Superabsorbent hydrogel composite made of cellulose nanofibrils and chitosan-graft-poly(acrylic acid)

Superabsorbent hydrogel composites based on cellulose nanofibrils and chitosan-graft-poly(acrylic acid) copolymer were developed in this work. The FTIR data showed that the copolymerization and the composite formation reaction were successfully performed. In addition, the XRD pattern indicated that the nanofibrils crystallinity was as high as 90%. A 2⁴⁻¹ fractional factorial design was employed to evaluate the effect of acrylic acid/chitosan molar ratio, crosslinker, initiator, and filler in the swelling capacity of hydrogel composites. By the analysis of variance (ANOVA), including F-test and P-values, it was found that the crosslinker and filler correspond to 40% and 30% of the evaluated response, respectively. The addition of nanofibrils provided faster equilibrium conditions as well as improved the swelling capacity in ca. 100 units, from 381 to 486. SEM images showed that the addition of nanofibrils into the hydrogel matrix increased the averaged-dimension of porous. Finally, the composites showed responsive behavior in relation to pH and salt solution. Such characteristics make these smart materials suitable for several technological applications.     

Hypercytolipidemia-induced cellular lipoapoptosis: cytostructural and endometabolic basis of progressive organo-involution following expression of diabetes (db/db) and obese (ob/ob) mutation syndromes

Onset expression of Type 2 (NIDDM) diabetes and obesity metabolic syndromes (DOS) are characterized by premature, progressive cytoatrophy and organo-involution induced by dysregulated cellular gluco- and lipo-metabolic cascades. The consequential systemic, interstitial and intracellular hyperlipidemia disrupts normal cytointegrity and metabolic responsivity to the established hypercaloric pericellular environments. The sequential cytostructural, metabolic and endocrine disturbances associated with the development of progressive DOS-associated hypercytolipidemia compromises cellular metabolic response cascades and promotes cytochemical disturbances which culminate with nuclear lipoapoptosis and cytoatrophy. The dramatic alterations in interstitial glucose and lipid (free fatty acids/triglycerides) concentrations are recognized to influence interstitial and cytoplasmic microchemical environments, which markedly alter cellular nutrient diffusion and active trans-membrane flux rates. The progressive exacerbation of interstitial and cytoplasmic lipid imbibition has been demonstrated to be associated with DNA fragmentation by lipo-infiltration into the chromatin matrix, inducing structural disruption and physical dissolution, indexed as nuclear lipoapoptosis. Therapeutic reduction of the severity of hypercytolipidemia-induced structural and cytochemical compromise promotes the restoration of homeostatic metabolic support for normalized cytostructural indices and supportive cellular gluco- and lipo-metabolic cascades. The re-establishment of a homeostatic interstitial microenvironment moderates the severity of cytolipidemic compromise within affected cell types, reduces nuclear lipo-infiltration and DNA lipo-dissolution, resulting in the preservation of cytostructural integrity. Through the therapeutic restoration of extra- and intra-cellular microchemical environments in genetically dysregulated metabolic syndrome models, the coincident cytochemical, endocrine and metabolic disturbances associated with progressive hypercytolipidemia, resulting from the expressed systemic hypercaloric environmental and hepato-pancreatic endometabolic disturbances which characterize Type 2 (NIDDM) diabetes–obesity and metabolic (X) syndromes, may be ameliorated.     

