The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Per Halkjaer Nielsen - One of the best experts on this subject based on the ideXlab platform.
-
phylogenetic identification and Substrate Uptake patterns of sulfate reducing bacteria inhabiting an oxic anoxic sewer biofilm determined by combining microautoradiography and fluorescent in situ hybridization
Applied and Environmental Microbiology, 2002Co-Authors: Jeppe Lund Nielsen, Satoshi Okabe, Yoshimasa Watanabe, Per Halkjaer NielsenAbstract:We simultaneously determined the phylogenetic identification and Substrate Uptake patterns of sulfate-reducing bacteria (SRB) inhabiting a sewer biofilm with oxygen, nitrate, or sulfate as an electron acceptor by combining microautoradiography and fluorescent in situ hybridization (MAR-FISH) with family- and genus-specific 16S rRNA probes. The MAR-FISH analysis revealed that Desulfobulbus hybridized with probe 660 was a dominant SRB subgroup in this sewer biofilm, accounting for 23% of the total SRB. Approximately 9 and 27% of Desulfobulbus cells detected with probe 660 could take up [14C]propionate with oxygen and nitrate, respectively, as an electron acceptor, which might explain the high abundance of this species in various oxic environments. Furthermore, more than 40% of Desulfobulbus cells incorporated acetate under anoxic conditions. SRB were also numerically important members of H2-utilizing and 14CO2-fixing microbial populations in this sewer biofilm, accounting for roughly 42% of total H2-utilizing bacteria hybridized with probe EUB338. A comparative 16S ribosomal DNA analysis revealed that two SRB populations, related to the Desulfomicrobium hypogeium and the Desulfovibrio desulfuricans MB lineages, were found to be important H2 utilizers in this biofilm. The Substrate Uptake characteristics of different phylogenetic SRB subgroups were compared with the characteristics described to date. These results provide further insight into the correlation between the 16S rRNA phylogenetic diversity and the physiological diversity of SRB populations inhabiting sewer biofilms.
-
in situ characterization of Substrate Uptake by microthrix parvicella using microautoradiography
Water Science and Technology, 1998Co-Authors: Kjaer Andreasen, Per Halkjaer NielsenAbstract:Microthrix parvicella is a filamentous microorganism responsible for bulking and foaming problems in many activated sludge treatment plants. The problems have increased with the introduction of nutrient removal in many countries, and presently, there is no reliable control strategy for M. parvicella . Little is known about the physiology of M. parvicella , and conflicting data exist about its preferred organic Substrates, and whether it is able to be physiologically active under anaerobic and anoxic conditions. In this study, the ability of M. parvicella to take up various radioactively labeled organic compounds was investigated in situ at three nutrient removal plants using a microautoradiographic technique. Of 12 compounds tested under aerobic conditions only the long chain fatty acids (LCFA), oleic acid and palmitic acid, and to some extent a lipid, trioleic acid, were assimilated. None of the simple Substrates such as acetate, propionate, butyrate, glucose, ethanol, glycine and leucine were taken up. Furthermore, the Uptake of oleic acid was compared under anaerobic, anoxic and aerobic conditions, and it was demonstrated that in addition to aerobic conditions M. parvicella was also able to take up oleic acid under anaerobic and anoxic conditions. No difference in Substrate Uptake pattern for M. parvicella was found among the tested activated sludge plants. The results strongly indicate that a better control strategy against M. parvicella must rely on a better understanding of presence and availability of triglycerides and LCFA, and an improved knowledge of the physiology of M. parvicella under anaerobic and anoxic conditions.
-
application of microautoradiography to the study of Substrate Uptake by filamentous microorganisms in activated sludge
Applied and Environmental Microbiology, 1997Co-Authors: Kjaer Andreasen, Per Halkjaer NielsenAbstract:Excessive growth of filamentous microorganisms in activated-sludge treatment plants is a major operational problem which causes poor settlement of activated sludge. An enhanced understanding of the factors controlling growth of different filamentous microorganisms is necessary in order to establish more successful control strategies. In the present study, the in situ Substrate Uptake was investigated by means of microautoradiography. It was demonstrated that the Uptake of labeled organic Substrates by the filamentous microorganisms, during short-term incubation, could be detected by microautoradiography. Viability and respiratory activity of the filaments were also detected by reduction of CTC (5-cyano-2,3-ditolyl tetrazolium chloride) and by incorporation of [(sup3)H]thymidine. Gram, Neisser, and fluorescence staining techniques were used for the localization and identification of the filaments. Activated-sludge samples from five wastewater treatment plants with bulking problems due to filamentous microorganisms were investigated. Microthrix parvicella, Nostocoida limicola, and Eikelboom's type 0041 and type 021N were investigated for their ability to take up organic Substrates. A panel of six Substrates, i.e., [(sup14)C]acetate, [(sup3)H]glucose, [(sup14)C]ethanol, [(sup3)H]glycine, [(sup3)H]leucine, and [(sup3)H]oleic acid, was tested. The Uptake response was found to be very specific not only between the different filamentous types but also among filaments of the same type from different treatment plants. Interestingly, M. parvicella consistently took up only oleic acid among the tested Substrates. It is concluded that microautoradiography is a useful method for investigation of in situ Substrate Uptake by filamentous microorganisms in activated sludge.
