be the site of dinitrogen reduction, but the identity of a central atom in this cofactor remains unknown. Fe Kβ x-ray emission spectroscopy (XES) of intact nitrogenase MoFe protein, isolated FeMoco, and the FeMoco-deficient ΔnifB protein indicates that among the candidate atoms oxygen, nitrogen, and carbon, it is carbon that best fits the XES data. The experimental XES is supported by computational efforts, which show that oxidation and spin states do not affect the assignment of the central atom to C⁴⁺. Identification of the central atom will drive further studies on its role in catalysis.
Journal Article
Modulation of Hepatitis C Virus RNA Abundance by a Liver-Specific MicroRNA
MicroRNAs are small RNA molecules that regulate messenger RNA (mRNA) expression. MicroRNA 122 (miR-122) is specifically expressed and highly abundant in the human liver. We show that the sequestration of miR-122 in liver cells results in marked loss of autonomously replicating hepatitis C viral RNAs. A genetic interaction between miR-122 and the 5' noncoding region of the viral genome was revealed by mutational analyses of the predicted microRNA binding site and ectopic expression of miR-122 molecules containing compensatory mutations. Studies with replication-defective RNAs suggested that miR-122 did not detectably affect mRNA translation or RNA stability. Therefore, miR-122 is likely to facilitate replication of the viral RNA, suggesting that miR-122 may present a target for antiviral intervention.
Journal Article
Fast and deep phosphoproteome analysis with the Orbitrap Astral mass spectrometer
Owing to its roles in cellular signal transduction, protein phosphorylation plays critical roles in myriad cell processes. That said, detecting and quantifying protein phosphorylation has remained a challenge. We describe the use of a novel mass spectrometer (Orbitrap Astral) coupled with data-independent acquisition (DIA) to achieve rapid and deep analysis of human and mouse phosphoproteomes. With this method, we map approximately 30,000 unique human phosphorylation sites within a half-hour of data collection. The technology is benchmarked to other state-of-the-art MS platforms using both synthetic peptide standards and with EGF-stimulated HeLa cells. We apply this approach to generate a phosphoproteome multi-tissue atlas of the mouse. Altogether, we detect 81,120 unique phosphorylation sites within 12 hours of measurement. With this unique dataset, we examine the sequence, structural, and kinase specificity context of protein phosphorylation. Finally, we highlight the discovery potential of this resource with multiple examples of phosphorylation events relevant to mitochondrial and brain biology.
Protein phosphorylation plays critical roles in myriad cell processes. In this work, the authors apply new mass spectrometer technology to detect and quantify tens of thousands of protein phosphorylation sites within one hour or less of analysis. This technology has potential to greatly accelerate biological discovery.
Journal Article
Upregulation of miRNA-155 promotes tumour angiogenesis by targeting VHL and is associated with poor prognosis and triple-negative breast cancer
MicroRNA-155 (miR-155) is frequently upregulated in various types of human cancer; however, its role in cancer angiogenesis remains unknown. Here, we demonstrate the role of miR-155 in angiogenesis through targeting von Hippel-Lindau (VHL) tumour suppressor in breast cancer. Ectopic expression of miR-155 induced whereas knockdown of miR-155 inhibited human umbilical vein endothelial cell network formation, proliferation, invasion and migration. Furthermore, mammary fat pad xenotransplantation of ectopically expressed miR-155 resulted in extensive angiogenesis, proliferation, tumour necrosis and recruitment of pro-inflammatory cells such as tumour-associated macrophages. Expression of VHL abrogated these miR-155 effects. Moreover, miR-155 expression inversely correlates with VHL expression level and is associated with late-stage, lymph node metastasis and poor prognosis, as well as triple-negative tumour in breast cancer. These findings indicate that miR-155 has a pivotal role in tumour angiogenesis by downregulation of VHL, and provide a basis for miR-155-expressing tumours to embody an aggressive malignant phenotype, and therefore miR-155 is an important therapeutic target in breast cancer.
Journal Article