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1.
Life Sci ; 264: 118639, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-33141041

RESUMO

AIMS: This work was achieved to obtain the optimum culture conditions of the thermostable alpha-amylase produced by thermophilic Bacillus licheniformis SO-B3. Furthermore, the α-amylase was purified and then characterized, and also its kinetic parameters were determined. MATERIALS AND METHODS: A new thermotolerant bacteria called Bacillus licheniformis SO-B3 employed in this work was isolated from a sample of thermal spring mud in Sirnak (Meyremderesi). Several parameters such as the impact of temperature, time, and pH on enzyme production were examined. Thin-Layer Chromatography (TLC) was employed to analyze the end-products of soluble starch hydrolysis, and the utilization of purified α-amylase in the clarification of unripe apple juices was studied. KEY FINDINGS: The highest enzyme production conditions were determined as 35 °C, 36th hour, and pH 7.0. Thermostable α-amylase was purified by 70% ammonium sulfate precipitation, DEAE-cellulose ion-exchange chromatography, and dialysis, with a 51-purification fold and 30% yield recovery. The Km and Vmax values for this enzyme were 0.004 mM and 3.07 µmol min-1 at 70 °C, respectively. The α-amylase's molecular weight was found as 74 kDa. In addition, α-amylase showed a good degradation rate for raw starch. SIGNIFICANCE: It was hypothesized that Bacillus licheniformis SO-B3 could be used as an α-amylase source. These findings displayed that purified enzyme could be utilized in fruit juice industries for clarification of apple juice and raw starch hydrolyzing.


Assuntos
Bacillus licheniformis/metabolismo , alfa-Amilases/biossíntese , Cromatografia em Camada Delgada , Indústria Alimentícia , Sucos de Frutas e Vegetais , Concentração de Íons de Hidrogênio , Hidrólise , Microbiologia Industrial , Íons , Cinética , Malus , Metais/química , Peso Molecular , Filogenia , RNA Ribossômico 16S/metabolismo , Amido/metabolismo , Tensoativos/química , Temperatura
2.
Food Chem ; 339: 127896, 2021 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-32866696

RESUMO

Jackfruits are nutritionally rich fruit crop indigenous to the humid tropics, known by their place of origin. In the present study, using multielemental profiling of fruit samples, we demonstrated the discrimination of different jack fruit germplasm based on their geographical origin in India. The concentration of 24 elements in soil and fruit were determined by inductively coupled plasma mass spectrometry (ICP-MS). ANOVA revealed the significant difference of these 24 elements amongst the geographical locations both in soils and fruits. The correlation between soil and fruit ionome indicated the major influence of germplasm and other locational factors on the acquisition and accumulation of fruit multi elemental characteristics with minimal contribution of soil elements. Among the multivariate analysis tools, linear discriminant analysis (LDA) of fruit multi elemental fingerprint was found to be an efficient tool for discrimination of geographical origin of Indian jackfruits.


Assuntos
Artocarpus/química , Solo/química , Artocarpus/metabolismo , Análise Discriminante , Frutas/química , Frutas/metabolismo , Índia , Íons/análise , Espectrometria de Massas/métodos , Metais/química , Análise de Componente Principal
3.
Chemosphere ; 262: 127723, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32799138

RESUMO

Removing dissolved organic matter (DOM) with polyaluminium chloride is one of the primary goals of drinking water treatment. In this study, a new HMW framework was proposed, which divided the factors affecting coagulation into three parts consisting of hydraulic condition (H), metal salt (M), and background water matrix (W). In this framework, H, M and W were assumed to be interacted with each other and combined to determine coagulation efficiency. We investigated the feasibility of the framework to determine the treatment efficiency through mathematical models. Results showed that non-linear artificial neural network (ANN) model was a better fit to the experimental data than the linear partial least squares (PLS) model: the ANN model could explain 76% of the total variations while the PLS could only explain 71%. The PLS did not follow the variations of observed values adequately. These experiments showed that the interaction between the HMW framework components were not simple linear relationships. The ANN model was able to optimize the composition of the HMW framework improving the efficiency of DOM removal through the components of HMW such as velocity gradient (G value), coagulant dosage, solution pH, and background water matrix. Overall, HMW framework is a new classification of factors affecting coagulation, leading to a better understanding of the coagulation process and sensitivity to influencing variables.


