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1.
Proc Natl Acad Sci U S A ; 117(28): 16626-16637, 2020 07 14.
Artigo em Inglês | MEDLINE | ID: mdl-32601236

RESUMO

Neuronal activity leads to an increase in local cerebral blood flow (CBF) to allow adequate supply of oxygen and nutrients to active neurons, a process termed neurovascular coupling (NVC). We have previously shown that capillary endothelial cell (cEC) inwardly rectifying K+ (Kir) channels can sense neuronally evoked increases in interstitial K+ and induce rapid and robust dilations of upstream parenchymal arterioles, suggesting a key role of cECs in NVC. The requirements of this signal conduction remain elusive. Here, we utilize mathematical modeling to investigate how small outward currents in stimulated cECs can elicit physiologically relevant spread of vasodilatory signals within the highly interconnected brain microvascular network to increase local CBF. Our model shows that the Kir channel can act as an "on-off" switch in cECs to hyperpolarize the cell membrane as extracellular K+ increases. A local hyperpolarization can be amplified by the voltage-dependent activation of Kir in neighboring cECs. Sufficient Kir density enables robust amplification of the hyperpolarizing stimulus and produces responses that resemble action potentials in excitable cells. This Kir-mediated excitability can remain localized in the stimulated region or regeneratively propagate over significant distances in the microvascular network, thus dramatically increasing the efficacy of K+ for eliciting local hyperemia. Modeling results show how changes in cEC transmembrane current densities and gap junctional resistances can affect K+-mediated NVC and suggest a key role for Kir as a sensor of neuronal activity and an amplifier of retrograde electrical signaling in the cerebral vasculature.


Assuntos
Neurônios/metabolismo , Acoplamento Neurovascular , Canais de Potássio Corretores do Fluxo de Internalização/metabolismo , Potássio/metabolismo , Animais , Encéfalo/irrigação sanguínea , Encéfalo/metabolismo , Circulação Cerebrovascular , Células Endoteliais/química , Células Endoteliais/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Modelos Biológicos , Neurônios/química , Potássio/química , Canais de Potássio Corretores do Fluxo de Internalização/química , Canais de Potássio Corretores do Fluxo de Internalização/genética , Transdução de Sinais , Canais de Cátion TRPV/química , Canais de Cátion TRPV/genética , Canais de Cátion TRPV/metabolismo
2.
PLoS One ; 15(7): e0236634, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32706842

RESUMO

Potassium (K) input is essential for the improvement of soil fertility in agricultural systems. However, organic amendment may differ from mineral K fertilization with respect to modifying the soil K transformation among different fractions, affecting soil K availability. We conducted a 60-day lab incubation experiment to evaluate the response of soil K dynamics and availability in various fractions with a view to simulating crop residue return and chemical K fertilization in an Anthrosol of northwest China. The tested soil was divided into two main groups, no K fertilization (K0) and K fertilization (K1), each of which was subjected to four straw addition regimes: no straw addition (Control), wheat straw addition (WS), maize straw addition (MS), and both wheat straw and maize straw addition (WS+MS). Soil K levels in the available (AK) and non-exchangeable (NEK) fractions were both significantly increased after K addition, following the order of K>WS>MS. Fertilizer K was the most efficient K source, demonstrating a 72.9% efficiency in increasing soil AK, while wheat and maize straw exhibited efficiencies of 47.1% and 39.3%, respectively. Furthermore, K fertilization and wheat and maize straw addition increased the soil AK in a cumulative manner when used in combination. The mobility factor (MF) and reduced partition index (IR) of soil K were used to quantitate the comprehensive soil K mobility and stability, respectively. Positive relationships were observed between the MF and all relatively available fractions of soil K, whereas the IR value of soil K correlated negatively with both MF and all available fractions of soil K. In conclusion, straw amendment could be inferior to mineral K fertilization in improving soil K availability when they were almost equal in the net K input. Crop straw return coupled with K fertilization can be a promising strategy for improving both soil K availability and cycling in soil-plant systems.


