共查询到20条相似文献，搜索用时 750 毫秒
1.
The hydrolysis of methyl phosphate bound to the triethylenetetramine-cobalt(III) ion is much faster than the hydrolysis of either dimethyl phosphate bound to the same cation or methyl phosphate bound to the pentamminecobalt-(III) ion. The rate enhancement is attributed to bidenate coordination of the methyl phosphate. This feature suggests a pseudorotation mechanism analogous to that proposed by Westheimer for the hydrolysis of ethylene methyl phosphate. Stabilization of bidentate coordination might play a role in metal ion activation of phosphate-transfer enzymes. 相似文献
2.
3.
Acetyl phosphate and 1,3-diphosphoglycerate react with glyceraldehyde-3-phosphate dehydrogenase to form relatively stable enzyme substrate compounds. These compounds appear to be thiol esters, and their properties indicate that they are intermediates in the catalytic activity of the enzyme: they undergo hydrolysis and arsenolysis in the presence of DPN and are reduced by DPNH to form aldehydes. These results are in agreement with the mechanism previously proposed for the oxidation of aldehydes in which a thiol ester formed on the enzyme, with concomitant reduction of DPN, is split in the presence of phosphate to acyl phosphate and regenerated enzyme. 相似文献
4.
氢离子焦磷酸化酶(H~+-PPase)是一类H~+转运蛋白,它以焦磷酸(PPi)水解底物,水解PPi产生的自由能与H~+跨膜转运相藕联,将细胞质中的H~+泵入液泡中,建立跨液泡膜电化学梯度,形成质子驱动力,为无机离子及其他溶质进出液泡提供动力,有利于植物维持细胞离子平衡和渗透平衡,增强植物的抗逆性。基于前期对披碱草(Elymus dahuricus)H~+-PPase基因Ed HP1克隆的基础,对其表达谱及基因功能进行了进一步研究。结果表明,通过Northern blot分析发现,该基因在披碱草中受干旱、低温非生物胁迫诱导表达。通过对转Ed HP1基因烟草在干旱、低温环境下的功能分析发现,过表达Ed HP1基因可以提高转基因烟草对干旱、冷胁迫的抗性。 相似文献
5.
Diaz J Ingall E Benitez-Nelson C Paterson D de Jonge MD McNulty I Brandes JA 《Science (New York, N.Y.)》2008,320(5876):652-655
The in situ or authigenic formation of calcium phosphate minerals in marine sediments is a major sink for the vital nutrient phosphorus. However, because typical sediment chemistry is not kinetically conducive to the precipitation of these minerals, the mechanism behind their formation has remained a fundamental mystery. Here, we present evidence from high-sensitivity x-ray and electrodialysis techniques to describe a mechanism by which abundant diatom-derived polyphosphates play a critical role in the formation of calcium phosphate minerals in marine sediments. This mechanism can explain the puzzlingly dispersed distribution of calcium phosphate minerals observed in marine sediments worldwide. 相似文献
6.
Some of the most remarkable fossils preserve cellular details of soft tissues. In many of these, the tissues have been replaced by calcium phosphate. This process has been assumed to require elevated concentrations of phosphate in sediment pore waters. In decay experiments modern shrimps became partially mineralized in amorphous calcium phosphate, preserving cellular details of muscle tissue, particularly in a system closed to oxygen. The source for the formation of calcium phosphate was the shrimp itself. Mineralization, which was accompanied by a drop in pH, commenced within 2 weeks and increased in extent for at least 4 to 8 weeks. This mechanism halts the normal loss of detail of soft-tissue morphology before fossilization. Similar closed conditions would prevail where organisms are rapidly overgrown by microbial mats. 相似文献
7.
Tritiated digoxin binding to (Na+ + K+)-activated adenosine triphosphatase: possible allosteric site 总被引：9，自引：0，他引：9
Tritiated H(3)-digoxin specifically binds to a cardiac (Na(+) + K(+))-activated adenosine triphosphatase. In the presence of adenosine triphosphate and other nucleoside di- and triphosphates, binding is stimulated by sodium ion, the apparent rate constant being similar to that reported for phosphorus-32 incorporation from adenosine triphosphate and for the adenosine triphosphatase activity. In the presence of magnesium, manganese, inorganic phosphate, or other ions, sodium ion inhibits binding. The data support an allosteric type of sodium-potassium ion pump. 相似文献
8.
