The determination of the diiron core intermediate structures involved in the catalytic cycle of soluble methane monooxygenase (sMMO), the enzyme that selectively catalyzes the conversion of methane to methanol, has been a subject of intense interest within the bioinorganic scientific community. Particularly, the specific geometry and electronic structure of the intermediate that precedes methane binding, known as intermediate Q (or MMOH), has been debated for over 30 years. Some reported studies support a bis-μ-oxo-bridged Fe(IV)O closed-core conformation Fe(IV)O core, whereas others favor an open-core geometry, with a longer Fe-Fe distance. The lack of consensus calls for a thorough re-examination and reinterpretation of the spectroscopic data available on the MMOH intermediate. Herein, we report extensive simulations based on a hybrid quantum mechanics/molecular mechanics approach (QM/MM) approach that takes into account the complete enzyme to explore possible conformations for intermediates MMOH and MMOH of the sMMOH catalytic cycle. High-level quantum chemical approaches are used to correlate specific structural motifs with geometric parameters for comparison with crystallographic and EXAFS data, as well as with spectroscopic data from Mössbauer spectroscopy, Fe K-edge high-energy resolution X-ray absorption spectroscopy (HERFD XAS), and resonance Raman O-O difference spectroscopy. The results provide strong support for an open-core-type configuration in MMOH, with the most likely topology involving mono-oxo-bridged Fe ions and alternate terminal Fe-oxo and Fe-hydroxo groups that interact via intramolecular hydrogen bonding. The implications of an open-core intermediate Q on the reaction mechanism of sMMO are discussed.
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http://dx.doi.org/10.1021/jacs.1c01180 | DOI Listing |
Dalton Trans
January 2025
Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan.
The Ru(IV,IV), Ru(III,IV), and Ru(III,III) complexes with the doubly oxido- and/or hydroxido-bridged diamond core {Ru(μ-O(H))}, bridged by an η:η:μ-type bidentate sulfato ligand, [{Ru(L)}(μ-O)(μ-OSO)] ( = 1: [III,IV]; = 2: [IV,IV]), [{Ru(L)}(μ-O)(μ-OH)(μ-OSO)] ([III,IV_1H]), and [{Ru(L)}(μ-OH)(μ-OSO)] ([III,III_2H]) (L = ethylbis(2-pyridylmethyl)amine), were synthesised as ClO-salts, and their crystal and electronic structures investigated. The corresponding hydrogencarbonato-bridged Ru(III,III) complex, [{Ru(L)}(μ-OH)(μ-OCOH)] ([III,III(HCO3)_2H]), was also prepared and its crystallographic and electronic structures compared to those of the sulfato-bridged system, [III,III_2H]. All the sulfato-bridged complexes isolated were confirmed in the Pourbaix diagram, wherein the redox potential was plotted as a function of pH.
View Article and Find Full Text PDFAten Primaria
January 2025
Medicina Familiar y Comunitaria, Centro de Salud Los Ángeles, Madrid; Grupo de trabajo de Patología digestiva y hepática de la semFYC; Grupo de trabajo de Digestivo de la SoMaMFyC, España.
The small intestine bacterial overgrowth (SIBO) is a clinical disorder resulting from colonization of the small intestine by an excessive number of microorganisms or by unusual microorganisms. When they are methane producers it is called intestinal methanogen overgroth (IMO). Known risk factors are congenital or acquired anatomical alterations, motility alterations, some systemic and autoimmune diseases, those that cause alterations in biliopancreatic secretions, hypochlorhydria and some drugs.
View Article and Find Full Text PDFTrop Anim Health Prod
January 2025
Department of Animal and Fish Production, Faculty of Agriculture (El-Shatby), Alexandria University, Alexandria, 21545, Egypt.
Pomegranate peels are an industrial by-product high in sugar and phytochemical content and pose an environmental concern. Meanwhile, ensiling legume forage such as berseem is difficult due to its lower dry matter content and water-soluble carbohydrate-to-buffering capacity ratio, which leads to a poor fermentation process. To date, no studies have been conducted to investigate the effect of co-ensiling pomegranate peels with berseem.
View Article and Find Full Text PDFPLoS One
January 2025
Environmental Molecular Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, United States of America.
Coastal wetlands, including freshwater systems near large lakes, rapidly bury carbon, but less is known about how they transport carbon either to marine and lake environments or to the atmosphere as greenhouse gases (GHGs) such as carbon dioxide and methane. This study examines how GHG production and organic matter (OM) mobility in coastal wetland soils vary with the availability of oxygen and other terminal electron acceptors. We also evaluated how OM and redox-sensitive species varied across different size fractions: particulates (0.
View Article and Find Full Text PDFChemosphere
January 2025
Guangxi Key Laboratory of Environmental Processes and Remediation in Ecologically Fragile Regions, Guangxi Normal University, 15 Yucai Road, Guilin, 541004, PR China; Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education, 15 Yucai Road, Guilin, 541004, PR China. Electronic address:
Garlic and chili are widely used as food flavoring agents in food cooking, therefore might be accumulated in large amounts in food waste (FW). The effects of garlic and chili on the dissolution, hydrolysis, acidification and methanation in an anaerobic co-digestion system were investigated during the combined co-digestion of FW and excess sludge (ES). Additionally, the transformation of phosphorus form and microbial metabolism changes during the process were analyzed.
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