Assuntos
Agricultura , Potássio/química , Solo/química , Triticum/metabolismo , Zea mays/metabolismo , China , Fertilizantes/análise , Potássio/metabolismo , Análise de Componente Principal , Triticum/química , Zea mays/química
3.
Food Chem ; 333: 127493, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-32659659

RESUMO

The effects of the addition of salt ions and molecular weights (Mw) of CH on Mesona chinensis polysaccharide (MCP)-chitosan (CH) hydrogel were investigated. Result indicated both low concentration of monovalent salt ions (Na+ and K+), divalent cations (Ca2+) and oxoanions (SO42-) could promote the gel properties of MCP-CH hydrogel. The Mw of CH has huge impact on the formation and properties of hydrogel. Combining the relationship between rheology and structural, monovalent salt ions such as Na+ and K+ affect gel formation and its properties by influencing electrostatic interaction and chain conformation. Both divalent cations (Ca2+) and oxoanions (SO42-) facilitated the formation of gel networks via electrostatic interaction, coordination bonds and hydrogen bonds. Moreover, Mw of CH influenced formation and texture of MCP-CH hydrogel via affecting the conformation of CH molecular chain. These findings will provide a few theoretical bases to understand the formation mechanism of MCP-CH hydrogel.


Assuntos
Quitosana/química , Hidrogéis/química , Lamiaceae/química , Extratos Vegetais/química , Polieletrólitos/química , Sais/química , Ânions/química , Cálcio/química , Hidrogéis/síntese química , Peso Molecular , Polissacarídeos/química , Potássio/química , Reologia , Sódio/química
4.
Nat Commun ; 11(1): 3024, 2020 06 15.
Artigo em Inglês | MEDLINE | ID: mdl-32541684

RESUMO

The canonical mechanistic model explaining potassium channel gating is of a conformational change that alternately dilates and constricts a collar-like intracellular entrance to the pore. It is based on the premise that K+ ions maintain a complete hydration shell while passing between the transmembrane cavity and cytosol, which must be accommodated. To put the canonical model to the test, we locked the conformation of a Kir K+ channel to prevent widening of the narrow collar. Unexpectedly, conduction was unimpaired in the locked channels. In parallel, we employed all-atom molecular dynamics to simulate K+ ions moving along the conduction pathway between the lower cavity and cytosol. During simulations, the constriction did not significantly widen. Instead, transient loss of some water molecules facilitated K+ permeation through the collar. The low free energy barrier to partial dehydration in the absence of conformational change indicates Kir channels are not gated by the canonical mechanism.


Assuntos
Canais de Potássio Corretores do Fluxo de Internalização Acoplados a Proteínas G/metabolismo , Potássio/metabolismo , Citosol/química , Citosol/metabolismo , Condutividade Elétrica , Impedância Elétrica , Canais de Potássio Corretores do Fluxo de Internalização Acoplados a Proteínas G/química , Canais de Potássio Corretores do Fluxo de Internalização Acoplados a Proteínas G/genética , Humanos , Transporte de Íons , Íons/química , Íons/metabolismo , Simulação de Dinâmica Molecular , Potássio/química , Conformação Proteica , Água/metabolismo
5.
Acta Crystallogr D Struct Biol ; 76(Pt 4): 326-331, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32254056

RESUMO

The study of ion channels dates back to the 1950s and the groundbreaking electrophysiology work of Hodgin and Huxley, who used giant squid axons to probe how action potentials in neurons were initiated and propagated. More recently, several experiments using different structural biology techniques and approaches have been conducted to try to understand how potassium ions permeate through the selectivity filter of potassium ion channels. Two mechanisms of permeation have been proposed, and each of the two mechanisms is supported by different experiments. The key structural biology experiments conducted so far to try to understand how ion permeation takes place in potassium ion channels are reviewed and discussed. Protein crystallography has made, and continues to make, key contributions in this field, often through the use of anomalous scattering. Other structural biology techniques used to study the contents of the selectivity filter include solid-state nuclear magnetic resonance and two-dimensional infrared spectroscopy, both of which make clever use of isotopic labeling techniques, while molecular-dynamics simulations of ion flow through the selectivity filter have been enabled by the growing number of potassium ion channel structures deposited in the Protein Data Bank.


