384 research outputs found
Relationship between ectoenzymatic activity and availability of organic substrates (Ross Sea, Antarctica): An experimental approach
No full textOrganic matter consumption and decomposition were studied in four experimental systems, having collected different organic substrates in the Ross Sea in December 1994. For the experimental approach selected, processes normally acting on a mixed pool of substances could be separated and the main features of each phenomenon could be focused on. Through the strict relationship between each experimental system and natural conditions shown by organic matter assessment, ectoenzymatic activity trends and their relation with Antarctic water substrates could be described. Through ice melting the water column becomes rich in large pools of substrates, as well as enzyme-producing micro-organisms, capable of quick development. The quantitative predominance of leucine-aminopeptidase throughout the year is well known, but its relative importance seems to decrease when, owing to production events, the environment is enriched with autotrophic- and heterotrophic-derived substances, leading to glycolytic enzymes expression. Thus, ectoenzymatic activity is supposed to be one of the factors responsible for organic matter variations, showing quantitative and qualitative changes depending on substrate availability
Regulation of mtDNA gene expression and the role of respiratory chain supercomplexes in mammalian mitochondria
No full textMitochondria are cellular organelles found in nearly all eukaryotic cells, where they fulfill a plethora of functions, including energy conversion. They harness energy from carbon sources to synthesize adenosine triphosphate (ATP) through the process of oxidative phosphorylation (OXPHOS). Mammalian mitochondria contain ~1200 proteins and only 13 of these are encoded by mitochondrial DNA (mtDNA). Despite the small contribution to the mitochondrial proteome, expression of mtDNA is nevertheless critically important for biogenesis and normal function of the OXPHOS system. The expression of mtDNA is dependent on ~200 nucleus-encoded proteins that are imported into mitochondria to control maintenance, replication, and transcription of mtDNA, as well as translation of the mtDNA-encoded messenger RNAs (mRNAs). Mitochondrial gene expression is thus controlled at many different levels. In the first part of this thesis, molecular mechanisms are reported for initiation and completion of mtDNA replication. Furthermore, mechanisms controlling the switch from transcription initiation to elongation, as well as a putative link between transcription elongation and RNA processing are reported. These results were based on extensive analysis of conditional knockout mouse models for RNase H1, TEFM, and mtSSB. In the second part of the thesis, the organization of the OXPHOS system is studied. It consists of the respiratory chain enzyme complexes, two electron shuttles and the ATP synthase. A wide range of studies have shown that the different respiratory chain enzyme complexes can interact with each other to form higher order assemblies, so called supercomplexes. The respirasome is a particularly interesting supercomplex as it consists of a complete respiratory chain. Results from multiple studies have suggested that the respirasome plays a crucial role in cellular bioenergetics by facilitating translocation and routing of electrons. To address this question, we extensively characterized a knockin mouse model engineered to have normal levels of respiratory chain complexes that cannot interact to form respirasomes. Surprisingly, mice with drastically reduced levels of respirasomes are healthy without any clear impact on bioenergetics or whole animal physiology. Our results thus challenge the multiple proposed roles for respirasomes in physiology and disease.List of scientific papersI. Jelena Misic, Dusanka Milenkovic, Ali Al-Behadili, Xie Xie, Min Jiang, Shan Jiang, Roberta Filograna, Camilla Koolmeister, Stefan J. Siira, Louise Jenninger, Aleksandra Filipovska, Anders R. Clausen, Leonardo Caporali, Maria Lucia Valentino, Chiara La Morgia, Valerio Carelli, Thomas J. Nicholls, Anna Wredenberg, Maria Falkenberg, Nils-Göran Larsson†. (2022). Mammalian RNase H1 directs RNA primer formation for mtDNA replication initiation and is also necessary for mtDNA replication completion. Nucleic Acids Res. 50, 8749–8766. †Corresponding author(s). https://doi.org/10.1093/nar/gkac661 