Assuntos
Modelos Teóricos , Redes Neurais de Computação , Purificação da Água/métodos , Hidróxido de Alumínio/química , Água Potável , Concentração de Íons de Hidrogênio , Metais/química
4.
J Chromatogr A ; 1636: 461792, 2021 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-33340747

RESUMO

Chiral metal-organic cages (MOCs) are a new type of porous materials with unique molecular recognition ability, which have received research attention as a chiral stationary phase (CSP) for gas chromatography (GC). Herein, we report the detailed investigation of a chiral MOC ([Cu12(LPA)12(H2O)12], PA = L-phenylalanine, MOC-PA) as a novel stationary phase for GC separations. The MOC-PA capillary column exhibited a high-resolution performance for a wide range of analytes, including n-alkanes, n-alcohols, esters, aromatic compounds and the Grob mixture, positional isomers and racemates. In particular, MOC-PA coated column displayed good resolution and performance for amino acid derivatives. Moreover, the MOC-PA column showed excellent separation repeatability and reproducibility. The relative standard deviation (RSD) values for the retention times were in the range of 0.16-0.30% for run to run (n = 3), 0.31-0.77% for day-to-day (n = 3), and 3.6-4.7% for column-to-column (n = 3), respectively. The experimental results showed that MOC-PA had great potential as a GC stationary phase.


Assuntos
Cromatografia Gasosa/métodos , Metais/química , Compostos Orgânicos/química , Álcoois/química , Alcanos/química , Ésteres/química , Fenilalanina/química , Reprodutibilidade dos Testes , Espectroscopia de Infravermelho com Transformada de Fourier , Estereoisomerismo , Termogravimetria , Difração de Raios X
5.
Chemosphere ; 263: 127965, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32814135

RESUMO

Developing low-cost, high-efficiency catalysts for advanced oxidation processes remain a key issue for the degradation of organic pollutants. In this study, a novel FeCo2O4/rectorite composite was synthesized via a facile combustion process and employed to activate peroxymonosulfate (PMS) for dealing with atrazine (ATZ). The addition of rectorite could result in higher specific surface area, smaller pore size and more hydroxyl groups, which were beneficial to enrich pollutants to the adsorption sites and provide sufficient reactive sites. After meticulous evaluation, the degradation efficiency of FeCo2O4/rectorite composite towards ATZ exhibited improved PMS activation efficiency which was about 2.6 times than that of pure FeCo2O4. Based on the characterization results, the sulfate radicals and hydroxyl radicals were considered to be the main free radicals which were involved into the circulation of Co(II)-Co(III)-Co(II) as well as the oxidation of ≡Fe(II), which was responsible for the remarkable catalytic efficiency. In addition, the chemical stability and superior catalytic performance of FeCo2O4/rectorite should also be attributed to the chemical combination between metal ions and the surface hydroxyl groups of rectorite. Overall, these findings are beneficial for understanding the mechanism of PMS activation by natural mineral-based catalysts and contributing to the practical application of sulfate-based technology for organic wastewater treatment.


Assuntos
Metais/química , Peróxidos/química , Poluentes Químicos da Água/química , Silicatos de Alumínio , Atrazina/química , Catálise , Radical Hidroxila/química , Minerais , Modelos Químicos , Nanopartículas , Oxirredução , Papel (figurativo) , Sulfatos
6.
Food Chem ; 339: 127680, 2021 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-32860999

RESUMO

Coconut water (Cocos Nucifera) is shown to be a source of essential elements present in the form of low-molecular weight stable complexes known for their bio-availability. The total element concentrations were in the range of 0.2-2.7, 0.3-1, 3-14 and 0.5-2 ppm for Fe, Cu, Mn, and Zn, respectively, and varied as a function of the origin of the nut and its maturity. Speciation was investigated by size-exclusion chromatography - inductively coupled plasma mass spectrometry (ICPMS), and hydrophilic interaction liquid chromatography (HILIC) - electrospray-OrbitrapMS. The metal species identified included: iron complexes with citrate and malate: FeIII(Cit)3(Mal), FeIII(Cit)2(Mal)2, FeIII(Mal)2, glutamine: FeIII(Glu)2 and nicotianamine: FeII(NA); copper complexes with phenylanine: CuII(Phe)2 and CuII(Phe)3 and nicotianamine: CuII(NA); zinc complexes with citrate: ZnII(Cit)2 and nicotianamine ZnII(NA) and manganese complex with asparagine MnII(Asp)2. The contributions of the individual species to the total elements concentrations could be estimated by HILIC - ICP MS.