William J. Riley - One of the best experts on this subject based on the ideXlab platform.
-
Competitor and Substrate sizes and diffusion together define enzymatic depolymerization and microbial Substrate Uptake rates
Soil Biology & Biochemistry, 2019Co-Authors: Jinyun Tang, William J. RileyAbstract:Abstract Diffusion limitations of extracellular enzymes and soluble monomers have been recognized as important mechanisms controlling soil organic matter (SOM) dynamics. Here we combine diffusion limitation with the geometric sizes of extracellular enzymes, polymer particles, monomers, and bacterial cells to derive testable relationships of SOM kinetic parameters, including (1) maximum reaction rates and (2) binding half saturation constants (also known as Substrate affinity parameters). We integrate the relevant mechanisms with the Equilibrium Chemistry Approximation (ECA) kinetics, which has been shown to reasonably represent these complex competitive interactions in soils, and then evaluate the reverse and forward Michaelis-Menten kinetics approximations under different conditions. We found: (1) due to the size contrast between larger organic polymer particles and smaller enzyme molecules, depolymerization is limited by the abundance of enzyme binding sites supplied by polymer particles, making the reverse Michaelis-Menten kinetics a better approximation to the ECA kinetics for depolymerization, and (2) due to the size contrast between larger microbial cells and smaller monomer molecules, monomer Uptake is limited by accessible microbial cell transporters, making the forward Michaelis-Menten kinetics a better approximation to ECA kinetics for microbial monomer Substrate Uptake. These results may explain conflicting applications in the literature associated with using reverse and forward Michaelis-Menten kinetics to represent SOM dynamics. Further, the size contrast between litter particles and extracellular enzymes suggests that litter fragmentation by soil fauna and fungi is an important process to be included in models of organic matter decomposition and challenges soil enzyme assays to accurately measure enzyme abundances in order to properly derive the kinetic parameters.
-
a total quasi steady state formulation of Substrate Uptake kinetics in complex networks and an example application to microbial litter decomposition
Biogeosciences, 2013Co-Authors: Jinyun Tang, William J. RileyAbstract:We demonstrate that Substrate Uptake kinetics in any consumer–Substrate network subject to the total quasi-steady-state assumption can be formulated as an equilibrium chemistry (EC) problem. If the consumer-Substrate complexes equilibrate much faster than other metabolic processes, then the relationships between consumers, Substrates, and consumer-Substrate complexes are in quasi-equilibrium and the change of a given total Substrate (free plus consumer-bounded) is determined by the degradation of all its consumer-Substrate complexes. In this EC formulation, the corresponding equilibrium reaction constants are the conventional Michaelis–Menten (MM) Substrate affinity constants. When all of the elements in a given network are either consumer or Substrate (but not both), we derived a first-order accurate EC approximation (ECA). The ECA kinetics is compatible with almost every existing extension of MM kinetics. In particular, for microbial organic matter decomposition modeling, ECA kinetics explicitly predicts a specific microbe's Uptake for a specific Substrate as a function of the microbe's affinity for the Substrate, other microbes' affinity for the Substrate, and the shielding effect on Substrate Uptake by environmental factors, such as mineral surface adsorption. By taking the EC solution as a reference, we evaluated MM and ECA kinetics for their abilities to represent several differently configured enzyme-Substrate reaction networks. In applying the ECA and MM kinetics to microbial models of different complexities, we found (i) both the ECA and MM kinetics accurately reproduced the EC solution when multiple microbes are competing for a single Substrate; (ii) ECA outperformed MM kinetics in reproducing the EC solution when a single microbe is feeding on multiple Substrates; (iii) the MM kinetics failed, while the ECA kinetics succeeded, in reproducing the EC solution when multiple consumers (i.e., microbes and mineral surfaces) were competing for multiple Substrates. We then applied the EC and ECA kinetics to a guild based C-only microbial litter decomposition model and found that both approaches successfully simulated the commonly observed (i) two-phase temporal evolution of the decomposition dynamics; (ii) final asymptotic convergence of the lignocellulose index to a constant that depends on initial litter chemistry and microbial community structure; and (iii) microbial biomass proportion of total organic biomass (litter plus microbes). In contrast, the MM kinetics failed to realistically predict these metrics. We therefore conclude that the ECA kinetics are more robust than the MM kinetics in representing complex microbial, C Substrate, and mineral surface interactions. Finally, we discuss how these concepts can be applied to other consumer–Substrate networks.