Assuntos
Simulação de Dinâmica Molecular , Canais de Potássio/química , Potássio/química , Cristalografia por Raios X , Marcação por Isótopo , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular , Estrutura Terciária de Proteína , Espalhamento de Radiação , Espectrofotometria Infravermelho
6.
J Chromatogr A ; 1622: 461095, 2020 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-32334852

RESUMO

A two-membrane electrodialytic carbonate eluent generator (EDG) for ion chromatography (IC) is described. It is in a sandwich-like configuration, in which the central eluent channel is spatially isolated from two outer regenerant channels by stacked cation exchange membranes (CEMs) and anion exchange membranes (AEMs). A platinum screen electrode is placed in each of two outer regenerant channels. The electrode at the CEMs side is set as an anode with respect to the electrode at the AEMs side being cathode. Potassium carbonate and/or bicarbonate solution is pumped into the regenerant channel as feed solution. The electromigration of carbonate and/or bicarbonate and potassium from feed solution respectively through AEMs and CEMs will form a gas-free eluent. With this configuration, ion transport behavior through AEMs was explored. The device demonstrated good reproducibility, as indicated by the relative standard deviation of retention time of less than 0.08%.


Assuntos
Carbonatos , Técnicas de Química Analítica , Cromatografia por Troca Iônica , Bicarbonatos/química , Carbonatos/química , Cátions/química , Técnicas de Química Analítica/instrumentação , Técnicas de Química Analítica/métodos , Cromatografia por Troca Iônica/instrumentação , Eletrodos , Potássio/química , Reprodutibilidade dos Testes
7.
PLoS One ; 15(3): e0230178, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32187213

RESUMO

The Olsen phosphorus (Olsen-P) concentration of soil is generally a good indicator for estimating the bioavailability of P and environmental risk in soils. To maintain soil Olsen-P at adequate levels for crop growth and environmental sustainability, the relationship between soil Olsen-P and the P budget (the P input minus the output) as well as the variations of soil Olsen-P and P budget were investigated from three long-term (22 years) experiments in China. Five treatments were selected: (1) unfertilized control (CK); (2) nitrogen and potassium (NK); (3) nitrogen, phosphorous, and potassium (NPK); (4) nitrogen, phosphorous, potassium and straw; (5) nitrogen, phosphorous, potassium and manure. The results showed that without P fertilizers (CK, NK), there was a soil P deficit of 75-640 kg ha-1, and the lowest P deficit (mean of CK and NK) was in Eutric Cambisol. Soil Olsen-P decreased by 0.11-0.39 mg kg-1 year-1 in the order of Luvic Phaeozems > Eutric Cambisol > Calcaric Cambisol. Soil Olsen-P and the P deficit had a significantly (P<0.01) positive linear relationship. For every 100 kg of P ha-1 of deficit, soil Olsen-P decreased by 0.44-9.19 mg kg-1 in the order of Eutric Cambisol > Luvic Phaeozems > Calcaric Cambisol. Under the P fertilizer treatments (NPK, NPKS, and NPKM), soil Olsen-P showed an obvious surplus (except the NPK and NPKS in Luvic Phaeozems) of 122-2190 kg ha-1, and the largest P surplus was found under the NPKM treatment at each site. The relation between soil Olsen-P and the experimental years could be simulated using quadratic equation of one unknown in Calcaric Cambisol for the lower P input after 14 years of fertilization. And soil Olsen-P increased by 1.30-7.69 mg kg-1 year-1 in the order of Luvic Phaeozems > Eutric Cambisol. The relation between soil Olsen-P and the P surplus could be simulated by a simple linear equation except under NPK and NPKS in Luvic Phaeozems. With 100 kg ha-1 P surplus, soil Olsen-P increased by 3.24-7.27 mg kg-1 in the order of Calcaric Cambisol (6.42 mg kg-1) > Eutric Cambisol (3.24 mg kg-1). In addition, the change in soil Olsen-P with a 100 kg P ha-1 surplus (soil Olsen-P efficiency) was affected by the soil organic matter (SOM), pH, and CaCO3 content, etc. In the practice of fertilization, it's not necessary to increase the amount of P fertilizers, farmers should take measure to solve the local problem, for adjust the soil pH of Eutric Cambisol and Calcaric Cambisol, and apply more nitrogen in Luvic Phaeozems. In the area of serious soil P surplus, it is encouraged to stop applying P fertilizers for a few years to take advantage of soil accumulated P and make the high Olsen-P content decrease to a reasonable level.


