Importance of an extreme C-terminal motif of a family I.3 lipase for stability

A five-residue sequence motif (VTLVG) located at positions 15-19 from the C-terminus of family I.3 lipase from Pseudomonas sp. MIS38 (PML) and an extreme C-terminal motif (DGIVIA) located at the C-terminus of PML are relatively well conserved in the passenger proteins of type 1 secretion system (T1SS). To analyze the role of these motifs, four mutant proteins of PML (PMLΔ5, PMLΔ10, 3A-PML and 2A-PML) were constructed. PMLΔ5 and PMLΔ10 lack the C-terminal 5 and 10 residues of PML, respectively. 3A-PML has triple mutations within an extreme C-terminal motif and 2A-PML has double mutations within a five-residue sequence motif. Secretion of these proteins was analyzed using Escherichia coli DH5 cells carrying Lip system (T1SS for family I.3 lipase). The secretion level of 2A-PML was dramatically reduced when compared with that of PML, whereas the secretion level of 3A-PML was comparable to that of PML, indicating that a five-residue sequence motif, instead of an extreme C-terminal motif, is required for secretion of PML. None of the mutations and truncations seriously affects the enzymatic activity of PML. However, 3A-PML, PMLΔ5 and PMLΔ10 were less stable than PML by 2.1, 7.6 and 7.6°C in T(1/2), respectively, and by 5.0, 21.3 and 17.9 kJ/mol in ΔG(H(2)O), respectively. These results indicate that an extreme C-terminal motif of PML is important for stability.     

Stability effects associated with the introduction of a partial and a complete Ca2+-binding site into human lysozyme

Two mutants of human lysozyme were synthesized. Mutant A92D,in which Ala92 was substituted by Asp, contains a partial Ca²⁺-bindingsite and mutant M4, in which Ala83, Gm86, Asn88 and Ala92 werereplaced by Lys, Asp, Asp and Asp respectively, contains thecomplete Ca -binding site of bovine a-lactalbumin. The Ca²⁺-bindingconstants of wild type human lysozyme and of mutants A92D andM4, measured at 25C and pH 7.5, were 2(1) x 102 M"1, 8(2)x l^M"1 and 9(0.5) x 10* M"1 respectively. Information gatheredfrom mkrocalorimetrk and CD spectro-scopic measurements indicatesthat the conformational changes of the M4 mutant lysozyme, inducedby Ca²⁺ binding, are smaller than those observed for bovinea-lactalbumin and for the Ca²⁺-binding equine lysozyme. At pH4.5, the thermostability of both the apo and Ca²⁺ forms of theA92D human was decreased in comparison with that of native humanlysozyme. In particular, within the apo form of this mutantan a-helix-containing sequence was destabilized. In contrast,at the same pH the thermostability of the apo and Ca²⁺ formsof the M4 mutant lysozyme was increased. The e-ammonium groupof the Lys83 side chain is assumed to be responsible for thestabilization of the apo form of this mutant.     

NMR and ICP spectroscopic analysis of the DNA-binding domain of the Drosophila GCM protein reveals a novel Zn2+-binding motif

Drosophila GCM (glial cell missing) is a novel DNA-binding proteinthat determines the fate of glial precursors from the neuraldefault to glia. The GCM protein contains the functional domainthat is essential for recognition of the upstream sequence ofthe repo gene. In the DNA-binding region of this GCM protein,there is a cysteine-rich region with which divalent metal ionssuch as Zn²⁺ must bind and other proteins belonging to the GCMfamily have a corresponding region. To obtain a more detailedinsight into the structural and functional features of thisDNA-binding region, we have determined the minimal DNA-bindingdomain and obtained inductively coupled plasma atomic emissionspectra and ¹H–¹⁵N, ¹H–¹⁵N–¹³C and ¹¹³Cd²⁺NMR spectra, with or without its specific DNA molecule. Consideringthe results, it was concluded that the minimal DNA-binding domainincludes two Zn²⁺-binding sites, one of which is adjacent tothe interface for DNA binding. Systematic mutational analysesof the conserved cysteine residues in the minimal DNA-bindingdomain revealed that one Zn²⁺-binding site is indispensablefor stabilization of the higher order structure of this DNA-bindingdomain, but that the other is not.     

