Zinc mediation of the binding of human growth hormone to the human prolactin receptor

Human growth hormone (hGH) elicits a diverse set of biological activities including lactation that derives from binding to the prolactin (PRL) receptor. The binding affinity of hGH for the extracellular binding domain of the hPRL receptor (hPRLbp) was increased about 8000-fold by addition of 50 micromolar ZnCl2. Zinc was not required for binding of hGH to the hGH binding protein (hGHbp) or for binding of hPRL to the hPRLbp. Other divalent metal ions (Ca2+, Mg2+, Cu2+, Mn2+, and Co2+) at physiological concentrations did not support such strong binding. Scatchard analysis indicated a stoichiometry of one Zn2+ per hGH.hPRLbp complex. Mutational analysis showed that a cluster of three residues (His18, His21, and Glu174) in hGH and His188 from the hPRLbp (conserved in all PRL receptors but not GH receptors) are probable Zn2+ ligands. This polypeptide hormone.receptor "zinc sandwich" provides a molecular mechanism to explain why nonprimate GHs are not lactogenic and offers a molecular link between zinc deficiency and its association with altered functions of hGH.     

Three-dimensional structure of favin: saccharide binding-cyclic permutation in leguminous lectins

The three-dimensional structure of favin, the glucose- and mannose-binding lectin of Vicia faba (vetch, broad bean), has been determined at a resolution of 2.8 angstroms by molecular replacement. The crystals contain specifically bound glucose and provide the first high-resolution view of specific saccharide binding in a leguminous lectin. The structure is similar to those of concanavalin A (Con A) and green pea lectin; differences from Con A show that minimal changes are needed to accommodate the cyclic permutation in amino acid sequence between the two molecules. The molecule is an ellipsoidal dimer dominated by extensive beta structures. Each protomer contains binding sites for two divalent metal ions (Mn2+ and Ca2+) and a specific saccharide. Glucose is bound by favin in a cleft in the molecular surface and has noncovalent contacts primarily with two peptide loops, one of which contains several metal ion ligands. The specific carbohydrate-binding site is similar to that of Con A in location and general peptide folding, despite several differences in specific amino acid residues.     

叶绿素荧光仪检测重金属离子毒性的研究

[目的]建立一种快速有效的重金属离子毒性检测方法。[方法]选择三角褐指藻(Phaeodactylum tricornutum)为受试生物,采用双通道脉冲振幅调制叶绿素荧光仪(简称ToxY-PAM)检测水中Cu2+、Zn2+、Cr6+3种重金属离子的毒性大小。[结果]三者不同浓度引起的三角褐指藻光合作用抑制率变化基本均在1 h内达到最大值并趋于平稳;3种重金属离子的毒性大小为Cu2+>Zn2+>Cr6+。[结论]ToxY-PAM体积小,携带方便,检测速度快,灵敏度高,适合于重金属离子的现场检测。     

Pb2+·金属离子与牛血清白蛋白的竞争结合平衡研究

[目的]了解Pb2+在牛血清白蛋白上的结合部位。[方法]采用平衡透析方法,研究在模拟生理(pH6.3)条件下Pb2+、金属离子与牛血清白蛋白的结合平衡,并探讨了Pb2+-BSA体系的逐级稳定常数。[结果]Pb2+在BSA上存在2类结合部位,BSA对Pb2+有1.6个强结合部位和6.5个弱结合部位。Pb2+在白蛋白分子中可能存在第1个较强的结合部位,与Zn2+相同。Pb2+在白蛋白分子中可能存在第2个较强的结合部位,与Cu2+相同。Zn2+-Pb2+-BSA三元体系中强结合部位数明显减少,说明Pb2+的优先配位基团在位点siteA。通过非线性最小二乘法拟合Bjerrum方程,确定Pb2+-BSA体系的逐级稳定常数约为104。[结论]该研究可为判断Pb2+在BSA上各结合部位之间的协调性提供参考。     