为解析钙离子胁迫对槲蕨孢子体叶片生长影响的生理机制,以两年生槲蕨孢子体叶为实验材料,观察了钙离子胁迫对孢子体叶的影响。将温室培养的两年生槲蕨植株移栽至直径18.5 cm的花盆中,以蛭石为基质,置于光照培养箱,浇施霍格兰德营养液7d后,分别浇施含有不同钙离子含量的霍格兰德营养液,处理14天,根据槲蕨叶片的形态变化确定处理浓度。取0、600、1200 mmol?L-1钙离子浓度处理的槲蕨叶片测定脯氨酸含量、甜菜碱含量、电导率含量、超氧阴离子含量、过氧化氢含量、抗坏血酸过氧化物酶活性、单脱氢抗坏血酸还原酶活性、脱氢抗坏血酸还原酶活性和谷胱甘肽还原酶活性。结果显示：槲蕨孢子体叶的脯氨酸含量随着钙离子处理浓度的逐渐增加逐渐升高,而甜菜碱含量在1200 mmol?L-1显著升高;电导率、超氧阴离子和过氧化氢的含量随着处理浓度的升高而增加;抗坏血酸过氧化物酶、单脱氢抗坏血酸还原酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶活性随着处理浓度的增加而增强;表明钙离子浓度在1200 mmol?L-1以下时主要产生渗透胁迫作用。 相似文献
9.
A tight coupling between adenosine triphosphate (ATP) hydrolysis and vectorial ion transport has to be maintained by ATP-consuming ion pumps. We report two crystal structures of Ca2+-bound sarco(endo)plasmic reticulum Ca2+-adenosine triphosphatase (SERCA) at 2.6 and 2.9 angstrom resolution in complex with (i) a nonhydrolyzable ATP analog [adenosine (beta-gamma methylene)-triphosphate] and (ii) adenosine diphosphate plus aluminum fluoride. SERCA reacts with ATP by an associative mechanism mediated by two Mg2+ ions to form an aspartyl-phosphorylated intermediate state (Ca2-E1 approximately P). The conformational changes that accompany the reaction with ATP pull the transmembrane helices 1 and 2 and close a cytosolic entrance for Ca2+, thereby preventing backflow before Ca2+ is released on the other side of the membrane. 相似文献
10.
Loss of a parathyroid hormone-sensitive component of phosphate transport in X-linked hypophosphatemia 总被引：15，自引：0，他引：15
Mutant hemizygotes with X-linked hypophosphatemia lack a parathyroid hormone-sensitive component of inorganic phosphate transport in kidney; female heterozygotes retain a variable proportion of this type of transport. The residual mechanism for reabsorption in affected males allows inorganic phosphate efflux from the kidney to urine so that net "secretion" is sometimes observed; the latter is directly proportional to the serum concentration of inorganic phosphate. Calcium acts on the kidney tubule to enhance net reabsorption by this component of inorganic phosphate transport. 相似文献
11.
腺苷三磷酸结合盒转运蛋白（ATP-binding cassette transporter,ABC转运蛋白）是一类大量存在于原核生物及真核生物的跨膜转运蛋白,其种类繁多、家族庞大且功能多样,主要功能是利用ATP水解产生的能量将底物进行逆浓度梯度跨膜运输,同时还参与抗原传递、信号传导和细胞解毒等很多重要的生物生理过程。综述了ABC转运蛋白的结构特点、跨膜吸收机制及影响因素,为研究ABC转运蛋白跨膜吸收转运养分离子及其抵抗非生物逆境胁迫提供理论支撑和研究思路。 相似文献
12.
13.
Slaven Jurić Edyta Đermić Snježana Topolovec-Pintarić Marta Bedek Marko Vinceković 《农业科学学报》2019,18(11):2534-2548
Novel agroformulations for simultaneous delivery of chemical and biologically active agents to the plants were prepared by encapsulation of Trichoderma viride spores in calcium alginate microspheres. The impact of calcium ions concentration on the viability and sporulation of T. viride spores as well as on the microsphere important physicochemical properties were investigated. Intermolecular interactions in microspheres are complex including mainly hydrogen bonds and electrostatic interactions. T. viride germination inside matrix and germ tubes penetration out of microspheres revealed calcium alginate microspheres provide a supportive environment for T. viride growth. Differences in physicochemical properties and bioactive agents release behaviour from microspheres were ascribed to the changes in microsphere structure. Fitting to Korsmeyer-Peppas empirical model revealed the underlying T. viride release mechanism as anomalous transport kinetics (a combination of two diffusion mechanisms and the Type II transport (polymer swelling and relaxation of the polymeric matrix)). The increasing amount of T. viride spores in the surrounding medium is closely related to the release from microspheres and germination. The rate controlling mechanism of calcium release is Fickian diffusion. A decrease in the release rate with increasing calcium ion concentrations is in accordance with the calcium ions effect on the strength of the alginate network structure. T. viride germination inside microsphere diminished the amount of released calcium ions and slowed release kinetics in comparison with microspheres prepared without T. viride. The results indicated investigated agroformulations have a great potential to be used for plant protection and nutrition. 相似文献
14.