Assuntos
Fósforo/química , Potássio/química , Agricultura/métodos , China , Produtos Agrícolas/química , Fazendeiros , Fertilizantes , Esterco/análise , Nitrogênio/química , Solo
8.
Adv Immunol ; 145: 187-241, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32081198

RESUMO

Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental biological processes. Especially, the transition metals iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), copper (Cu) and cobalt (Co) are crucial micronutrients known to play vital roles in metabolism as well due to their unique redox properties. Metals carry out three major functions within metalloproteins: to provide structural support, to serve as enzymatic cofactors, and to mediate electron transportation. Metal ions are also involved in the immune system from metal allergies to nutritional immunity. Within the past decade, much attention has been drawn to the roles of metal ions in the immune system, since increasing evidence has mounted to suggest that metals are critically implicated in regulating both the innate immune sensing of and the host defense against invading pathogens. The importance of ions in immunity is also evidenced by the identification of various immunodeficiencies in patients with mutations in ion channels and transporters. In addition, cancer immunotherapy has recently been conclusively demonstrated to be effective and important for future tumor treatment, although only a small percentage of cancer patients respond to immunotherapy because of inadequate immune activation. Importantly, metal ion-activated immunotherapy is becoming an effective and potential way in tumor therapy for better clinical application. Nevertheless, we are still in a primary stage of discovering the diverse immunological functions of ions and mechanistically understanding the roles of these ions in immune regulation. This review summarizes recent advances in the understanding of metal-controlled immunity. Particular emphasis is put on the mechanisms of innate immune stimulation and T cell activation by the essential metal ions like calcium (Ca2+), zinc (Zn2+), manganese (Mn2+), iron (Fe2+/Fe3+), and potassium (K+), followed by a few unessential metals, in order to draw a general diagram of metalloimmunology.


Assuntos
Imunidade Inata , Metais/metabolismo , Transdução de Sinais/imunologia , Animais , Cálcio/química , Cálcio/metabolismo , Cálcio/fisiologia , Enzimas , Humanos , Imunoterapia , Íons/química , Íons/metabolismo , Ferro/metabolismo , Ferro/fisiologia , Manganês/metabolismo , Manganês/fisiologia , Metais/química , Neoplasias/tratamento farmacológico , Neoplasias/enzimologia , Neoplasias/imunologia , Potássio/química , Potássio/metabolismo , Potássio/fisiologia , Zinco/química , Zinco/deficiência , Zinco/fisiologia
9.
PLoS One ; 15(1): e0227594, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31914170

RESUMO

The ecological environment of the Yellow River Delta is fragile, and the soil degradation in the region is serious. Therefore it is important to discern the status of the soil degradation in a timely manner for soil conservation and utilization. The study area of this study was Kenli County in the Yellow River Delta of China. First, physical and chemical data of the soil were obtained by field investigations and soil sample analyses, and the hyper-spectra of air-dried soil samples were obtained via spectrometer. Then, the soil degradation index (SDI) was constructed by the key indicators of soil degradation, including pH, SSC, OM, AN, AP, AK, and soil texture. Next, according to a cluster analysis, soil degradation was divided into the following three grades: light degradation, moderate degradation, and heavy degradation. Moreover, the spectral characteristics of soil degradation were analyzed, and an estimation model of SDI was established by multiple stepwise regression. The results showed that the overall level of reflectance spectra increased with increased degree of soil degradation, that both derivative transformation and waveband reorganization could enhance the spectral information of soil degradation, and that the correlation between SDI and the spectral parameter of (Rλ2+Rλ1)/(Rλ2-Rλ1) was the highest among all the spectral parameters studied. On this basis, the optimum estimation model of SDI was established with the correlation coefficient of 0.811. This study fully embodies the potential of hyper-spectral technology in the study of soil degradation and provides a technical reference for the rapid extraction of information from soil degradation. Additionally, the study area is typical and representative, and thus can indirectly reflect the soil degradation situation of the whole Yellow River Delta.