Assuntos
Cocos/química , Sucos de Frutas e Vegetais/análise , Metais/análise , Oligoelementos/análise , Oligoelementos/química , Ácido Azetidinocarboxílico/análogos & derivados , Ácido Azetidinocarboxílico/análise , Ácido Azetidinocarboxílico/química , Cromatografia em Gel , Cromatografia Líquida , Ácido Cítrico/análise , Ácido Cítrico/química , Análise de Alimentos/métodos , Malatos/análise , Malatos/química , Metais/química , Peso Molecular , Espectrometria de Massas por Ionização por Electrospray
7.
J Vis Exp ; (166)2020 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-33346192

RESUMO

Measuring the size distribution of the particles in a powder is a common activity in science and industry. Measuring the shape distribution of the particles is much less common. However, the shape and size of powder particles are not independent quantities. All known size/shape measurement techniques either assume a spherical shape or measure the shape in two dimensions only. The X-ray computed tomography (XCT) based method presented here measures both size and shape in 3D without making any assumptions. Starting from a 3D image of particles, the method can mathematically classify particles according to shape, for example particles composed of several smaller particles welded together as opposed to single particles that are not necessarily spherical. Of course, defining a single number as the "size" or "shape" of a random non-spherical particle is not possible in principle, leading to many ways to estimate particle size and shape via various interlinked parameters, which can all be generated from this complete 3D characterization in the form of averages and distributions. The necessary experimental procedures, mathematical analysis, and computer analysis are described and an example is given for a metal powder. The technique is limited to particles that can be imaged by XCT with a minimum of about 1000 voxels per particle volume.


Assuntos
Algoritmos , Imageamento Tridimensional , Metais/química , Tamanho da Partícula , Tomografia Computadorizada por Raios X , Porosidade , Pós
8.
Phys Med Biol ; 65(22): 225013, 2020 11 12.
Artigo em Inglês | MEDLINE | ID: mdl-33179612

RESUMO

In this study the metric of detective quantum efficiency (DQE) was applied to Cherenkov imaging systems for the first time, and results were compared for different detector hardware, gain levels and with imaging processing for noise suppression. Intensified complementary metal oxide semiconductor cameras using different image intensifier designs (Gen3 and Gen2+) were used to image Cherenkov emission from a tissue phantom in order to measure the modulation transfer function (MTF) and noise power spectrum (NPS) of the systems. These parameters were used to calculate the DQE for varying acquisition settings and image processing steps. MTF curves indicated that the Gen3 system had superior contrast transfer and spatial resolution than the Gen2+ system, with [Formula: see text] values of 0.52 mm-1 and 0.31 mm-1, respectively. With median filtering for noise suppression, these values decreased to 0.50 mm-1 and 0.26 mm-1. The maximum NPS values for the Gen3 and Gen2+ systems at high gain were 1.3 × 106 mm2 and 9.1 × 104 mm2 respectively, representing a 14x decrease in noise power for the Gen2+ system. Both systems exhibited increased NPS intensity with increasing gain, while median filtering lowered the NPS. The DQE of each system increased with increasing gain, and at the maximum gain levels the Gen3 system had a low-frequency DQE of 0.31%, while the Gen2+ system had a value of 1.44%. However, at a higher frequency of 0.4 mm-1, these values became 0.54% and 0.03%. Filtering improved DQE for the Gen3 system and reduced DQE for the Gen2+ system and had a mix of detrimental and beneficial qualitative effects by decreasing the spatial resolution and sharpness but also substantially lowering noise. This methodology for DQE measurement allowed for quantitative comparison between Cherenkov imaging cameras and improvements to their sensitivity, and yielded the first formal assessment of Cherenkov image formation efficiency.


Assuntos
Processamento de Imagem Assistida por Computador/métodos , Metais/química , Óxidos/química , Teoria Quântica , Radioterapia Guiada por Imagem , Semicondutores , Imagens de Fantasmas
9.
Nat Commun ; 11(1): 5554, 2020 11 03.
Artigo em Inglês | MEDLINE | ID: mdl-33144560