Lipid-lipase interactions. 2. A new method for the assay of lipase activity

A simplified procedure for the measurement of activity was developed for lipases (EC 3.1.1.3) fromChromobacterium viscosum, Candida rugosa, Aspergillus niger andRhizopus arrhizus. It differs from existing procedures in that olive oil, refined with a bleaching clay, was used as the substrate, periodic sonication was applied to promote efficient emulsification, the hydrolysis time was extended to 1 hr, and no additive such as protective colloids and surfactants were used. The activity was determined arbitrarily for that amount of lipase required to bring about 24% hydrolysis/hr at room temperature Unlike currently used assay procedures, the present method gives results which are highly reproducible with a maximum standard deviation of 2.5% and, more commonly, less than 1.00%.     

Thermal stability and luminescence of novel garnet-type yafsoanite Ca3Zn3(TeO6)2:Sm3+ phosphors for white LEDs

In this study, novel garnet-type yafsoanite tellurate Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphors are successfully synthesized using the traditional high-temperature solid-state reaction. The phase purity of the obtained phosphors is analyzed by X-ray diffraction and Rietveld refinement studies. Morphological variations are also observed with the different concentrations of Sm³⁺ ions substitution, which is analyzed using Scanning Electron Microscopy (SEM). The photoluminescent properties of the phosphors are systematically investigated. Results show that the samples display the strongest emission peak at 612 nm under the near-ultraviolet (n-UV) 409 nm excitation. This peak can be ascribed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphor shows a high color purity, exhibits excellent thermal stability and good color drifting resistance. Furthermore, red and white light-emitting diodes have been successfully prepared. The white light-emitting diodes (w-LEDs) demonstrates a high color rendering index (CRI, R_a) and low correlated color temperature (CCT). This study introduces a new orange-red-emitting phosphor and discusses its application in herb-growth w-LEDs.     

Ca~(2+)、Fe~(3+)沉淀分离HPO_3~(2-)和H_2PO_2~-的研究

采用Ca2+和Fe3+作为沉淀剂分离HPO32-和H2PO2-,研究了Ca2+和Fe3+的加入量、反应温度和陈化时间对分离效果的影响。结果表明,Ca2+作为沉淀剂时,[Ca2+]/[HPO32-]=0.94,处理温度50℃,陈化时间5h条件下HPO23-去除率达到93.1%,而H2PO2-的损失率为1.06%。Fe3+作为沉淀剂时,[Fe3+]/[HPO23-]=1.02,室温下处理,陈化时间6h条件下HPO32-去除率达到75.4%,而H2PO2-的损失率为10.6%。     

Effects of Ca2+-Sr2+ doping on the infrared emissivity of LaCrO3

LaCrO₃ shows excellent thermal stability and good emissivity, and can be used as a potential thermal protection material for hypersonic vehicle. In this study, LaCrO₃ and Ca²⁺-Sr²⁺ doped LaCrO₃ were prepared by solid state reaction at 1400 °C for 2 h. The microstructures of the samples and effects of Ca²⁺-Sr²⁺ doping on the infrared emissivity of LaCrO₃ were studied by XRD, XPS, FT-IR, and UV–VIS–NIR spectrophotometer. The results show that after doping Ca²⁺ and Sr²⁺ ions, the infrared emissivity of all samples has significantly improved at 2.5–10 μm, from 0.61 (minimum value) to above 0.90. In the range of 10–14 μm, the emissivity of pure LaCrO₃ and La_0.8Ca_xSr_0.2-xCrO₃ samples shows a similar trend and all remains above 0.97. Therefore, doping Ca²⁺ and Sr²⁺ can significantly increase the emissivity of LaCrO₃ at 2.5–10 μm, which makes it have a wider application prospect in the field of high temperature thermal protection.     