20×104m3油罐厚钢板焊接裂纹敏感性试验

油罐罐体由钢板焊接而成,焊缝是油罐的薄弱部位,随着钢板厚度的增加,其焊接裂纹敏感性增强.20×104 m3油罐底圈壁板采用的钢板厚度为44 mm,其焊接性能目前尚无工程实例验证,因此,对其焊接裂纹敏感性开展试验研究,以确定合理的焊接工艺参数.斜Y型坡口裂纹试验结果表明:母材和过热区金相组织均为粒状贝氏体,焊缝组织为“先共析铁素体+贝氏体+针状铁素体”,组织未见异常;对于JFE-HITEN610E钢板,采用LB-62UL焊条焊接,焊缝在室温14℃、预热50℃和100℃条件下均表现出较好的抗裂性能.对接接头刚性拘束焊接裂纹试验结果表明:母材和过热区金相组织均为粒状贝氏体,焊缝金相组织为贝氏体,组织未见异常;JFE-HITEN610E钢板和配套的US49/US62A(直径3.2 mm)焊丝+MF33H焊剂,焊缝在室温14℃和预热50.C条件下均表现出较好的抗裂性能.     

二价金属离子与牛血清白蛋白的相互作用

采用荧光光谱法和紫外光谱法研究了5种二价金属离子与牛血清白蛋白（BSA）的相互作用,通过生物大分子猝灭反应机制和结合位点模型研究发现锌离子Zn2+,镍离子Ni2+,钴离子Co2+ 和钙离子Ca2+ 均可导致牛血清白蛋白内源荧光猝灭,Zn2+,Ni2+ 和Co2+ 离子半径处在正常范围,能有效进入牛血清白蛋白结合位点与牛血清白蛋白结合形成超分子配合物,使牛血清白蛋白的二级结构发生改变,主要表现为静态猝灭。Ca2+离子半径较大,受空间位阻影响不能有效进入结合位点对BSA二级结构影响较小,不能与BSA形成配合物,表现为动态猝灭;而Mg2+ 由于大的水合半径阻碍了Mg2+ 与牛血清白蛋白的有效碰撞,使电子或能量的转移受阻,从而导致Mg2+ 对牛血清白蛋白内源荧光无猝灭作用。图3表2参16     

金属离子对噻嗪酮与小牛胸腺DNA相互作用的影响

为探讨噻嗪酮及金属离子共存对非靶标生物遗传毒性的机制,利用紫外、荧光光谱法研究生理条件下噻嗪酮与小牛胸腺DNA(ctDNA)之间的结合作用大小及模式,从分子水平上分析了Cd~(2+)、Co~(2+)、Cu~(2+)、Ni~(2+)存在时对噻嗪酮与ctDNA相互作用的影响。结果表明:噻嗪酮可与ctDNA结合引起噻嗪酮吸收光谱明显红移;可与亚甲基蓝(MB)竞争结合ctDNA,且结合常数K随温度升高呈递减趋势;可与ctDNA以嵌插方式结合使熔点明显升高。环境金属离子的存在不会改变噻嗪酮与ctDNA之间的作用模式,但会影响其结合强弱,低浓度Cu~(2+)、Ni~(2+)可通过离子桥表现出一定的促结合作用,高浓度时则引起DNA结构改变而削弱噻嗪酮与DNA的结合,Co~(2+)、Cd~(2+)能影响DNA分子结构、与噻嗪酮竞争结合位点,导致结合常数下降。     

Crystal structure of a divalent metal ion transporter CorA at 2.9 angstrom resolution

CorA family members are ubiquitously distributed transporters of divalent metal cations and are considered to be the primary Mg2+ transporter of Bacteria and Archaea. We have determined a 2.9 angstrom resolution structure of CorA from Thermotoga maritima that reveals a pentameric cone-shaped protein. Two potential regulatory metal binding sites are found in the N-terminal domain that bind both Mg2+ and Co2+. The structure of CorA supports an efflux system involving dehydration and rehydration of divalent metal ions potentially mediated by a ring of conserved aspartate residues at the cytoplasmic entrance and a carbonyl funnel at the periplasmic side of the pore.     