Joost J. F. P. Luiken - One of the best experts on this subject based on the ideXlab platform.
-
PS9 - 41. Translocation of Substrate transporters glut4 and cd36 to the sarcolemma and subsequent activation to increase Substrate Uptake are separate events
Nederlands Tijdschrift voor Diabetologie, 2012Co-Authors: Yeliz Angin, Robert W. Schwenk, Reyhan N. Unal, Benoit-gilles Kerfant, Dietbert Neumann, Jan F. C. Glatz, Joost J. F. P. LuikenAbstract:Myocardial glucose and long-chain fatty acid Uptake are regulated by specific membrane transport proteins, i.e., GLUT4 and CD36, respectively. Upon hormonal (insulin) or mechanical stimuli (muscle contraction) GLUT4 and CD36 move from endosomal stores to the plasma membrane to facilitate Substrate Uptake. Contraction-mediated Substrate Uptake is known to require AMP-dependent protein kinase (AMPK) activation.
-
cardiac Substrate Uptake and metabolism in obesity and type 2 diabetes role of sarcolemmal Substrate transporters
Molecular and Cellular Biochemistry, 2007Co-Authors: Susan L Coort, Jan F. C. Glatz, Joost J. F. P. Luiken, Arend Bonen, Ger J Van Der VusseAbstract:Cardiovascular disease is the primary cause of death in obesity and type-2 diabetes mellitus (T2DM). Alterations in Substrate metabolism are believed to be involved in the development of both cardiac dysfunction and insulin resistance in these conditions. Under physiological circumstances the heart utilizes predominantly long-chain fatty acids (LCFAs) (60–70%), with the remainder covered by carbohydrates, i.e., glucose (20%) and lactate (10%). The cellular Uptake of both LCFA and glucose is regulated by the sarcolemmal amount of specific transport proteins, i.e., fatty acid translocase (FAT)/CD36 and GLUT4, respectively. These transport proteins are not only present at the sarcolemma, but also in intracellular storage compartments. Both an increased workload and the hormone insulin induce translocation of FAT/CD36 and GLUT4 to the sarcolemma. In this review, recent findings on the insulin and contraction signalling pathways involved in Substrate Uptake and utilization by cardiac myocytes under physiological conditions are discussed. New insights in alterations in Substrate Uptake and utilization during insulin resistance and its progression towards T2DM suggest a pivotal role for Substrate transporters. During the development of obesity towards T2DM alterations in cardiac lipid homeostasis were found to precede alterations in glucose homeostasis. In the early stages of T2DM, relocation of FAT/CD36 to the sarcolemma is associated with the myocardial accumulation of triacylglycerols (TAGs) eventually leading to an impaired insulin-stimulated GLUT4-translocation. These novel insights may result in new strategies for the prevention of development of cardiac dysfunction and insulin resistance in obesity and T2DM.
-
signalling components involved in contraction inducible Substrate Uptake into cardiac myocytes
The Proceedings of the Nutrition Society, 2004Co-Authors: Joost J. F. P. Luiken, Susan L Coort, Arend Bonen, Debby P Y Koonen, Jan F. C. GlatzAbstract:Glucose and long-chain fatty acids (LCFA) are two major Substrates used by heart and skeletal muscle to support contractile activity. In quiescent cardiac myocytes a substantial portion of the glucose transporter GLUT4 and the putative LCFA transporter fatty acid translocase (FAT)/CD36 are stored in intracellular compartments. Induction of cellular contraction by electrical stimulation results in enhanced Uptake of both glucose and LCFA through translocation of GLUT4 and FAT/CD36 respectively to the sarcolemma. The involvement of protein kinase A, AMP-activated protein kinase (AMPK), protein kinase C (PKC) isoforms and the extracellular signal-regulated kinases was evaluated in cardiac myocytes as candidate signalling enzymes involved in recruiting these transporters in response to contraction. The collected evidence excluded the involvement of PKA and implicated an important role for AMPK and for one (or more) PKC isoform(s) in contraction-induced translocation of both GLUT4 and FAT/CD36. The unravelling of further components along this contraction pathway can provide valuable information on the coordinated regulation of the Uptake of glucose and of LCFA by an increase in mechanical activity of heart and skeletal muscle.