来源于糖丝菌双(2-羟乙基)对苯二甲酸酯水解酶的酶学性质表征及降解特性分析

聚对苯二甲酸乙二醇酯[poly(ethylene terephthalate),PET]降解酶的发掘是国内外研究的热点。双(2-羟乙基)对苯二甲酸酯[bis-(2-hydroxyethyl)terephthalic acid,BHET]是PET降解过程的一种中间化合物,会与PET竞争酶的底物结合位点,从而抑制PET进一步降解。因此,探寻新型BHET降解酶,对进一步提高PET的降解效率具有促进作用。本研究通过基因挖掘发现了一种来源于浅黄糖丝菌(Saccharothrix luteola)参与PET降解过程的水解酶基因sle(ID:CP064192.1,5085270–5086049),其编码的蛋白质可以将BHET水解为单(2-羟乙基)对苯二甲酸酯[mono-(2-hydroxyethyl)terephthalate,MHET]和对苯二甲酸(terephthalic acid,TPA)。将BHET水解酶(Sle)通过重组质粒在大肠杆菌(Escherichia coli)中异源表达,结果表明,在异丙基-β-D-硫代半乳糖苷(isopropyl-β-D-thiogalactoside,IPTG)诱导终浓度为0.4 mmol/L,诱导时长为12 h,诱导温度为20℃时蛋白的表达量最高。通过镍亲和层析、阴离子交换层析和凝胶过滤层析3步分离纯化,获得了高纯度的Sle重组蛋白;同时对其酶学性质进行了表征,Sle最适温度和pH分别为35℃和8.0,在25–35℃和pH 7.0–9.0区间内能保持80%以上的残余酶活,且金属离子Co^(2+)能提高酶活力;进一步通过同源序列及Sle复合物结构分析得知,该酶属于二烯酸内酯水解酶(dienelactone hydrolase,DLH)家族,具备该家族典型的催化三联体,预测其催化位点分别为S129、D175和H207,并初步分析了其催化机理。最后,利用高效液相色谱法(high performance liquid chromatography,HPLC)鉴定了该酶能够特异性降解BHET生成MHET和TPA,属于BHET降解酶。本研究为生物酶法高效降解PET塑料提供了新的酶资源。     

Quality by design (QbD) of amide isosteres: 5,5-Disubstituted isoxazolines as potent CRTh2 antagonists with favorable pharmacokinetic and drug-like properties

Isoxazoles are frequently used amide isosteres, as shown in the context of discovery of CRTh₂ antagonists from amide 1 to isoxazole 2. However, persistent agonism and poor solubility in isoxazole series presented challenges to its further development. Based on the concept of quality by design (QbD), 5,5-disubstituted isoxazolines 3 were introduced. The chirality at 5 position of isoxazolines controlled the switch between two modes of actions, which led to a novel series of pure antagonists. This non-planar motif also conferred a change of shape of these molecules, which avoided flat structures and improved their physical properties.     

Modeled responses of terrestrial ecosystems to elevated atmospheric CO2: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP)

Although there is a great deal of information concerning responses to increases in atmospheric CO₂ at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO₂ is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO₂. In this study, we analyze the responses of net primary production (NPP) to doubled CO₂ from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO₂ causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO₂ and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO₂ for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO₂ for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO₂ is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO₂ is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO₂ is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO₂. Received: 13 December 1996 / Accepted: 20 November 1997     

2,4-Dichlorophenoxyacetic Acid (2,4-D) Utilization by Delftia acidovorans MC1 at Alkaline pH and in the Presence of Dichlorprop is Improved by Introduction of the tfdK Gene

Growth of Delftia acidovorans MC1 on 2,4-dichlorophenoxyacetic acid (2,4-D) and on racemic 2-(2,4-dichlorophenoxy)propanoic acid ((RS)-2,4-DP) was studied in the perspective of an extension of the strain’s degradation capacity at alkaline pH. At pH 6.8 the strain grew on 2,4-D at a maximum rate (μ_max) of 0.158 h⁻¹. The half-maximum rate-associated substrate concentration (K_s) was 45 μM. At pH 8.5 μ_max was only 0.05 h⁻¹ and the substrate affinity was mucher lower than at pH 6.8. The initial attack of 2,4-D was not the limiting step at pH 8.5 as was seen from high dioxygenase activity in cells grown at this pH. High stationary 2,4-D concentrations and the fact that μ_max with dichlorprop was around 0.2 h⁻¹ at both pHs rather pointed at limited 2,4-D uptake at pH 8.5. Introduction of tfdK from D. acidovorans P4a by conjugation, coding for a 2,4-D-specific transporter resulted in improved growth on 2,4-D at pH 8.5 with μ_max of 0.147 h⁻¹ and K_s of 267 μM. Experiments with labeled substrates showed significantly enhanced 2,4-D uptake by the transconjugant TK62. This is taken as an indication of expression of the tfdK gene and proper function of the transporter. The uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP) reduced the influx of 2,4-D. At a concentration of 195 μM 2,4-D, the effect amounted to 90% and 50%, respectively, with TK62 and MC1. Cloning of tfdK also improved the utilization of 2,4-D in the presence of (RS)−2,4-DP. Simultaneous and almost complete degradation of both compounds occurred in TK62 up to D = 0.23 h⁻¹ at pH 6.8 and up to D = 0.2 h⁻¹ at pH 8.5. In contrast, MC1 left 2,4-D largely unutilized even at low dilution rates when growing on herbicide mixtures at pH 8.5.     

