尖吻蝮蛇毒抗凝血因子(ACF)含量和钙离子含量的定量测定及钙离子结合位点的初步研究

由紫外光谱法测定蛋白质浓度,用ICP测定Ca含量,从而确定一个ACF分子中含一个钙离子.ACF中分子中除一个高亲和性钙结合位点外,至少还有一个低亲和性钙结合位点,只有当过量钙离子存在时,才可能在低亲和性钙结合位点上进一步结合钙离子.Tb³⁺具有比Ca²⁺离子更强的键合ACF能力,能定量结合在ACF中的两个位点上,且能全部取代ACF中Ca²⁺.文中提及的金属离子对ACF的抗凝血活性没有显著的影响.     

尖吻蝮蛇毒抗凝血因子Ⅰ的稀土离子荧光探针研究

稀土离子(Nd3+, Sm3+, Eu3+, Gd3+, Tb3+)对抗凝血因子(ACF Ⅰ)的内源荧光有不同程度的淬灭作用.稀土离子与ACF Ⅰ荧光滴定的结果表明, ACF Ⅰ分子中有两个稀土离子结合位点,稀土离子和钙离子在ACF Ⅰ分子中两个结合位点是共同的竞争结合位点.每个稀土离子与ACF Ⅰ的结合常数K1和K2相接近,说明两个结合位点的结构可能基本一致.不同的稀土离子与ACF Ⅰ之间有相近的结合常数K1或K2,表明ACF Ⅰ分子中的两个结合位点在结构上都有较大的柔性,这种结构柔性为钙离子在ACF Ⅰ与活化凝血因子X的结合反应中所起的激活作用提供了结构基础.     

尖吻蝮蛇毒抗凝血因子Ⅱ的稀土离子荧光探针研究

尖吻蝮蛇毒抗凝血因子(ACF)分子中有两个钙离子结合位点,钙离子对ACF的内源荧光有增强作用,稀土离子(Nd³⁺,Sm³⁺,Eu³⁺,Gd³⁺和Tb³⁺)能取代ACF分子中的钙离子,并对ACF的内源荧光有不同程度的猝灭作用,其中Tb³⁺接受ACF分子中Trp残基传递的能量后,特征荧光增强.稀土离子与ACF荧光滴定表明,ACF分子中有两个稀土离子结合位点,稀土离子和钙离子在ACF分子中两个结合部位是共同的竞争结合部位.ACF与不同稀土离子之间有相近的表观结合常数K₁或K₂.Tb³⁺与RE³⁺(RE=Nd,Sm,Eu或Gd)间线性自由能关系表明,稀土离子与ACF结合时,没有明显的空间效应.ACF分子中的两个结合位点在结构上都有较大的柔性,这种结构柔性为钙离子在ACF与活化凝血因子X的结合反应中起到的促进作用提供了结构基础.     

尖吻蝮蛇毒抗凝血因子I的稀土离子荧光探针研究

稀土离子（Nd^3 ,Sm^3 ,Eu^3 ,Gd^3 ,Tb^3 )对抗凝血因子（ACFI）的内源荧光有不同程度的淬灭作用。稀土离子与ACI I 光滴定的结果表明，ACFI分子中有两个稀土离子结合位点，稀土离子和钙离子在ACF I分子中两个结合位点是共同的竞争结合位点。每个稀土离子与ACF I的结合常数K1和K2相接近，说明两个结合位点的结构可能基本一致。不同的稀土离子与ACF I之间有相近的结合常数K1或K2，表明ACF I分子中的两个结合位点在结构上都有较的柔性，这种结构柔性为钙离子在ACF I与活化凝血因子X的结合反应中所起的激活作用提供了结构基础。     

用钙选择电极和EGTA电位滴定法测定磷矿中的钙

大量磷存在时,用EDTA络合滴定钙是困难的。由于Ga~(2+)-EGTA络合物的稳定常数较大(logKc~+-EGTA=11.0),作者叙述了一种不需添加任何掩蔽剂,以钙电极为指示电极,在pH≥11时,用EGTA电位法测定磷矿中钙的方法。方法简便、快速,相对标准偏差为2％,加入回收率为97—103％。 EGTA滴定Ca~(2+)的滴定曲线:用Ca~(2+)电极为指示电极,饱和甘汞电极为参比电极,EGTA电位滴定Ca~(2+)的试验表明,pH>8,EGTA就能完全络合Ca~(2+);pH<10,到达终点所需的EGTA量     

钙(Ⅱ)对抗凝血因子Ⅱ与活化凝血因子Ⅹ结合反应的影响

皖南尖吻蝮蛇毒抗凝血因子Ⅱ(ACF Ⅱ)不具有酶的活性,通过与活化凝血因子Ⅹ(FXa)结合成1∶1的复合物来延长凝血时间.用高效液相色谱方法,发现ACF Ⅱ与FXa的结合反应依赖于Ca(Ⅱ)浓度,ACF Ⅱ与FXa的最大结合反应所需要的Ca(Ⅱ)浓度约为1×10-3 mol/L.平衡透析的结果表明,ACF Ⅱ分子中有两个不同亲和性的Ca(Ⅱ)结合位点,表观结合常数分别为(1.1±0.3)×105 L/mol和(1.7±0.4)×104 L/mol,ACF Ⅱ与2个Ca(Ⅱ) 结合所需要的Ca(Ⅱ)浓度也约为1×10-3 mol/L.Ca(Ⅱ)对ACF Ⅱ的荧光有增强效应,其最大荧光增强所需要的Ca(Ⅱ)浓度也约为1×10-3 mol/L.由此推测ACF Ⅱ结合上2个Ca(Ⅱ)可能是其与FXa结合的前提条件.     