RESUMO

Phase separation of specific biomolecules into liquid droplet-like condensates is a key mechanism to form membrane-less organelles, which spatio-temporally organize diverse biochemical processes in cells. To investigate the working principles of these biomolecular condensates as dynamic reaction centers, precise control of diverse condensate properties is essential. Here, we design a strategy for metal ion-induced clustering of minimal protein modules to produce liquid protein condensates, the properties of which can be widely varied by simple manipulation of the protein clustering systems. The droplet forming-minimal module contains only a single receptor protein and a binding ligand peptide with a hexahistidine tag for divalent metal ion-mediated clustering. A wide range of protein condensate properties such as droplet forming tendency, droplet morphology, inside protein diffusivity, protein recruitment, and droplet density can be varied by adjusting the nature of receptor/ligand pairs or used metal ions, metal/protein ratios, incubation time, binding motif variation on recruited proteins, and even spacing between receptor/ligand pairs and the hexahistidine tag. We also demonstrate metal-ion-induced protein phase separation in cells. The present phase separation strategy provides highly versatile protein condensates, which will greatly facilitate investigation of molecular and structural codes of droplet-forming proteins and the monitoring of biomolecular behaviors inside diverse protein condensates.


Assuntos
Proteínas de Membrana/química , Metais/química , Motivos de Aminoácidos , Sequência de Aminoácidos , Análise por Conglomerados , Fluorescência , Células HeLa , Humanos , Íons , Ligantes , Mutação/genética , Engenharia de Proteínas , Domínios de Homologia de src
10.
J Chromatogr A ; 1633: 461649, 2020 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-33166743

RESUMO

Different degrees of protein purity have been observed in immobilized metal affinity chromatography ranging from extremely high purity to moderate and low purity. It has been hypothesized that the host cell protein composition and the metal ligands are factors governing the purity of a protein obtained after immobilized metal affinity chromatography (IMAC). Ni nitrilotriacetic acid (NTA) has become the first choice for facile His-tagged protein purification, but alternative ligands such as iminodiacetic acid (IDA) with other immobilized metal ions such as Zn, Cu and Co are valuable options when the expected purity or binding capacity is not reached. Especially Cu and Zn are very attractive, due to their reduced environmental and safety concerns compared to Ni. Co and Zn are more selective than Ni and Cu. This increased selectivity comes at the cost of weaker binding. In this work, the influence of ligand choice on protein purity after IMAC was evaluated by several methods, including peptide mapping. His-tagged GFP was used as model protein. We found that host cell protein (HCP) content varies drastically between ligands, as IDA eluates generally showing higher HCP concentrations than NTA. The relative content of the key amino acids His, Cys and Trp in the sequence of the co-eluted protein does not suffice to explain co-eluting propensity. The co-elution of HCPs is mostly influenced by metal binding clusters on the protein surface and not by total content or surface concentration of metal interacting amino acids. Prediction of co-elution is not dependent on these clusters alone, due to protein-protein interactions, indicted by a relative low metal binding cluster score but high co-elution propensity and in a lot of cases these proteins are often part of complex such as ribosome and chaperones. The different co-eluting proteins were presented by a heatmap with a dendrogram. Ward's linkage method was used to calculate the distance between groups of co-eluting proteins. Clustering of co-eluting HCPs was observed according to ligand and by metal ions, with Zn and Co forming one cluster and Ni and Cu another. The co-elution of host cell proteins can be explained by clusters of metal interacting amino acids on the protein surface and by protein-protein interactions. While Ni NTA still appears to be highly advantageous, it might not be the cure-all for all applications.


Assuntos
Cromatografia de Afinidade , Íons/química , Ligantes , Metais/química , Proteômica/métodos , Iminoácidos/química , Ácido Nitrilotriacético/química
11.
Phys Chem Chem Phys ; 22(45): 26502-26508, 2020 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-33185211

RESUMO

A comprehensive photophysical study of a series of purines, doubly decorated at C2 and C6 positions with identical fragments ranging from electron acceptor to donor groups of different strengths, is presented. The asymmetry of substitutions creates a unique molecular D-A-D' structure possessing two independent electronic charge transfer (CT) systems attributed to each fragment and exhibiting dual-band fluorescence. Moreover, the inherent property of coordination of metal ions by purines was enriched due to a presence of nearby triazoles used as spacers for donor or acceptor fragments. New molecules present a bidentate coordination mode, which makes the assembly of several ligands with one metal cation possible. This property was exploited to create a new concept of a ratiometric chemical fluorescence sensor involving the photoinduced electron transfer between branches of different ligands as a mechanism of fluorescence modulation.