15-Deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) mediates repression of TNF-alpha by decreasing levels of acetylated histone H3 and H4 at its promoter

Thirty-nine missense mutations, which had been identified in rod monochromacy or related disorders, in the CNGA3 subunit of cone photoreceptor cGMP-gated channels were analyzed. HEK293 cells were transfected with cDNA of the human CNGA3 subunit harboring each of these mutations in an expression vector. Patch-clamp recordings demonstrated that 32 of the 39 mutants did not show cGMP-activated current, suggesting that these 32 mutations cause a loss of function of the channels. From the remaining 7 mutants that showed cGMP-activated current, two mutations in the cyclic nucleotide-binding domain, T565M or E593K, were further studied. The half-maximal activating concentration (K(1/2)) for cGMP in the homomeric CNGA3-T565M channels (160microM) was 17.8-fold higher than that of the homomeric wild-type CNGA3 channels (9.0microM). Conversely, the K(1/2) for cGMP in the homomeric CNGA3-E593K channels (3.0microM) was 3-fold lower than that of the homomeric wild-type CNGA3 channels. These results suggest that the T565M and E593K mutations alter the apparent affinity for cGMP of the channels to cause cone dysfunction, resulting in rod monochromacy.     

Identification and catalytic characterization of a nonribosomal peptide synthetase-like (NRPS-like) enzyme involved in the biosynthesis of echosides from Streptomyces sp. LZ35

Echosides, isolated from Streptomyces sp. LZ35, represent a class of para-terphenyl natural products that display DNA topoisomerase I and IIα inhibitory activities. By analyzing the genome draft of strain LZ35, the ech gene cluster was identified to be responsible for the biosynthesis of echosides, which was further confirmed by gene disruption and HPLC analysis. Meanwhile, the biosynthetic pathway for echosides was proposed. Furthermore, the echA-gene, encoding a tri-domain nonribosomal peptide synthetase (NRPS)-like enzyme, was identified as a polyporic acid synthetase and biochemically characterized in vitro. This is the first study to our knowledge on the biochemical characterization of an Actinobacteria quinone synthetase, which accepts phenylpyruvic acid as a native substrate. Therefore, our results may help investigate the function of other NRPS-like enzymes in Actinobacteria.     

In intact leaves, the maximum fluorescence level (FM) is independent of the redox state of the plastoquinone pool: A DCMU-inhibition study

The effects of DCMU (3-(3′,4′-dichlorophenyl)-1,1-dimethylurea) on the fluorescence induction transient (OJIP) in higher plants were re-investigated. We found that the initial (F₀) and maximum (F_M) fluorescence levels of DCMU-treated leaves do not change relative to controls when the treatment is done in complete darkness and DCMU is allowed to diffuse slowly into the leaves either by submersion or by application via the stem. Simultaneous 820 nm transmission measurements (a measure of electron flow through Photosystem I) showed that in the DCMU-treated samples, the plastoquinone pool remained oxidized during the light pulses whereas in uninhibited leaves, the F_M level coincided with a fully reduced electron transport chain. The identical F_M values with and without DCMU indicate that in intact leaves, the F_M value is independent of the redox state of the plastoquinone pool. We also show that (i) the generally observed F₀ increase is probably due to the presence of (even very weak) light during the DCMU treatment, (ii) vacuum infiltration of leaf discs leads to a drastic decrease of the fluorescence yield, and in DCMU-treated samples, the F_M decreases to the I-level of their control (leaves vacuum infiltrated with 1% ethanol), (iii) and in thylakoid membranes, the addition of DCMU lowers the F_M relative to that of a control sample.