Ca2+,Al3+对不含Na+硅酸体系聚合行为的影响

为排除Na+对硅酸聚合的影响,用酸解水淬硅酸钙制备了不含金属离子的硅酸溶液及含Ca2+, Al3+的硅酸溶液,研究了加入Ca2+, Al3+对体系聚合行为的影响. 结果表明,加入Ca2+后体系pH值略微降低,加入Al3+后体系pH值显著降低. 初始pH≤2时,Al3+对硅酸聚合起促凝作用,初始pH>2时,Al3+起缓凝作用. Ca2+对硅酸聚合影响不大. 硅酸凝胶后,含Al3+硅酸体系中形成Al?O?Si键,阻碍了凝胶结构水脱附;Ca2+则阻碍凝胶的晶化转变过程,且凝胶中的结构水变少. 不含金属离子、含Ca2+、含Al3+体系的化学式分别为SiO2×0.52H2O, SiO2×0.36H2O, SiO2×1.50H2O.     

Effects of penta-coordinated Al3+ sites and Ni defective sites on Ni/Al2O3 for CO methanation

Engineering sophisticated structure of Al₂O₃ and controlling the structure of counterpart metal active sites remain challenges to achieve a high catalytic-performance in heterogeneous catalysis. Herein, we present a confinement strategy to stabilize homogeneous Ni by penta-coordinated Al³⁺ anchoring sites in Al₂O₃. This approach is involved in using a metal–organic framework as host to load Ni²⁺ ions, by the aim of producing a confined Ni/Al₂O₃ catalyst after a standard calcination. Metal–support interaction between Ni and Al₂O₃ was tailored to be medium to avoid the formation of inactive NiAl₂O₄, which favors the generation of more available Ni active sites accessible to the reactants. The resultant Ni/Al₂O₃ exhibited superior catalytic performance in comparison with the control Ni/Al₂O₃ in CO methanation owing to the presence of defective sites on sufficient Ni⁰ surface. Furthermore, the presence of oxygen vacancies on Al₂O₃ and hydrogen spillover contributed toward excellent coke resistance properties in the reaction.     

Effect of hydrolysis products and Mg2+, Mn2+ and Ca2+ ions on whey lactose hydrolysis and β‐galactosidase stability

BACKGROUND: Enzyme inhibition is one of the constraints of reactions catalysed by enzymes, and information is required on the inhibition mechanisms that affect the process yield. Therefore the aim of the present study was to investigate the effect of hydrolysis products and ions on the hydrolysis of lactose recovered from whey and enzyme inactivation during the reaction. The experiments were carried out in 250 mL of 25 mmol L^?1 phosphate buffer solution using β‐galactosidase from Kluyveromyces marxianus lactis in a batch reactor system. RESULTS : The degree of lactose hydrolysis (%) and the residual enzyme activity (%) in the presence and absence of lactose over time were investigated versus hydrolysate amount, glucose and galactose concentrations and Mg²⁺, Mn²⁺ and Ca²⁺ ion concentrations. The hydrolysis degree decreased with the addition of all hydrolysis products, as enzyme inhibition occurred. The residual enzyme activity increased with the addition of hydrolysate and glucose but decreased with the addition of galactose. It was observed that Mn²⁺ and Mg²⁺ ions activated the enzyme. It was also found that the hydrolysis degree was not affected by the addition of Mn²⁺ ions. On the other hand, the hydrolysis degree decreased with the addition of Ca²⁺ ions, as the enzyme was inactivated. CONCLUSION: Evaluation of the experimental data showed that both β‐galactosidase activity and lactose hydrolysis were affected by the addition of hydrolysis products and ions. Moreover, mathematical models proposed to predict the residual lactose concentration and residual enzyme activity were confirmed by the experimental results. Copyright © 2008 Society of Chemical Industry     

Luminescence properties of Ca2GdNbO6: Sm3+, Eu3+ red phosphors with high quantum yield and excellent thermal stability for WLEDs

A series of Ca₂GdNbO₆: xSm³⁺ (0.01 ≤ x ≤ 0.15) and Ca₂GdNbO₆: 0.03Sm³⁺, yEu³⁺ (0.05 ≤ y ≤ 0.3) phosphors were synthesized by the traditional solid-state sintering process. XRD and the corresponding refinement results indicate that both Sm³⁺ and Eu³⁺ ions are doped successfully into the lattice of Ca₂GdNbO₆. The micro-morphology shows that the elements of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor are evenly distributed in the sample, and the particle size is about 2 μm. The optical properties and fluorescence lifetime of Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors were detailedly studied. The emission peak at ⁵D₀→⁷F₂ (614 nm) is the strongest and emits red light under 406 nm excitation. The increase of Eu³⁺ concentration causes the energy transfers from Sm³⁺ to Eu³⁺ ions, and the transfer efficiency reaches 28.6%. Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor has a quantum yield of about 82.7%, and thermal quenching activation energy is of 0.312 eV. The color coordinate (0.646, 0.352) of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphors is located in the red area. The LED device fabricated based on the above phosphor emit bright white light, and CCT = 5400 K, Ra = 92.8. The results present that Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors potentially find use in the future.     