Assuntos
Transporte de Elétrons , Ligantes , Transporte de Elétrons/fisiologia , Fluorescência , Íons/química , Metais/química , Purinas/química , Eletricidade Estática , Triazinas/química
12.
Sci Rep ; 10(1): 16896, 2020 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-33037243

RESUMO

Oil exploration's devastation on health and the environment may far outweigh its economic benefits. An oil spill occurred at Egbokodo River in Delta State, Nigeria, thereby polluting the land and water bodies. The study was therefore aimed at evaluating the impacts of iron, lead, cadmium, and chromium on the zooplankton community structure of Egbokodo River and the potential health risks. Zooplankton and surface water samples were collected to investigate the concentrations of trace metals and zooplankton abundance. The associated carcinogenic and non-carcinogenic effects of the metals in the water were analyzed. Trace metal concentrations in the surface water were determined using atomic absorption spectroscopy (Philips model PU 9100) and zooplankton samples were collected using a hydrobios plankton net (mesh size 25 µm). Total petroleum hydrocarbons (TPH) and oil and grease (OG) were determined using Agilent 7890B gas chromatography coupled to flame ionization detector (GC-FID) and volumetric analysis respectively. The trend of the abundance of zooplanktons cross the river was 18 individuals (Station A) < 100 individuals (Station B) < 155 individuals (Station C). Cyclopoida proved to be the most resilient to the impacts of the oil spill. On a taxa basis, the order of abundance among Calanoida, Cyclopoida, Cladoceran, and Harpacticoida was Station C > Station B > Station A, except in Amphipoda where Station B > Station C > Station A was observed. Iron and lead posed significant carcinogenic risks that are liable to be inflicted by the ingestion of the water. The cumulative non-carcinogenic health risk in the male was the only significant (> 1) among the age groups. Total petroleum hydrocarbons (TPH), oil and grease (OG), iron, and lead had notable impacts on the general abundance of zooplankton in the aquatic habitat. The dominance of the Cyclopoida in the river buttressed the impact of the oil spill which warrants a prompt remediation measure. The pollution had notable ecological impacts on the zooplankton community structure of the aquatic habitat. The adults in the nearby human populations are liable to elicit carcinogenic health challenges associated with lead and iron ingestion. The males are at risk of non-carcinogenic illnesses which are associated with the combined toxicity effects of all the metals. The study suggests that the pollution in Egbokodo River was validated by the dominance of the Cyclopoida in the aquatic habitat. The study confers bioindicator reputation on the Cyclopoida for future biomonitoring studies.


Assuntos
Cádmio/química , Cromo/química , Ferro/química , Chumbo/química , Rios/química , Zooplâncton/efeitos dos fármacos , Animais , Cádmio/efeitos adversos , Cromo/efeitos adversos , Ecossistema , Monitoramento Ambiental/métodos , Poluição Ambiental/efeitos adversos , Humanos , Hidrocarbonetos/efeitos adversos , Hidrocarbonetos/química , Ferro/efeitos adversos , Chumbo/efeitos adversos , Masculino , Metais/efeitos adversos , Metais/química , Nigéria , Petróleo/efeitos adversos , Poluição por Petróleo/efeitos adversos , Floresta Úmida , Poluentes Químicos da Água/efeitos adversos , Poluentes Químicos da Água/química
13.
Sci Rep ; 10(1): 16293, 2020 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-33004902

RESUMO

α-Synuclein is an intrinsically disordered protein that can self-aggregate and plays a major role in Parkinson's disease (PD). Elevated levels of certain metal ions are found in protein aggregates in neurons of people suffering from PD, and environmental exposure has also been linked with neurodegeneration. Importantly, cellular interactions with metal ions, particularly Ca2+, have recently been reported as key for α-synuclein's physiological function at the pre-synapse. Here we study effects of metal ion interaction with α-synuclein at the molecular level, observing changes in the conformational behaviour of monomers, with a possible link to aggregation pathways and toxicity. Using native nano-electrospray ionisation ion mobility-mass spectrometry (nESI-IM-MS), we characterize the heterogeneous interactions of alkali, alkaline earth, transition and other metal ions and their global structural effects on α-synuclein. Different binding stoichiometries found upon titration with metal ions correlate with their specific binding affinity and capacity. Subtle conformational effects seen for singly charged metals differ profoundly from binding of multiply charged ions, often leading to overall compaction of the protein depending on the preferred binding sites. This study illustrates specific effects of metal coordination, and the associated electrostatic charge patterns, on the complex structural space of the intrinsically disordered protein α-synuclein.