-
giant membrane vesicles as a model to study cellular Substrate Uptake dissected from metabolism
Molecular and Cellular Biochemistry, 2002Co-Authors: Debby P Y Koonen, Arend Bonen, Will A Coumans, Yoga Arumugam, J F C Glatz, Joost J. F. P. LuikenAbstract:In order to use giant vesicles for Substrate Uptake studies in metabolically important tissues, we characterized giant vesicles isolated from heart, liver, skeletal muscle and adipose tissue. We investigated which cell types and which plasma membrane regions are involved in giant vesicle formation and we examined the presence of transporters for metabolic Substrates. Analysis of giant vesicles with markers specific for distinct cell types and distinct domains of the plasma membrane reveals that the plasma membrane of parenchymal cells, but not endothelial cells, are the source of the vesicle membranes. In addition, plasma membrane regions enriched in caveolae and involved in docking of recycling vesicles from the endosomal compartment are retained in giant vesicles, indicating that KCl-induced alterations in recycling processes are involved in giant vesicle formation. Giant vesicles contain vesicular lumen consisting of the soluble constituents of the cytoplasm including, fatty-acid binding proteins. Furthermore, giant vesicles isolated from heart, liver, skeletal muscle and adipose tissue are similar in size (10–15 μm) and shape and do not contain subcellular organelles, providing the advantage that Substrate fluxes in the different organs can be studied independently of the surface/volume ratio but most importantly in the absence of intracellular metabolism.
Fanfan Zhou - One of the best experts on this subject based on the ideXlab platform.
-
The role of solute carrier (SLC) transporters in actinomycin D pharmacokinetics in paediatric cancer patients
European Journal of Clinical Pharmacology, 2018Co-Authors: Gareth J Veal, Fanfan Zhou, Alan V BoddyAbstract:Background Actinomycin D is used for treatment of paediatric cancers; however, a large inter-patient pharmacokinetic (PK) variability and hepatotoxicity are significant limitations to its use and warrant further investigation. Elimination of actinomycin D may be mediated by transporters, as the drug does not seem to undergo significant metabolism. We investigated the role of solute carrier (SLC) transporters in actinomycin D PK. Methods Fourteen key SLCs were screened through probe Substrate Uptake inhibition by actinomycin D in HEK293 cells. Uptake of actinomycin D was further studied in candidate SLCs by measuring intracellular actinomycin D using a validated LCMS assay. Pharmacogenetic analysis was conducted for 60 patients (Clinical trial: NCT00900354), who were genotyped for SNPs for OAT4 and PEPT2. Results OAT4, OCT2, OCT3 and PEPT2 showed significantly lower probe Substrate Uptake (mean ± SD 75.0 ± 3.5% ( p
-
the inhibitory effects of eighteen front line antibiotics on the Substrate Uptake mediated by human organic anion cation transporters organic anion transporting polypeptides and oligopeptide transporters in in vitro models
European Journal of Pharmaceutical Sciences, 2018Co-Authors: Xiaoxi Lu, Ting Chan, Tony Velkov, Qi Tony Zhou, Jian Li, Hakkim Chan, Fanfan ZhouAbstract:Human Organic anion/cation transporters (OATs/OCTs), Organic anion transporting polypeptides (OATPs) and proton-coupled Oligopeptide transporters (PepTs) are important membrane transporters responsible of the cellular influx of drugs in many human key tissues. Inhibitor(s) impacting on the cellular Uptake of transporter drug Substrates is one of the primary causes of drug-drug interactions that lead to unsatisfied therapeutic outcomes and/or unwanted side effects. In the current study, we selected eighteen antibiotic agents used in infectious disease treatment and comprehensively evaluated their inhibitory effects on the Substrate Uptake mediated through the essential OATs/OCTs, OATPs and PepTs isoforms. Transport functional assay, dose-response curve and kinetic analysis were performed on the HEK293 cells over-expressing each of these transporter genes. Our data revealed that nitrofurantoin, sulfadiazine and metronidazole significantly inhibited the transport activity of OAT3 (IC50 values of 6.23±1.33μM, 6.65±1.30μM and 6.51±0.99μM; Ki values of 5.86μM, 3.98μM and 6.48μM, respectively). Trimethoprim and ciprofloxacin potently decreased the Substrate Uptake mediated via OATP1A2 (IC50 values of 9.35±1.10μM and 9.25±1.18μM; Ki values of 8.19μM and 7.64μM, respectively). In addition, these antibiotic agents consistently decreased methotrexate influx via OAT3 and OATP1A2. In summary, our study is the first to show that nitrofurantoin, sulfadiazine and metronidazole are potent inhibitors of OAT3 and trimethoprim is a novel inhibitor of OATP1A2. Our study also provides new evidence for the drug-drug interactions of ciprofloxacin with OATP1A2 drug Substrates like methotrexate. Therefore, precautions are required when co-administering these antibiotics with OAT3 or OATP1A2 drug Substrates.