Assuntos
Monitoramento Ambiental/métodos , Solo/química , Análise Espectral/métodos , China , Análise por Conglomerados , Monitoramento Ambiental/estatística & dados numéricos , Concentração de Íons de Hidrogênio , Modelos Teóricos , Nitrogênio/análise , Nitrogênio/química , Fósforo/análise , Fósforo/química , Potássio/análise , Potássio/química
10.
J Phys Chem Lett ; 11(4): 1305-1309, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-31967478

RESUMO

G-Quadruplexes are formed by guanine rich DNA/RNA sequences in the presence of metal ions, which occupy the central cavity of these four-stranded structures. We show that these metal ions have a significant effect on the photogeneration and the reactivity of guanine radicals. Transient absorption experiments on G-quadruplexes formed by association of four TGGGGT strands in the presence of K+ reveal that the quantum yield of one-photon ionization at 266 nm (8.1 × 10-3) is twice as high as that determined in the presence of Na+. Replacement of Na+ with K+ also suppresses one reaction path involving deprotonated radicals, (G-H2)• → (G-H1)• tautomerization. Such behavior shows that the underlying mechanisms are governed by dynamical processes, controlled by the mobility of metal ions, which is higher for Na+ than for K+. These findings may contribute to our understanding of the ultraviolet-induced DNA damage and optimize optoelectronic devices based on four-stranded structures, beyond DNA.


Assuntos
Quadruplex G , Guanina/química , Potássio/química , Dano ao DNA/efeitos da radiação , Radicais Livres/química , Radicais Livres/metabolismo , Íons/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Fótons , Teoria Quântica , Raios Ultravioleta
11.
Molecules ; 25(2)2020 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-31963280

RESUMO

Considered to be the next generation of heat transfer fluids (HTFs), nanofluids have been receiving a growing interest over the past decade. Molten salt nanofluids have been shown to have great potential as an HTF for use in high temperature applications such as direct absorption solar collector (DAC) system. Very few studies using molten salt nanofluids as the HTF in a DAC receiver can be found in the open literature. This study aimed to develop a 3D computational fluid dynamics model of the receiver of a DAC using graphite-nanoparticle-dispersed Li2CO3-K2CO3 molten salt nanofluid to investigate the effects of design and operation parameters on receiver performance. Receiver total efficiency using Li2CO3-K2CO3 salt was compared with that using solar salt nanofluid. Spectral properties of the base fluid and nanoparticles were modeled as wavelength-dependent and the absorption of the solar radiation was modeled as a volumetric heat release in the flowing heat transfer fluid. Initial results show that the receiver efficiency increases with increasing solar concentration, decreasing nanoparticle volume fraction, and decreasing receiver length. It was also found that the Carnot efficiency increases with increasing receiver length and nanoparticle volume fraction, and decreasing solar concentration and inlet velocity. Comparative study shows that solar salt HTF could provide higher total efficiency. However, a higher operating temperature of Li2CO3-K2CO3 will allow for a greater amount of thermal energy storage for a smaller volume of liquid.


Assuntos
Carbonatos/química , Grafite/química , Carbonato de Lítio/química , Nanopartículas/química , Potássio/química , Energia Solar , Adsorção , Algoritmos , Hidrodinâmica , Modelos Teóricos , Fenômenos Físicos , Reprodutibilidade dos Testes , Soluções
12.
Nucleic Acids Res ; 48(1): 75-85, 2020 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-31777918

RESUMO

One of the major hurdles in RNAi research has been the development of safe and effective delivery systems for siRNAs. Although various chemical modifications have been proposed to improve their pharmacokinetic behaviour, their delivery to target cells and tissues presents many challenges. In this work, we implemented a receptor-targeting strategy to selectively deliver siRNAs to cancer cells using folic acid as a ligand. Folic acid is capable of binding to cell-surface folate receptors with high affinity. These receptors have become important molecular targets for cancer research as they are overexpressed in numerous cancers despite being expressed at low levels in normal tissues. Employing a post-column copper-catalyzed alkyne-azide cycloaddition (CuAAC), we report the synthesis of siRNAs bearing folic acid modifications at different positions within the sense strand. In the absence of a transfection carrier, these siRNAs were selectively taken up by cancer cells expressing folate receptors. We show that centrally modified folic acid-siRNAs display enhanced gene-silencing activity against an exogenous gene target (∼80% knockdown after 0.75 µM treatment) and low cytotoxicity. In addition, these siRNAs achieved potent dose-dependent knockdown of endogenous Bcl-2, an important anti-apoptotic gene.