II. Shan Jiang, Camilla Koolmeister, Jelena Misic, Stefan Siira, Inge Kühl, Eduardo Silva Ramos, Maria Miranda, Min Jiang, Viktor Posse, Oleksandr Lytovchenko, Ilian Atanassov, Florian A. Schober, Rolf Wibom, Kjell Hultenby, Dusanka Milenkovic, Claes M. Gustafsson, Aleksandra Filipovska, Nils-Göran Larsson†. (2019). TEFM regulates both transcription elongation and RNA processing in mitochondria. EMBO Rep. 20, 1–18. †Corresponding author(s). https://doi.org/10.15252/embr.201948101 III. Min Jiang*, Xie Xie*, Xuefeng Zhu*, Shan Jiang, Dusanka Milenkovic, Jelena Misic, Yonghong Shi, Nirwan Tandukar, Xinping Li, Ilian Atanassov, Louise Jenninger, Emily Hoberg, Sara Albarran-Gutierrez, Zsolt Szilagyi, Bertil Macao, Stefan J. Siira, Valerio Carelli, Jack D. Griffith, Claes M. Gustafsson, Thomas J. Nicholls, Aleksandra Filipovska, Nils-Göran Larsson†, Maria Falkenberg†. (2021). The mitochondrial single-stranded DNA binding protein is essential for initiation of mtDNA replication. Sci Adv. 7, eabf8631. *These authors contributed equally. †Corresponding author(s). https://doi.org/10.1126/sciadv.abf8631 IV. Dusanka Milenkovic, Jelena Misic, Johannes F. Hevler, Thibaut Molinié, Injae Chung, Ilian Atanassov, Xinping Li, Roberta Filograna, Andrea Mesaros, Arnaud Mourier, Albert J.R. Heck, Judy Hirst†, Nils-Göran Larsson†. (2023). Preserved respiratory chain capacity and physiology in mice with profoundly reduced levels of mitochondrial respirasomes. Cell Metab. 35, 1799-1813.e7. †Corresponding author(s). https://doi.org/10.1016/j.cmet.2023.07.015 </p
LAND FORCING CONTROLS PELAGIC-BENTHIC COUPLING IN ADELIE COVE (TERRA NOVA BAY, ROSS SEA)
No full textBenthic-pelagic coupling processes were studied in Adelie Cove, a small 70-m deep V-shaped bay, located on the coast of Terra Nova Bay (Ross Sea). This cove is set apart from the open sea by a 12- to 15-m deep sill. Samplings were carried out over 20 days in summer 1997/1998 in the water column, in the sediment and in material collected from the sea-bottom interface by means of a sediment trap. Benthic communities were studied mainly using ROV video tapes. The complex and peculiar interactions between physical, chemical and biological processes, both in the water column and in the sediments, were tightly linked to a katabatic wind pattern, which is the main constraint in water mass circulation. A clear evolution in organic matter distribution and composition was observed. These processes led to a high build-up of materials in the sediments in the deepest part of the cove, which favoured deposit-feeding species and largely contributed to the organic enrichment of the sediments
Particulate organic matter composition in a semi-enclosed Periantarctic system: the Straits of Magellan
No full textSUMMARY: The elemental and biochemical composition of particulate organic matter (POM) was investigated in the Straits of Magellan during February-March 1991. Twenty-two stations were selected in order to identify different areas of the Magellan ecosystem from a trophic point of view. The Strait of Magellan can be divided into three subsystems charac-terized by different hydrological and geomorphological conditions. Seston concentrations were mostly constrained by phys-ical events, particularly the influence of oceanic and land run-off water inputs and the strong vertical mixing and resuspen-sion events. POM composition displayed quali-quantitative differences between the three areas. In the first subsystem, influ-enced by Pacific waters, the low seston and POM concentrations and the high POC/Chl-a ratio values indicated the gener-al predominance of the detrital and heterotrophic fractions. In the second subsystem, characterized by superficial stratifica-tion, higher seston and organic matter concentrations and lower values of POC/Chl-a ratio were found, indicating that this subsystem was influenced by an active autotrophic component. Shallow waters with intense tidal regime and strong verti-cal mixing characterized the third subsystem, connected to the Atlantic Ocean, which displayed an increasing importance of the inorganic fraction (values of the POC/TSM ratio lower than in the other systems). Moreover, the third subsystem showed higher values of the RNA/DNA ratio, possibly indicating that resuspension events may enhance the metabolic state of th
Enzymatic activity and organic substrates on a sandy beach of the Ligurian Sea (NW Mediterranean) influenced by anthropogenic pressure.