钙离子与唾液酸相互作用的核磁共振研究

本文通过500MHz质子核磁共振谱研究了二价钙离子与唾液酸的相互作用。在不同Ca~(2+)浓度测量了唾液酸质子的化学位移变化,观察到H_7和H_8以及H_8和H_(9′)质子之间自旋-自旋耦合常数的变化。对这些Ca~(2+)诱导的变化进行分析后发现,唾液酸糖环第六碳位上的侧链构象发生变化,(OH)_7,(OH)_8和(OH)_9羟基中三个氧原子形成一个适合于Ca~(2+)配位的几何空间。因此,唾液酸分子具有一个高亲和力的Ca~(2+)结合部位,其结合常数约为104.72M~(-1)。     

稀土离子对钙调蛋白与单克隆抗体分子识别的影响

分别采用酶联免疫吸附(ELISA)法和荧光标记技术比较了Ca²⁺,La³⁺,Eu³⁺和Yb³⁺离子对钙调蛋白与单克隆抗体2C3之间分子识别的影响.结果表明,金属离子与钙调蛋白作用后会诱导其发生不同的构象变化,并进一步影响到钙调蛋白与单克隆抗体2C3分子之间的结合强度.当钙调蛋白分别与La³⁺,Eu³⁺,Yb³⁺作用后,它与单抗2C3分子之间的解离常数为(26.8±2.5),(21.8±3.4)和(64.8±5.1)nmol/L,而结合Ca²⁺前后的钙调蛋白与单抗分子的解离常数分别为(177.2±2.8)和(157±4.2)nmol/L.这一结果表明,稀土离子诱导钙调蛋白发生的构象变化明显不同于钙离子的作用,这种差异可能是稀土与钙离子对钙调蛋白调控作用表现出差别的原因.     

离子选择电极法测定N,N—二甲基膦酸基甘氨酸与钙的络合物组成和稳定常数

N,N—二甲基膦酸基甘氨酸[N,N—Bis(pheosphonomethyl)glycine,以下简称NBPG]结构式为在农业上作为植物生长调节剂,有明显的增糖增产作用。从化学结构上看,又是很好的络合剂。B.BynozkuHa等人曾研究过与Fe~(3+)、Mn~(2+)、Pb~(2+)的络合反应。本文用钙离子选择电极法测定了NBPG与Ca~(2+)生成络合物的组成和稳定常数;同时测定了NBPG的各级电离常数,为NBPG的开发应用奠定基础。     

钙(Ⅱ)对抗凝血因子Ⅱ与活化凝血因子X结合反应的影响

皖南尖吻蝮蛇毒抗凝血因子Ⅱ(ACFⅡ)不具有酶的活性,通过与活化凝血因子X(FXa)结合成1:1的复合物来延长凝血时间。用高效液相色谱方法,发现ACFⅡ与FXa的结合反应依赖于Ca(Ⅱ)浓度,ACFⅡ与FXa的最大结合反应所需要的CaⅡ浓度约为1×10^-3mol/L。平衡透析的结果表明,ACFⅡ分子中有两个不同亲和性的Ca(Ⅱ)结合位点,表观结合常数分别为(1.1±0.3)×10^5L/mol和(1.7±0.4)×10^4L/mol,ACFⅡ与2个Ca(Ⅱ)结合所需要的Ca(Ⅱ)浓度也约为1×10^-3mol/L。Ca(Ⅱ)对ACFⅡ的荧光有增强效应,其量大荧光增强所需要的Ca(Ⅱ)浓度也约为1×10^-3mol/L。由此推测ACFⅡ结合上2个Ca(Ⅱ)可能性是其与FXa结合的前提条件。     

Fluorescent studies on the binding-Ca2 + in fibrinolytic principle separated from snake venom

By using equilibrium dialysis, atomic absorption spectrometry, fluorescence titration and determination of fluorescence lifetime, it can be determined that each fibrinolytic principle (FP) molecule contains one Ca2+-binding site and one Ca2+ ion, which can be substituted by a Tb3+ ion completely. The intramolecular energy transfer between Tb3+ and the tryptophan (Trp) residue in FP has been investigated through fluorescence spectroscopy. In the FP molecule, the excited energy can transfer from the Trp residue as an energy donor to the Tb3+ ion substituted as an acceptor. The distance between Tb3+ and the Trp residue, approximately 0.38 nm, has been calculated with the experimental data and Forster theory.     