Assuntos
Ácido Fólico/química , Inativação Gênica , Marcação de Genes/métodos , Proteínas Proto-Oncogênicas c-bcl-2/genética , RNA Interferente Pequeno/genética , Carbonatos/química , Sobrevivência Celular , Receptores de Folato com Âncoras de GPI/genética , Receptores de Folato com Âncoras de GPI/metabolismo , Ácido Fólico/metabolismo , Genes Reporter , Células HT29 , Células HeLa , Humanos , Luciferases/antagonistas & inibidores , Luciferases/genética , Luciferases/metabolismo , Pargilina/análogos & derivados , Pargilina/química , Potássio/química , Ligação Proteica , Proteínas Proto-Oncogênicas c-bcl-2/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , RNA Interferente Pequeno/síntese química , Transfecção
13.
Ecotoxicol Environ Saf ; 189: 109997, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31812023

RESUMO

In the current experiment, influence of NPK composition on the Cd contaminated soil-plant (Solanum nigrum L.) system as well as the phytoremediation efficiency were comprehensively studied. The composition of NPK was optimized for a sustainable phytoremediation and simultaneous agronomic technique in Cd-contaminated soil by orthogonal (L14) experiment, aimed to achieve plant productivity and maximum phytoremediation potential enhancement. Results showed that different treatments of NPK composition enhanced soil properties including saccharase, urease, catalase and acid phosphatase activities as compared to the control treatment, however, soil pH was slightly decreased by 3.64%~6.67% with different composition of NPK treatments. Plant biomass and Cd concentration in the aboveground part (stem and leaves) of S. nigrum were significantly (P < 0.05) enhanced by 14.19%~48.97% and 38.50%~127.15% as compared to control plants with the addition of NPK fertilizers having different composition. Meanwhile, with the application of NPK fertilizer root/shoot Cd ratio and translocation factor (TF) was significantly decreased, however, bioconcentration factor (BCF) was increased as compared to control. Additionally, different composition of NPK fertilizers significantly increased photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids) and soluble protein in comparison to control. The activities of antioxidant enzymes in S. nigrum including ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) were increased, while malonaldehyde (MDA) and proline contents were decreased. Principal component analysis (PCA) showed that N3P2K2 treatment had the highest comprehensive score amongst other studied treatments of NPK composition, owing to its optimal composition for the investigated soil-S. nigrum system. Moreover, it was found that optimal composition (N3P2K2) of fertilizer resulted in increase of the plant resistance to Cd and the efficiency of phytoextraction. Therefore, it is suggested to all the small-holder famers and scientific community that precise composition of NPK fertilizer should be utilized according to soil properties, environmental conditions and plant requirements under Cd-stress condition in order to achieve maximum biomass, Cd uptake efficiency as well phytoremediation potential in moderately Cd contaminated soil.


Assuntos
Biodegradação Ambiental , Cádmio/metabolismo , Fertilizantes , Poluentes do Solo/metabolismo , Solanum nigrum/metabolismo , Antioxidantes/metabolismo , Biomassa , Cádmio/análise , Carotenoides/metabolismo , Clorofila/metabolismo , Clorofila A/metabolismo , Nitrogênio/análise , Nitrogênio/química , Fósforo/análise , Fósforo/química , Folhas de Planta/metabolismo , Potássio/análise , Potássio/química , Análise de Componente Principal , Solo/química , Poluentes do Solo/análise
14.
Chemistry ; 26(2): 543-547, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31691389

RESUMO

Herein, a visible-light photochemical approach for practical helicene functionalization at very mild reaction conditions is described. The photochemical reactions allow for the regiospecific and innate late-stage functionalization of helicenes and are easily executed either through the activation of C(sp2 )-Br bonds in helicenes using K2 CO3 as inorganic base or direct C(sp2 )-H helicene bond functionalization under oxidative photoredox reaction conditions. Overall, using these transformations six different functional groups are introduced to the helicene scaffold through C-C and four different C-heteroatom bond-forming reactions.