金属离子-质膜相互作用的分子动力学模拟研究

为研究植物根表质膜与土壤溶液界面上的双电层结构对金属离子在质膜上吸附以及吸收的影响,从分子水平探讨质膜表面电势下金属离子与质膜的相互作用,建立了质膜与金属溶液的界面模型,采用分子动力学方法模拟了质膜界面K~+、Na~+、Ca~(2+)、Mg~(2+)等碱/碱土金属阳离子与Cu~(2+)、Cd~(2+)等重金属离子的结合与分布过程。通过对吸附构型、浓度分布等统计分析,发现阳离子在质膜表面主要与质膜头部的羰基和磷酸基团等极性基团结合;二价阳离子吸附作用比一价阳离子更为强烈,并造成质膜表面电势的反转,直接控制着扩散层中离子的分布特征。分子动力学模拟结果与描述界面双电层结构的Gouy-Chapman-Stern(GCS)经典理论很好地吻合,可以从分子水平预测和解释金属阳离子与质膜相互作用的动态过程。     

重金属胁迫培养对微生物生长的影响

为探究重金属胁迫对微生物生长的影响,以大肠杆菌、枯草芽孢杆菌、啤酒酵母菌和链霉菌为材料,用传统微生物培养方法,研究了不同Hg2+、Cd2+、Cr6+和Pb2+浓度下4种微生物的生长状况。结果表明:低浓度重金属离子对4种微生物生长有促进作用,高浓度有抑制作用,G+较G-对Hg2+和Cd2+更为敏感;4种微生物对重金属离子的敏感性表现为链霉菌>枯草芽胞杆菌>大肠杆菌>啤酒酵母菌,对微生物毒性顺序为Hg2+>Cd2+>Cr6+>Pb2+。     

基于脱氧核酶-等温级联放大耦合的传感体系高灵敏检测水样中铅离子

我们结合等温直链替代反应（SDA）和指数扩增（EXPAR）设计了一种非标记、高灵敏的Pb2+荧光生物传感体系。在 Pb2+存在情况下,底物链被活化的GR-5 DNAzyme快速切割释放引物1。引物1与模板1杂交,并被DNA聚合酶（BSM）延伸形成带限制性内切酶（Nt.BbvCI）的识别序列的双链核苷酸。BSM从Nt.BbvCI切割产生的切口再次延伸形成双链核苷酸,并释放信号G4-DNA片段。G4-DNA片段同时又可以作为模板2的引物,启动指数放大过程,从而释放更多的信号G4-DNA片段。最后,扩增产物G4-DNA与原卟啉锌(ZnPPIX)相互结合从而产生强烈的荧光信号。我们详细优化了多种因素对检测体系的影响,在最优实验条件下,此方法对Pb2+的线性检测范围为 0.1~50 nM,检出限为0.03 nM（S/N=3）,回归方程为 y=288.7x+744.7(y为荧光强度,x为Pb2+浓度)。干扰实验表明,该传感器对Pb2+具有良好的特异性和选择性。该传感体系成功应用于环境水体中 Pb2+含量检测,加标回收率为 94.0%～103.0%。本方法操作简单、选择性好、灵敏度高、有较强的抗干扰性能,可用于环境水样中Pb2+的高灵敏检测。     

Antibiogram and heavy metal resistance of pathogenic bacteria isolated from moribund cage cultured silver catfish (<Emphasis Type="Italic">Pangasius sutchi</Emphasis>) and red hybrid tilapia (<Emphasis Type="Italic">Tilapia</Emphasis> sp.)

Antibiogram and heavy metal resistance patterns of pathogenic bacteria isolated from moribund cage cultured silver catfish (Pangasius sutchi) and red hybrid tilapia (Tilapia sp.) from Sungai Manir, Terengganu, Malaysia were studied and characterized. Sungai Manir is one of the famous rivers in Terengganu for its wide variety of cage cultured freshwater fish. However, to date, the baseline information of antibiogram and heavy metal resistance patterns of the pathogenic bacteria attacking the freshwater fish cultured in Sungai Manir is still lacking. Therefore, this study was carried out, which may be useful for fish farmers as a guideline for fish prophylactic and treatment purposes. Furthermore, present studies also provide information on the safety level of consuming freshwater fish produced from Sungai Manir. In the present study, bacteria were isolated from 100 fish of each moribund silver catfish and red hybrid tilapia using seven media including tryptic soy agar (TSA), Mac Conkey, thiosulphate citrate bile salt (TCBS), eosin methylene blue (EMB), glutamate starch pseudomonas (GSP), xylose lysine deoxycholate (XLD) and Baird Parker media. Identification of bacteria was carried out using conventional biochemical tests and confirmed by commercial bacterial identification kit. Antibiogram of the bacterial isolates against 18 antibiotics; oxolinic acid (2 μg), ampicillin (10 μg), erythromycin (15 μg), furazolidone (15 μg), lincomycin (15 μg), oleandomycin (15 μg), amoxicillin (25 μg), colistin sulphate (25 μg), sulphamethoxazole (25 μg), chloramphenicol (30 μg), doxycycline (30 μg), florfenicol (30 μg), flumequine (30 μg), kanamycin (30 μg), nalidixic acid (30 μg), tetracycline (30 μg), nitrofurantoin (50 μg) and spiramycin (100 μg) was carried out using disk diffusion method, whereas heavy metal resistance patterns (Hg²⁺, Cd²⁺, Cr^{6 +} and Cu²⁺) of the bacterial isolates was determined through twofold agar dilution method. The results showed that the percentage of sensitivity case of the 120 bacterial isolates to the tested antibiotics was 62.7%. This was followed by resistance (26.9%) and intermediary sensitive (10.4%) cases. In terms of the heavy metal resistance patterns, all bacterial isolates were resistant to Hg²⁺ and Cr^{6 +}. However, only 27.8% and 16.7% of the bacterial isolates were sensitive to Cu²⁺ and Cd²⁺, respectively. The multiple antibiotic resistance (MAR) indices indicated that the cage cultured silver catfish and red hybrid tilapia were under high exposure to the tested antibiotic. Overall, the results of the present studies showed that Sungai Manir may be polluted with heavy metal and antibiotic residues.     