Assuntos
alfa-Sinucleína/química , Cálcio/química , Cobre/química , Proteínas Intrinsicamente Desordenadas/química , Espectrometria de Mobilidade Iônica , Espectrometria de Massas , Metais/química , Potássio/química , Conformação Proteica , Sódio/química , Zinco/química
14.
J Cancer Res Ther ; 16(5): 1119-1124, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33004757

RESUMO

Objective: We sought to analyze the efficacy and safety of preserving the Oddis sphincter during metallic biliary stent implantation in patients with malignant obstructive jaundice. Materials and Methods: In a retrospective analysis, 133 patients with malignant obstructive jaundice who were admitted to our hospital from January 2010 to January 2017 and who underwent metallic biliary stent implantation were divided into two groups - the Oddis sphincter retention group (n = 55) and the Oddis sphincter nonretention group (n = 78) - according to whether the Oddis sphincter was left untouched during stent placement. The patient clinical data as well as information on complications, time of stent patency, improvement in liver function, and decline of serum bilirubin were reviewed and evaluated. Statistical analysis was performed using the Statistical Package for the Social Sciences version 19.0 (IBM Corp., Armonk, NY, USA, USA) and Prism version 7 (GraphPad Software, San Diego, CA, USA). Results: The median follow-up time was 9.6 months (range: 1-20 months) and there was no significant difference in general clinical information between the two groups. However, the incidence rates of acute biliary infection, recurrent biliary infection, acute pancreatitis, chronic pancreatitis, and asymptomatic pancreatic enzyme levels were higher in the Oddis sphincter retention group and the differences were all statistically significant (P < 0.05). Conversely, there were no significant differences in bilirubin decline, liver function improvement, and stent patency between the two groups (P > 0.05). Conclusion: Leaving the Oddis sphincter untouched during biliary stent placement can reduce the incidence of postoperative complications, while there was no effect on stent patency or jaundice relief. Therefore, it is recommended to preserve the Oddis sphincter when the stenosis is more than 3 cm above the duodenal papilla.


Assuntos
Neoplasias dos Ductos Biliares/cirurgia , Icterícia Obstrutiva/cirurgia , Testes de Função Hepática/métodos , Metais/química , Próteses e Implantes , Esfíncter da Ampola Hepatopancreática/cirurgia , Stents/estatística & dados numéricos , Adulto , Idoso , Neoplasias dos Ductos Biliares/patologia , Feminino , Humanos , Icterícia Obstrutiva/patologia , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Esfíncter da Ampola Hepatopancreática/patologia , Resultado do Tratamento
15.
J Oleo Sci ; 69(11): 1427-1436, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-33055444

RESUMO

This paper presents the results of a kinetic study performed between ninhydrin and a Ni(II) dipeptide complex under various conditions. The rate of formation of the imine adduct was measured spectrophotometrically both in plain aqueous media and in aqueous micellar media in which CTAB (cetyltrimethylammonium bromide) is used as the surfactant. These studies were carried out at pH 5 and over a temperature a range of 50 to 70°C. Studies were also conducted to elucidate the effect of some organic sodium salts on the rate of this reaction. In these studies, it was found that the formation of imine adduct followed a first-order kinetics with respect to [Ni(II)-Gly-Leu]+ in both aqueous and micellar medium. A fractional-order kinetics was observed with respect to ninhydrin, again in both aqueous and micellar media. Increase in the total concentration of CTAB from 0 to 40×10-3 mol dm-3 resulted in approximately two folds increase in the pseudo-first-order rate constant (kψ). The rate constant (kΨ) in micellar medium first increased with increase in CTAB concentration, reached a maximum value, and finally, with further increase in CTAB concentration, a decreasing effect was observed. Quantitative kinetic analysis of kψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. The rate profile in presence of CTAB suggests a cooperative effect in the enhanced formation of the imine adduct as is commonly found in enzyme catalyzed reactions. Addition of organic sodium salts (such as benzoate, salicylate and tosylate) enhanced the rate at lower concentrations but rates start to decrease at higher concentrations. This suggests that tightly binding organic counter-anions were the most effective. Viscosity of the reaction media seems to affect the kinetic behavior in micellar media.