外加剂对磷铝酸盐水泥中钙、铝析出的影响

用分光光度计等测试技术研究了磷铝酸盐水泥水化时Ca2+,Al3+离子浓度随外加剂掺量不同的变化,并探讨了磷铝酸盐水泥的水化动力学.结果表明:一定掺量的外加剂可调节Ca2+,Al3+离子的析出,改变磷铝酸盐水泥水化加速期的长短,起到了调凝的效果,在磷铝酸盐水泥水化加速期,其水化动力学遵循方程:[1-(1-α)1/3]N=Kt.Ca2+离子的溶出主要受自动催化反应控制,N为1.51～1.67;Al3+离子的溶出则主要受扩散反应控制,N为5.37.     

Conjugation of a zwitterionic polymer with dimethyl chains to lipase significantly increases the enzyme activity and stability

Enzyme-polymer conjugates are complex molecules with great practical significance. This work was designed to develop a novel enzyme-polymer conjugate by covalently coupling a zwitterionic polymer with side dimethyl chains (pID) to Candida rugosa lipase (CRL) via the reaction between the anhydrides of polymer chains with the amino groups of the enzyme. The resulting two CRL-pID conjugates with different pID grafting densities were investigated in term of the catalytic activity, stability and structural changes. In comparison with native CRL, both the CRL conjugates displayed 2.2 times higher activity than the native enzyme, and showed an increase in the maximum reaction rate (V_max) and a decrease in the Michaelis constant (K_m), thus resulting in about three-fold increases in the catalytic efficiency (k_cat/K_m). These are mainly attributed to the activation of lipase by the hydrophobic alky side chains. Moreover, the thermostability and pH tolerance of the lipase conjugates were significantly enhanced due to the stabilizing effect of the zwitterion moieties. For instance, a five-fold increase of the enzyme half-life at 50℃ for the high-pID conjugated CRL was observed. Spectroscopic studies reveal that the pID conjugation protected the enzyme in the changes in its microenvironment and conformation, well correlating with enhanced activity and stability of lipase conjugates. The findings indicate that enzyme conjugation to the zwitterionic polymer is promising for improving enzyme performance and deserves further development.     

Receptor-Dependent and Independent Regulation of Voltage-Gated Ca2+ Channels and Ca2+-Permeable Channels by Endocannabinoids in the Brain

The activity of specific populations of neurons in different brain areas makes decisions regarding proper synaptic transmission, the ability to make adaptations in response to different external signals, as well as the triggering of specific regulatory pathways to sustain neural function. The endocannabinoid system (ECS) appears to be a very important, highly expressed, and active system of control in the central nervous system (CNS). Functionally, it allows the cells to respond quickly to processes that occur during synaptic transmission, but can also induce long-term changes. The endocannabinoids (eCBs) belong to a large family of bioactive lipid mediators that includes amides, esters, and ethers of long-chain polyunsaturated fatty acids. They are produced “on demand” from the precursors located in the membranes, exhibit a short half-life, and play a key role as retrograde messengers. eCBs act mainly through two receptors, CB1R and CB2R, which belong to the G-protein coupled receptor superfamily (GPCRs), but can also exert their action via multiple non-receptor pathways. The action of eCBs depends on Ca²⁺, but eCBs can also regulate downstream Ca²⁺ signaling. In this short review, we focus on the regulation of neuronal calcium channels by the most effective members of eCBs-2-arachidonoylglycerol (2-AG), anandamide (AEA) and originating from AEA-N-arachidonoylglycine (NAGly), to better understand the contribution of ECS to brain function under physiological conditions.     