土壤pH、有机质和含水氧化物对镉、铅竞争吸附的影响

采用一次平衡法（振荡16h）研究了土壤pH值、有机质和含水氧化物（以晶质氧化铁和非晶质氧化铁为代表）对Cd^2＋、Pb^2＋在水稻土上竞争吸附的影响。结果表明,pH值是影响土壤吸附Cd^2＋、Pb^2＋的主要因素,土壤对金属离子Cd^2＋、Pb^2＋的吸附量随pH值的增大而增加。土壤pH值为5．0和6．5时,对Cd^2＋、Pb^2＋的吸附量分别达到最大。当土壤去除有机质后,土壤对Cd^2＋、Pb^2＋的吸附均降低,与对照相比,分配系数Kd,cd、Kd,pb西分别下降54％～64％和36％-52％;土壤去除非晶质氧化铁后,Kd,cd、Kd,pb与对照相比分别下降32％～45％和15％～33％。有机质和非晶质氧化铁对Cd^2＋、Pb^2＋的选择性为：Pb^2＋〉Cd^2＋.当土壤晶质氧化铁和非晶质氧化铁均去除后．土壤吸附Cd^2＋、Pb^2＋不但未降低,反而有不同程度的增加,Kd,cd、Kd,pb西明显高于对照。     

铅胁迫下不同茶树的生理响应及其亚细胞水平铅分布特性分析

为了分析不同茶树对Pb胁迫的生理响应及其组织亚细胞Pb分布特性,采用盆栽种植法,以铁观音、肉桂两种茶树为材料进行了分析,以期为重金属对茶树毒害机理和茶树对重金属的自我防御研究提供理论依据。结果表明:随着Pb胁迫浓度的增加,茶树叶片超氧化物歧化酶(superoxide dismutase,SOD)、过氧化物酶(peroxidase,POD)、过氧化氢酶(catalase,CAT)活性呈现下降趋势,且肉桂对Pb胁迫的耐受性高于铁观音;相同浓度Pb胁迫下,两种茶树不同组织亚细胞中的总Pb含量显著差异;此外,Pb胁迫下,为降低Pb~(2+)毒害,铁观音茶树表现为提高植物细胞溶质与细胞器中的Pb~(2+)比例,肉桂茶树表现为增加植物细胞壁中的Pb~(2+)结合率。可见,Pb胁迫下,不同茶树的解毒方式存在差异。     

Sequence-specific peptide cleavage catalyzed by an antibody

Monoclonal antibodies have been induced that are capable of catalyzing specific hydrolysis of the Gly-Phe bond of peptide substrates at neutral pH with a metal complex cofactor. The antibodies were produced by immunizing with a Co(III) triethylenetetramine (trien)-peptide hapten. These antibodies as a group are capable of binding trien complexes of not only Co(III) but also of numerous other metals. Six peptides were examined as possible substrates with the antibodies and various metal complexes. Two of these peptides were cleaved by several of the antibodies. One antibody was studied in detail, and cleavage was observed for the substrates with the trien complexes of Zn(II), Ga(III), Fe(III), In(III), Cu(II), Ni(II), Lu(III), Mg(II), or Mn(II) as cofactors. A turnover number of 6 x 10(-4) per second was observed for these substrates. These results demonstrate the feasibility of the use of cofactor-assisted catalysis in an antibody binding site to accomplish difficult chemical transformations.     