Assuntos
Luz , Compostos Policíclicos/química , Carbonatos/química , Catálise , Oxirredução , Potássio/química , Teoria Quântica
15.
Food Chem ; 306: 125578, 2020 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-31622835

RESUMO

Oleosomes are storage vehicles of TAGs in plant seeds. They are protected with a phospholipid-protein monolayer and extracted with alkaline aqueous media; however, pH adjustment intensifies the extraction process. Therefore, the aim of this work was to investigate the extraction mechanism of rapeseed oleosomes at pH 7 and at the presence of monovalent and divalent cations (Na+, K+, Mg2+, and Ca+2). The oleosome yield at pH 9.5 was 64 wt%, while the yield at pH 7 with H2O was just 43 wt.%. The presence of cations at pH 7, significantly enhanced the yield, with K+ giving the highest yield (64 wt.%). The cations affected the oleosome interface and their interactions. The presence of monovalent cations resulted in aggregation and minor coalescence, while divalent cations resulted in extensive coalescence. These results help to understand the interactions of oleosomes in their native matrix and design simple extraction processes at neutral conditions.


Assuntos
Brassica/química , Cálcio/química , Magnésio/química , Extratos Vegetais/química , Potássio/química , Sódio/química , Cátions Bivalentes/química , Cátions Monovalentes/química , Concentração de Íons de Hidrogênio , Gotículas Lipídicas , Sementes/química , Água
16.
Nucleic Acids Res ; 48(3): 1406-1422, 2020 02 20.
Artigo em Inglês | MEDLINE | ID: mdl-31863586

RESUMO

Recent advances in gene editing have been enabled by programmable nucleases such as transcription activator-like effector nucleases (TALENs) and CRISPR-Cas9. However, several open questions remain regarding the molecular machinery in these systems, including fundamental search and binding behavior as well as role of off-target binding and specificity. In order to achieve efficient and specific cleavage at target sites, a high degree of target site discrimination must be demonstrated for gene editing applications. In this work, we studied the binding affinity and specificity for a series of TALE proteins under a variety of solution conditions using in vitro fluorescence methods and molecular dynamics (MD) simulations. Remarkably, we identified that TALEs demonstrate high sequence specificity only upon addition of small amounts of certain divalent cations (Mg2+, Ca2+). However, under purely monovalent salt conditions (K+, Na+), TALEs bind to specific and non-specific DNA with nearly equal affinity. Divalent cations preferentially bind to DNA over monovalent cations, which attenuates non-specific interactions between TALEs and DNA and further stabilizes specific interactions. Overall, these results uncover new mechanistic insights into the binding action of TALEs and further provide potential avenues for engineering and application of TALE- or TALEN-based systems for genome editing and regulation.


Assuntos
Cálcio/química , Cátions Bivalentes/química , DNA/química , Magnésio/química , Nucleases dos Efetores Semelhantes a Ativadores de Transcrição/química , Sistemas CRISPR-Cas/genética , Proteínas de Ligação a DNA/química , Edição de Genes , Potássio/química , Ligação Proteica , Sódio/química , Soluções/química , Nucleases dos Efetores Semelhantes a Ativadores de Transcrição/metabolismo
17.
Chemosphere ; 245: 125561, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31862550

RESUMO

In Campine region in Flanders (Belgium) there are contaminated sites with Cd and Zn due to atmospheric deposition from industry. Flanders is also known for its large surpluses of nitrogen and phosphorous coming from intense livestock production. To solve both issues, the potential of biochar to sorb metals and nutrients was investigated. Experiments were conducted to examine whether biochar could reduce the leaching of nutrients (K, P and S) and metals (Cd and Zn) into the soil solution. Most biochars caused an increase in pH of approximately 1 unit which is often the main driver of the metal immobilization. Nutrient concentrations in the leachate of soil amended with oak-based biochar were lower compared to the blank soil. For the other amendments, however, the results were higher due to the nutrients leached from the applied products. The result of this experiment emphasize the potential of biochar to immobilize nutrients and metals in soil water systems, thus keeping the nutrients longer available for the plant and reducing the metal toxicity. However, the amount of metals immobilized was lower than expected. Further research is required to determine whether biochar from livestock products could act as a slow release fertilizer.