LIQUID-PHASE ADSORPTION KINETICS OF ISOMALTOTRIOSE ON Ca~(2+) EXCHANGE RESIN

1. INTRODUCTION Oligosaccharide is a carbohydrate comprising 2~9 monosaccharide units linked together by glucoside bond. In the digestive system of humankind, there exits no enzyme for the hydrolysis of oligosaccharides. So it can be used by bifidobacteria in large intestine, and lead to some special physiological function [1]. Oligosaccharide exits in many plants, for example, Morinda officinalis, a precious herb growing in south China. In this herb, four oligosaccharides with the funct…     

The quantum cutting of Tb(3+) in Ca(6)Ln(2)Na(2)(PO(4))(6)F(2) (Ln = Gd, La) under VUV-UV excitation: with and without Gd(3+)

The VUV-vis spectroscopic properties of Tb(3+) activated fluoro-apatite phosphors Ca(6)Ln(2-x)Tb(x)Na(2)(PO(4))(6)F(2) (Ln = Gd, La) were studied. The results show that phosphors Ca(6)Gd(2-x)Tb(x)Na(2)(PO(4))(6)F(2) with Gd(3+) ions as sensitizers have intense absorption in the VUV range. The emission color of both phosphors can be tuned from blue to green by changing the doping concentration of Tb(3+) under 172 nm excitation. The visible quantum cutting (QC) via cross relaxation between Tb(3+) ions was observed in cases with and without Gd(3+). Though QC can be realized in phosphors Ca(6)La(2-x)Tb(x)Na(2)(PO(4))(6)F(2), we found that Gd(3+)-containg phosphors have a higher QC efficiency, confirming that the Gd(3+) ion indeed plays an important role during the quantum cutting process. In addition, the energy transfer process from Gd(3+) to Tb(3+) as well as (5)D(3)-(5)D(4) cross relaxation was investigated and discussed in terms of luminescence spectra and decay curves.     

Comparison of Mg~(2+)- and Ca~(2+)-enhancing anaerobic granulation in an expanded granular sludge-bed reactor

The mechanisms responsible for the fast granulation of anaerobic sludge caused by Mg2+ and Ca2+ addition was examined in four lab-scale expanded granular sludge bed(EGSB) reactors. Results indicated that both Mg2+ and Ca2+ accelerated the sludge-granulation process and increased the amount of polysaccharides and proteins in the sludge. Energy dispersive x-ray spectrometry(EDX) analysis revealed that, in a mature granule, both Mg2+ and Ca2+ composed as phosphate and calcium was distributed primarily in the periphery of the granule, while magnesium distributed mainly in the interior. The addition of Mg2+ was more favorable for the nuclei formation, whereas the addition of Ca2+ was more favorable for subgranule growth and maintaining the granules' rigid structure. Results showed that the addition of Mg2+ in the nuclei formation stage and Ca2+ in the granule-growth stage accelerated granulation more than adding only one of them in the granulation process.     

Protonation of the acidic residues in the transmembrane cation-binding sites of the ca(2+) pump

The ionization states of the acidic residues around the Ca2+-binding sites of sarcoplasmic reticulum Ca2+ ATPase are studied by continuum electrostatic calculations and all-atom molecular dynamics simulations with explicit solvent and phospholipids. The two methods consistently indicate that Glu58 and Glu908 are protonated at neutral pH. The Ca2+ coordination and the H-bonds formed by the protonation of Glu58 and Glu908 are stable in an MD simulation, whereas the H-bonds are disrupted and the Ca2+ coordination geometry is severely altered in another simulation treating these residues unprotonated. The results clearly indicate that the H-bonds formed by protonation of Glu58 and Glu908 provide extra stability for the Ca2+-binding sites of Ca2+ ATPase.     

钙(Ⅱ)对尖吻蝮蛇毒抗凝血因子Ⅰ的抗凝血活性的影响

皖南尖吻蝮蛇毒抗凝血因子Ⅰ(ACFⅠ)不具有酶的活性,通过与活化凝血因子X(FXa)结合成1l的复合物来延长凝血时间。用高效液相色谱分析方法,发现ACFⅠ与FXa的结合反应依赖于Ca     

Unusual Luminescence of Ca8[Al12O24]（WO4）2： Tb^3＋

The luminescence properties of aluminate sodalite Ca8[Al12024](WO4)2 (CAW) undoped and doped with Th^3 are reported and discussed. At room temperature the emission of tetrahedral WO4^2- in CAW showed an abnormally small Stokes shift (9060 cm^-1), which is related to the crystal structure of CAW. A strong absorption band in the excitation spectrum of the Th^3 -activated CAW is ascribed to the absorption of the charge transfer state Th^4 -W^5 , into which the excitation resulted in the efficient emission from the ^5D4 level of Tb^3 , but not from the ^5D3 level.