葡萄糖氧化酶抑制法检测食品中镉、锡、铅的残留

目前检测重金属使用的国标方法灵敏度高、特异性强,但存在仪器费用高等缺陷。为了建立快速、简便、只要比色即可测定镉、锡、铅的酶抑制法,选择葡萄糖氧化酶(GOD)—辣根过氧化物酶(POD)催化体系,优化了试验条件;利用金属离子对酶活的抑制作用,测定了重金属离子镉、锡、铅对葡萄糖氧化酶活力的影响。所测镉、锡、铅检出限分别为1.3,0.4,1.4μg/mL。研究了检测实际样品中镉、锡、铅的方法,加标回收率分别为92.7%~105.7%;标准差≤1.0%。     

重金属调控非选择性阳离子通道生理功能的研究进展

非选择性阳离子通道（NSCCs）是生物膜上能同时允许不通价态的阳离子通过的多种通道蛋白的集合体,参与了细胞的营养吸收、膨压控制、信号传导等许多生理过程。NSCCs能够快速转运Ca²⁺、K⁺、Mg²⁺等细胞代谢必需的营养元素,也能转运有毒重金属离子。了解重金属离子与NSCCs的互作关系,对于调控植物对污染环境中有害重金属的吸收和转运过程具有重要意义。本文综述了重金属离子类型和浓度影响NSCCs门控机制的研究进展,为探索新型离子通道调控剂及其调控机理提供参考。     

土壤-水稻系统Cd-As同步钝化与吸收阻控研究进展

我国稻田土壤镉-砷(Cd-As)复合污染形势严峻,是实现农田安全利用的难点。相较于其他粮食作物,水稻积累Cd/As的能力更强,对人类健康危害更大,因此,修复Cd-As复合污染稻田土壤,降低稻米Cd/As含量,对保障我国食品安全意义重大。原位钝化技术是目前应用最广泛且治理效率较高的重金属污染土壤修复技术,本文重点阐述了针对稻田土壤Cd-As复合污染的典型钝化剂及其钝化机理,主要包括铁(Fe)+碱性无机材料复合钝化剂、Fe+有机材料复合钝化剂、Fe+有机+碱性无机材料复合钝化剂、有机+碱性无机材料复合钝化剂等;在此基础上,从根际稳定固持和体内运移阻控两方面,探讨原位钝化技术同步降低水稻Cd-As吸收的作用机制。最后,提出未来Cd-As复合钝化剂的研发方向,强调了土壤友好型Fe-Si复合钝化剂可有效从土壤钝化和生理阻隔两方面同步降低Cd/As生物毒害,应用前景广阔。     

Self-nonself discrimination by T cells

The alpha beta T cell receptor (TCR) recognizes antigens that are presented by major histocompatibility complex (MHC)-encoded cell surface molecules by binding to both the antigen and the MHC molecules. Discrimination of self from nonself antigens and MHC molecules is achieved by negative and positive selection of T cells in the thymus: potentially harmful T cells with receptors that bind to self antigens plus self MHC molecules are deleted before they can mount immune responses. In contrast, the maturation of useful T cells with receptors that bind foreign antigens plus self MHC molecules requires the binding of their receptor to MHC molecules on thymic epithelium in the absence of foreign antigen. The binding of the TCR to either class I or class II MHC molecules directs differentiation of the selected cells into either CD4-8+ (killer) or CD4+8- (helper) T cells, respectively.     

Metalloantibodies

A metalloantibody has been constructed with a coordination site for metals in the antigen binding pocket. The Zn(II) binding site from carbonic anhydrase B was used as a model. Three histidine residues have been placed in the light chain complementarity determining regions of a single chain antibody molecule. In contrast to the native protein, the mutant displayed metal-dependent fluorescence-quenching behavior. This response was interpreted as evidence for metal binding in the three-histidine site with relative affinities in the order Cu(II) greater than Zn(II) greater than Cd(II). The presence of metal cofactors in immunoglobulins should facilitate antibody catalysis of redox and hydrolytic reactions.