No full textEnzymatic activities (leucine aminopeptidase, LA; β-glucosidase, BG; alkaline phosphatase,AP), their related substrates and the bacterial abundance and biomass were studied over 1 yr in 2 adjacent areas of a sandy beach: one occupied by the structures of a private swimming establishment and undergoing major reconstruction work (impacted area), and the other in a more natural
area (reference area). Both areas were oligotrophic, characterised by low organic matter content
(with a notable contribution from the autotrophic biomass) and low enzymatic activity values. Bacterial abundance did not show significant changes, either spatially or temporally, suggesting that they quickly overcame anthropogenic forcing and seasonal luctuations under the environmental and
trophic conditions. The absence of positive correlations between carbohydrates and enzymatic activities
suggested the adverse influence of refractory organic matter. Nevertheless, when the environmental
conditions were favourable and bacteria were supported by larger N inputs from the sea, the
carbohydrate became a trophic resource, thus suddenly changing the enzyme ratios. A multivariate
analysis highlighted the predominance of the seasonal over the anthropogenic influence, suggesting
a rapid recovery in the impacted area. Nevertheless, changes were observed for the functional relationships
between the parameters, in particular those related to the trophic quality of the organic material (lower in the impacted area) and the enzymatic hydrolysis. The coupling of LA and AP was generally tight in order to overcome the P deficiency and, in the impacted area, to overcome trophic
limitations related to the input of inorganic debris and refractory organic materials
UV-SLPT for gas sensor research on MISiC devices
No full textA modified Scanning Light Pulse Technique (SLPT) setup that can be used to evaluate SiC-based gas-sensitive field-effect devices is introduced. This is exemplified with measurements on a Pt-MISiC capacitor that has a metal thickness gradient. The device shows large responses to hydrogen and ammonia in air. The H-2 and NH3 responses show a complementary dependence on the Pt film thickness at 140 degrees C. The temperature dependence differs however for the two gases. The measurement setup uses UV transparent optics together with mechanical chopping of light from a short wavelength light source. The spatial resolution of the system is found to be approximately 50 mu m.</p
Determination of Optimal Insulaor Thickness for MISiC Hydrogen Sensors
No full textResponse mechanisms of hydrogen sensor based on a metal-insulator-SiC (MISiC) Schottky-barrier diode are analyzed. A physical model is established for the hydrogen sensor by combining thermionic emission with quantum-mechanical tunneling of charge carriers, and considering hydrogen-induced barrier-height modulation. Simulated results are in good agreement with experimental data. Relation between device performance and insulator thickness is investigated using the proposed model, and the optimal range of insulator thickness can be determined by taking into account the tradeoff between device sensitivity, reliability and resolution for high-temperature applications. © 2004 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex
Detection of HC in exhaust gases by an array of MISiC sensors
No full textFuture legislations for car emissions make direct measurements in exhaust gases of hydrocarbon (HC) as well as CO and NOx interesting. Robust sensors that can stand the high temperature and rough environment in the exhaust gases are needed. Silicon carbide has the advantage of being a chemically very inert material, which, due to its high band gap, is a semiconductor even at temperatures around 800°C. Catalytic metal insulator silicon carbide Schottky diode sensors respond to gases like H2, HC, NOx in exhaust gases. The choice of catalytic metal, structure of the metal, and the operation temperature determines the response pattern to different gases. Here we will demonstrate that an array of different MISiC sensors to some extent predicts the HC concentration in gasoline exhaust gases. Chemometric methods are used for the evaluation of the signals. © 2001 Elsevier Science B.V.</p
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