Synthesis and luminescence properties of reddish-orange-emitting Ca2GdNbO6:Sm3+ phosphors with good thermal stability for high CRI white applications

Novel reddish-orange-emitting Ca₂GdNbO₆:Sm³⁺ phosphors based on the emission of ⁴G_5/2 → ⁶H_9/2 transition at 651 nm with the chromatic coordinate of (0.633, 0.366) were synthesized. The crystal structure and chemical purity were identified in detail. Under the 407 nm excitation, the optimum concentration of Sm³⁺ ion was found to be 5 mol% dominated by the dipole-dipole interaction in the Ca₂GdNbO₆ host material. The color purity of the sample with optimum doping was estimated to be about 78.38%. Besides, the thermal stability was also studied, and it was further found that the emission intensity remained 65.32% at 423 K. The packaged white LED device exhibited excellent CRI and CCT values of 92.43 and 4896 K. Finally, the polydimethylsiloxane film with a stable structure and flexible property was prepared. These above results reveal that novel reddish-orange-emitting Ca₂GdNbO₆:Sm³⁺ phosphors can be applied in high CRI white communication and flexible display applications.     

Crystal Structure and Optical Performance of Al3+ and Ce3+ Codoped Ca3Sc2Si3O12 Green Phosphors for White LEDs

Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce) green phosphors used for white light‐emitting diodes (LEDs) are synthesized and codoped with Al³⁺ via a solid‐state reaction method. The crystal structure and vibrational modes are analyzed by X‐ray diffraction, Fourier transform infrared spectroscopy, and Raman scattering spectroscopy. The energy transfer behavior and optical performance are characterized by photoluminescence and excitation spectra, quantum efficiency, and time‐resolved photoluminescence. The incorporation of Al³⁺ into CSS:Ce can inhibit the formation of the impurity phases Sc₂O₃ and CeO₂, improve crystallinity, and enhance the photoluminescence intensity as well as quantum efficiency. The substitution of Sc³⁺ with Al³⁺ increased the crystal field splitting of Ce³⁺ and resulted in the red shift of photoluminescence. The results show that Ca₃Sc_2?xAl_xSi₃O₁₂:Ce³⁺ has high quantum efficiency, making it a promising green phosphor that can be collocated with a commercial 450 nm blue LED and a red phosphor for solid‐state lighting applications.     

Enhanced luminescence and thermal stability of (Sr,Ca)AlSiN3:Eu2+ via superficial organic carbon modification

The Eu²⁺-activated nitride phosphors have been widely used in solid-state lighting, but the applications in high-power white-light-emitting diodes (wLEDs) field require higher thermal stability of luminescent materials. The oxidation of Eu²⁺ and the damage of nitride host in the Eu²⁺-activated nitride phosphors are the two crucial reasons for the luminescence loss while operating. A superficial organic carbon modification is performed on the red-emitting (Sr,Ca)AlSiN₃:Eu²⁺ phosphor via the incorporation of organic carbon by solution mixing and thermal post-treatment under the N₂-H₂ atmosphere. After the superficial organic carbon modification, the oxidation of Eu²⁺ and the formation of impurity phases on the phosphor surface are effectively reduced. When the superficial organic carbon modified sample was treated in the 2 wt.% sucrose solutions, the relative brightness is strengthened by 2.15%, the thermal quenching characteristic is improved by 8.9% at 300℃, and the aging test results show an excellent thermal stability. All above indicate that the superficial organic carbon modification is a promising technique to enhance the thermal stability of analogous Eu²⁺-activated nirtide phosphors.     

The microstructure and magnetic properties of Ca2+ ion doped GdCrO3

In this paper, the crystal structure, vacancy defect, local electron density and magnetic properties of Gd_1-xCa_xCrO₃ (0 ≤ x ≤ 0.3) polycrystalline samples were investigated systematically. The crystal structural analyses show that all the samples are orthorhombic phase and a structural distortion happens around x = 0.3. Due to the formation of Cr⁴⁺ ions, both the lattice constant and the Cr–O bond length decrease. The results of positron annihilation spectrum reveals that the vacancy defect concentration increases and the local electron structure changes with the introduction of Ca²⁺ ions. The field-cooled (FC) and zero-field cooled (ZFC) curves of Gd_1-xCa_xCrO₃ samples measured under H = 100 Oe exhibits negative magnetization characteristics due to the interaction between Gd³⁺ and Cr³⁺ ions, and the magnetism can be affected by the structural distortion.