Assuntos
Carvão Vegetal/química , Metais Pesados/química , Poluentes do Solo/química , Bélgica , Cádmio/química , Poluição Ambiental , Metais Pesados/análise , Nitrogênio , Nutrientes , Fósforo , Potássio/química , Solo , Poluentes do Solo/análise , Água , Zinco/análise , Zinco/química
18.
Int J Mol Sci ; 20(24)2019 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-31817793

RESUMO

Electron transfer induced decomposition mechanism of nitroimidazole and a selection of analogue molecules in collisions with neutral potassium (K) atoms from 10 to 1000 eV have been thoroughly investigated. In this laboratory collision regime, the formation of negative ions was time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant anions have been assigned to the parent molecule and the nitrogen oxide anion (NO2-) and the electron transfer mechanisms are comprehensively discussed. This work focuses on the analysis of all fragment anions produced and it is complementary of our recent work on selective hydrogen loss from the transient negative ions produced in these collisions. Ab initio theoretical calculations were performed for 4-nitroimidazole (4NI), 2-nitroimidazole (2NI), 1-methyl-4- (Me4NI) and 1-methyl-5-nitroimidazole (Me5NI), and imidazole (IMI) in the presence of a potassium atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.


Assuntos
Nitroimidazóis/química , Potássio/química , Espectrometria de Massas
19.
Elife ; 82019 12 23.
Artigo em Inglês | MEDLINE | ID: mdl-31868587

RESUMO

RCK domains regulate the activity of K+ channels and transporters in eukaryotic and prokaryotic organisms by responding to ions or nucleotides. The mechanisms of RCK activation by Ca2+ in the eukaryotic BK and bacterial MthK K+ channels are well understood. However, the molecular details of activation in nucleotide-dependent RCK domains are not clear. Through a functional and structural analysis of the mechanism of ATP activation in KtrA, a RCK domain from the B. subtilis KtrAB cation channel, we have found that activation by nucleotide requires binding of cations to an intra-dimer interface site in the RCK dimer. In particular, divalent cations are coordinated by the γ-phosphates of bound-ATP, tethering the two subunits and stabilizing the active state conformation. Strikingly, the binding site residues are highly conserved in many different nucleotide-dependent RCK domains, indicating that divalent cations are a general cofactor in the regulatory mechanism of many nucleotide-dependent RCK domains.


Assuntos
Proteínas de Bactérias/química , Proteínas de Transporte de Cátions/química , Nucleotídeos/química , Conformação Proteica , Trifosfato de Adenosina/química , Bacillus subtilis/química , Bacillus subtilis/genética , Proteínas de Bactérias/genética , Proteínas de Bactérias/ultraestrutura , Sítios de Ligação/genética , Cálcio/metabolismo , Proteínas de Transporte de Cátions/genética , Proteínas de Transporte de Cátions/ultraestrutura , Cátions/química , Cristalografia por Raios X , Canal de Potássio Kv1.6/química , Canal de Potássio Kv1.6/ultraestrutura , Nucleotídeos/genética , Potássio/química , Potássio/metabolismo , Canais de Potássio/química , Canais de Potássio/genética , Canais de Potássio/ultraestrutura , Domínios Proteicos/genética , Estrutura Terciária de Proteína , Proteínas Ribossômicas
20.
Biochemistry (Mosc) ; 84(11): 1280-1295, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31760918

RESUMO

Maintenance of non-equilibrium Na+ and K+ distribution between cytoplasm and extracellular medium suggests existence of sensors responding with conformational transitions to the changes of these monovalent cations' intracellular concentration. Molecular nature of monovalent cation sensors has been established in Na,K-ATPase, G-protein-coupled receptors, and heat shock proteins structural studies. Recently, it was found that changes in Na+ and K+ intracellular concentration are the key factors in the transcription and translation control, respectively. In this review, we summarize results of these studies and discuss physiological and pathophysiological significance of Na+i,K+i-dependent gene expression regulation mechanism.


Assuntos
Potássio/metabolismo , ATPase Trocadora de Sódio-Potássio/metabolismo , Sódio/metabolismo , Animais , Cátions Monovalentes/química , Citoplasma/metabolismo , Proteínas de Choque Térmico/metabolismo , Potássio/química , Biossíntese de Proteínas , Sódio/química , Transcrição Genética
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