Assuntos
Cetrimônio/química , Dipeptídeos/química , Iminas/química , Metais/química , Ninidrina/química , Tensoativos/química , Ânions/química , Benzoatos/química , Catálise , Concentração de Íons de Hidrogênio , Micelas , Fenômenos de Química Orgânica , Salicilatos/química , Espectrofotometria , Temperatura , Viscosidade , Água/química
16.
Nat Commun ; 11(1): 5241, 2020 10 16.
Artigo em Inglês | MEDLINE | ID: mdl-33067443

RESUMO

To understand how the RuvC catalytic domain of Class 2 Cas proteins cleaves DNA, it will be necessary to elucidate the structures of RuvC-containing Cas complexes in their catalytically competent states. Cas12i2 is a Class 2 type V-I CRISPR-Cas endonuclease that cleaves target dsDNA by an unknown mechanism. Here, we report structures of Cas12i2-crRNA-DNA complexes and a Cas12i2-crRNA complex. We reveal the mechanism of DNA recognition and cleavage by Cas12i2, and activation of the RuvC catalytic pocket induced by a conformational change of the Helical-II domain. The seed region (nucleotides 1-8) is dispensable for RuvC activation, but the duplex of the central spacer (nucleotides 9-15) is required. We captured the catalytic state of Cas12i2, with both metal ions and the ssDNA substrate bound in the RuvC catalytic pocket. Together, our studies provide significant insights into the DNA cleavage mechanism by RuvC-containing Cas proteins.


Assuntos
DNA de Cadeia Simples/metabolismo , Desoxirribonuclease I/química , Desoxirribonuclease I/metabolismo , Metais/metabolismo , Catálise , Domínio Catalítico , Clivagem do DNA , DNA de Cadeia Simples/química , DNA de Cadeia Simples/genética , Desoxirribonuclease I/genética , Íons/química , Íons/metabolismo , Metais/química
17.
Phys Chem Chem Phys ; 22(43): 25042-25053, 2020 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-33112337

RESUMO

The "specific" interaction between metal cations (Na+, Ca2+, Mg2+, and Zn2+) and the charged COO- group, and the "non-specific" interaction between these cations and the peptide backbone of a zwitterionic trialanine (Ala3) in aqueous solutions were examined in detail, using linear infrared (IR) absorptions of the COO- symmetric stretching and the amide-II (mainly the C-N stretching) modes as IR probes. Different IR spectral changes in peak positions and intensities of the two IR probes clearly demonstrate their sensitivities to nearby cation distributions in distance and population. Quantum chemistry calculations and molecular dynamics simulations were used to describe the cation-peptide interaction picture. These combined results suggest that Na+ and Ca2+ tend to bind to the COO- group in the bidentate form, while Mg2+ and Zn2+ tend to bind to the COO- group in the pseudo-bridging form. The results also show that while all three divalent cations indirectly interact with the peptide backbone with large population, Ca2+ and Mg2+ can be sometimes distributed very close to the backbone. Such a non-specific cation interaction can be moderately sensed by the C-N stretching of the amide-II mode when cations approach the polar amide C[double bond, length as m-dash]O group, and is also influenced by the NH3+ charge group located at the N-terminus. The results suggest that the experimentally observed complication of the Hofmeister cation series shall be understood as a combined specific and non-specific cation-peptide interactions.


Assuntos
Alanina/química , Amidas/química , Cátions/química , Metais/química , Solução Salina/química , Vibração
18.
Phys Med Biol ; 65(19): 195002, 2020 09 25.
Artigo em Inglês | MEDLINE | ID: mdl-32976116

RESUMO

The susceptibility of MRI to metallic objects leads to void MR signal and missing information around metallic implants. In addition, body truncation occurs in MR imaging for large patients who exceed the transaxial field-of-view of the scanner. Body truncation and metal artefacts translate to incomplete MRI-derived attenuation correction (AC) maps, consequently resulting in large quantification errors in PET imaging. In this work, we propose a deep learning-based approach to predict the missing information/regions in MR images affected by metallic artefacts and/or body truncation aiming at reducing quantification errors in PET/MRI. Twenty-five whole-body (WB) co-registered PET, CT, and MR images were used for training and evaluation of the object completion approach. CT-based attenuation corrected PET images were considered as reference for the quantitative evaluation of the proposed approach. Its performance was compared to the 3-class segmentation-based AC approach (containing background air, soft-tissue and lung) obtained from MR images. The metal-induced artefacts affected 8.1 ± 1.8% of the volume of the head region when using the 3-class AC maps. This error reduced to 0.9 ± 0.5% after application of object completion on MR images. Consequently, quantification errors in PET images reduced from -57.5 ± 11% to -18.5 ± 5% in the head region after metal artefact correction. The percentage of the torso volume affected by body truncation in the 3-class AC maps reduced from 9.8 ± 1.9% to 0.6 ± 0.3% after truncation compensation. PET quantification errors in the affected regions were also reduced from -45.5 ± 10% to -9.5 ± 3% after truncation compensation. The quantitative results demonstrated promising performance of the proposed approach towards the completion of MR images corrupted by metal artefacts and/or body truncation in the context of WB PET/MR imaging.