-
The inhibitory effects of eighteen front-line antibiotics on the Substrate Uptake mediated by human Organic anion/cation transporters, Organic anion transporting polypeptides and Oligopeptide transporters in in vitro models.
European Journal of Pharmaceutical Sciences, 2018Co-Authors: Xiaoxi Lu, Ting Chan, Tony Velkov, Qi Tony Zhou, Jian Li, Hakkim Chan, Fanfan ZhouAbstract:Abstract Human Organic anion/cation transporters (OATs/OCTs), Organic anion transporting polypeptides (OATPs) and proton-coupled Oligopeptide transporters (PepTs) are important membrane transporters responsible of the cellular influx of drugs in many human key tissues. Inhibitor(s) impacting on the cellular Uptake of transporter drug Substrates is one of the primary causes of drug-drug interactions that lead to unsatisfied therapeutic outcomes and/or unwanted side effects. In the current study, we selected eighteen antibiotic agents used in infectious disease treatment and comprehensively evaluated their inhibitory effects on the Substrate Uptake mediated through the essential OATs/OCTs, OATPs and PepTs isoforms. Transport functional assay, dose-response curve and kinetic analysis were performed on the HEK293 cells over-expressing each of these transporter genes. Our data revealed that nitrofurantoin, sulfadiazine and metronidazole significantly inhibited the transport activity of OAT3 (IC50 values of 6.23 ± 1.33 μM, 6.65 ± 1.30 μM and 6.51 ± 0.99 μM; Ki values of 5.86 μM, 3.98 μM and 6.48 μM, respectively). Trimethoprim and ciprofloxacin potently decreased the Substrate Uptake mediated via OATP1A2 (IC50 values of 9.35 ± 1.10 μM and 9.25 ± 1.18 μM; Ki values of 8.19 μM and 7.64 μM, respectively). In addition, these antibiotic agents consistently decreased methotrexate influx via OAT3 and OATP1A2. In summary, our study is the first to show that nitrofurantoin, sulfadiazine and metronidazole are potent inhibitors of OAT3 and trimethoprim is a novel inhibitor of OATP1A2. Our study also provides new evidence for the drug-drug interactions of ciprofloxacin with OATP1A2 drug Substrates like methotrexate. Therefore, precautions are required when co-administering these antibiotics with OAT3 or OATP1A2 drug Substrates.
Ivet Bahar - One of the best experts on this subject based on the ideXlab platform.
-
microseconds simulations reveal a new sodium binding site and the mechanism of sodium coupled Substrate Uptake by leut
Journal of Biological Chemistry, 2015Co-Authors: Elia Zomot, Ivet BaharAbstract:The bacterial sodium-coupled leucine/alanine transporter LeuT is broadly used as a model system for studying the transport mechanism of neurotransmitters because of its structural and functional homology to mammalian transporters such as serotonin, dopamine, or norepinephrine transporters, and because of the resolution of its structure in different states. Although the binding sites (S1 for Substrate, and Na1 and Na2 for two co-transported sodium ions) have been resolved, we still lack a mechanistic understanding of coupled Na+- and Substrate-binding events. We present here results from extensive (>20 μs) unbiased molecular dynamics simulations generated using the latest computing technology. Simulations show that sodium binds initially the Na1 site, but not Na2, and, consistently, sodium unbinding/escape to the extracellular (EC) region first takes place at Na2, succeeded by Na1. Na2 diffusion back to the EC medium requires prior dissociation of Substrate from S1. Significantly, Na+ binding (and unbinding) consistently involves a transient binding to a newly discovered site, Na1″, near S1, as an intermediate state. A robust sequence of Substrate Uptake events coupled to sodium bindings and translocations between those sites assisted by hydration emerges from the simulations: (i) bindings of a first Na+ to Na1″, translocation to Na1, a second Na+ to vacated Na1″ and then to Na2, and Substrate to S1; (ii) rotation of Phe253 aromatic group to seclude the Substrate from the EC region; and (iii) concerted tilting of TM1b and TM6a toward TM3 and TM8 to close the EC vestibule.