Assuntos
Aprendizado Profundo , Implantes Dentários/normas , Processamento de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética/métodos , Metais/química , Imagem Multimodal/métodos , Tomografia por Emissão de Pósitrons/métodos , Algoritmos , Artefatos , Humanos , Tomografia Computadorizada por Raios X/métodos
19.
Nat Commun ; 11(1): 4557, 2020 09 11.
Artigo em Inglês | MEDLINE | ID: mdl-32917908

RESUMO

Why metalloenzymes often show dramatic changes in their catalytic activity when subjected to chemically similar but non-native metal substitutions is a long-standing puzzle. Here, we report on the catalytic roles of metal ions in a model metalloenzyme system, human carbonic anhydrase II (CA II). Through a comparative study on the intermediate states of the zinc-bound native CA II and non-native metal-substituted CA IIs, we demonstrate that the characteristic metal ion coordination geometries (tetrahedral for Zn2+, tetrahedral to octahedral conversion for Co2+, octahedral for Ni2+, and trigonal bipyramidal for Cu2+) directly modulate the catalytic efficacy. In addition, we reveal that the metal ions have a long-range (~10 Å) electrostatic effect on restructuring water network in the active site. Our study provides evidence that the metal ions in metalloenzymes have a crucial impact on the catalytic mechanism beyond their primary chemical properties.


Assuntos
Anidrases Carbônicas/química , Íons/química , Metaloproteínas/química , Metais/química , Sítios de Ligação , Anidrase Carbônica II/química , Anidrase Carbônica II/metabolismo , Anidrases Carbônicas/metabolismo , Catálise , Domínio Catalítico , Cobalto/química , Cobre/química , Cristalografia por Raios X , Humanos , Íons/metabolismo , Cinética , Metaloproteínas/metabolismo , Metais/metabolismo , Modelos Moleculares , Níquel/química , Conformação Proteica , Relação Estrutura-Atividade , Especificidade por Substrato , Zinco/química
20.
Inorg Chem ; 59(16): 11542-11553, 2020 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-32799475

RESUMO

The superfamily of heme copper oxidases reduces molecular oxygen or nitric oxide, and the active sites comprise a high-spin heme group (a3 or b3) and a non-heme metal (CuB or FeB). The cbb3 C family of cytochrome c oxidases, with the high-spin heme b3 and CuB in the active site, is a subfamily of the heme copper oxidases that can reduce both molecular oxygen, which is the main substrate, and nitric oxide. The mechanism for NO reduction in cbb3 oxidase is studied here using hybrid density functional theory and compared to other cytochrome c oxidases (A and B families), with a high-spin heme a3 and CuB in the active site, and to cytochrome c dependent NO reductase, with a high-spin heme b3 and a non-heme FeB in the active site. It is found that the reaction mechanism and the detailed reaction energetics of the cbb3 oxidases are not similar to those of cytochrome c dependent NO reductase, which has the same type of high-spin heme group but a different non-heme metal. This is in contrast to earlier expectations. Instead, the NO reduction mechanism in cbb3 oxidases is very similar to that in the other cytochrome c oxidases, with the same non-heme metal, CuB, and is independent of the type of high-spin heme group. The conclusion is that the type of non-heme metal (CuB or FeB) in the active site of the heme copper oxidases is more important for the reaction mechanisms than the type of high-spin heme, at least for the NO reduction reaction. The reason is that the proton-coupled reduction potentials of the active site cofactors determine the energetics for the NO reduction reaction, and they depend to a larger extent on the non-heme metal. Observed differences in NO reduction reactivity among the various cytochrome c oxidases may be explained by differences outside the BNC, affecting the rate of proton transfer, rather than in the BNC itself.


Assuntos
Heme/química , Metais/química , Óxido Nítrico/química , Oxirredutases/química , Domínio Catalítico , Oxirredução
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