生物质炭、有机肥和钙镁磷肥对三七(Panax Notoginseng) Cd含量的影响 总被引：1，自引：0，他引：1
选择生物质炭、钙镁磷肥、有机肥三种改良剂,在云南三七主产区进行田间试验,比较不同改良剂对降低五加科人参属三七(Panax Notoginseng)Cd含量的效果。结果表明,生物质炭和钙镁磷肥处理均显著降低了三七主根、剪口、茎、叶的Cd含量,降低幅度分别为25.4%~43.6%、40.2%~40.9%、34.3%~51.2%和33.0%~33.5%,且生物质炭、钙镁磷肥处理下三七主根干重较对照分别显著提高48.7%和50.4%;生物质炭和钙镁磷肥处理土壤有效Cd含量分别减少56.1%和58.1%,表明生物质炭和钙镁磷肥能有效降低土壤Cd生物有效性、抑制三七Cd吸收。这与生物质炭和钙镁磷肥处理通过降低土壤酸性、提高土壤CEC及有机质含量有关。有机肥处理三七植株生物量和三七各部位Cd含量与对照相比均无显著差异。此外,生物质炭和钙镁磷肥处理显著降低了三七主根、剪口、茎、叶Cd的富集系数(Accumulation coefficient,AF),对三七Cd转移系数(Transfer coefficient,TF)影响则不显著,而有机肥处理对三七Cd的AF与TF均无影响;各处理三七须根Cd的AF在2.84~4.64之间,显著高于其他部位,而三七主根、剪口、茎、叶等部位Cd的AF和TF均小于1,表明三七须根对土壤Cd富集能力较强而转移能力较差,Cd易集中于三七地下部,Cd污染土壤中施用生物质炭与钙镁磷肥能有效降低Cd在三七体内的富集。 相似文献
15.
Osteoclastic bone resorption by a polarized vacuolar proton pump 总被引：42，自引：0，他引：42
Bone resorption depends on the formation, by osteoclasts, of an acidic extracellular compartment wherein matrix is degraded. The mechanism by which osteoclasts transport protons into that resorptive microenvironment was identified by means of adenosine triphosphate-dependent weak base accumulation in isolated osteoclast membrane vesicles, which exhibited substrate and inhibition properties characteristic of the vacuolar, electrogenic H+-transporting adenosine triphosphatase (H+-ATPase). Identify of the proton pump was confirmed by immunoblot of osteoclast membrane proteins probed with antibody to vacuolar H+-ATPase isolated from bovine kidney. The osteoclast's H+-ATPase was immunocytochemically localized to the cell-bone attachment site. Immunoelectron microscopy showed that the H+-ATPase was present in the ruffled membrane, the resorptive organ of the cell. 相似文献
16.
The transport of ions across the membranes of cells and organelles is a prerequisite for many of life's processes. Transport often involves very precise selectivity for specific ions. Recently, atomic-resolution structures have been determined for channels or pumps that are selective for sodium, potassium, calcium, and chloride: four of the most abundant ions in biology. From these structures we can begin to understand the principles of selective ion transport in terms of the architecture and detailed chemistry of the ion conduction pathways. 相似文献
17.
Chang Q Hoefs S van der Kemp AW Topala CN Bindels RJ Hoenderop JG 《Science (New York, N.Y.)》2005,310(5747):490-493
Blood calcium concentration is maintained within a narrow range despite large variations in dietary input and body demand. The Transient Receptor Potential ion channel TRPV5 has been implicated in this process. We report here that TRPV5 is stimulated by the mammalian hormone klotho. Klotho, a beta-glucuronidase, hydrolyzes extracellular sugar residues on TRPV5, entrapping the channel in the plasma membrane. This maintains durable calcium channel activity and membrane calcium permeability in kidney. Thus, klotho activates a cell surface channel by hydrolysis of its extracellular N-linked oligosaccharides. 相似文献
18.
J Kellosalo T Kajander K Kogan K Pokharel A Goldman 《Science (New York, N.Y.)》2012,337(6093):473-476
Membrane-integral pyrophosphatases (M-PPases) are crucial for the survival of plants, bacteria, and protozoan parasites. They couple pyrophosphate hydrolysis or synthesis to Na(+) or H(+) pumping. The 2.6-angstrom structure of Thermotoga maritima M-PPase in the resting state reveals a previously unknown solution for ion pumping. The hydrolytic center, 20 angstroms above the membrane, is coupled to the gate formed by the conserved Asp(243), Glu(246), and Lys(707) by an unusual "coupling funnel" of six α helices. Comparison with our 4.0-angstrom resolution structure of the product complex suggests that helix 12 slides down upon substrate binding to open the gate by a simple binding-change mechanism. Below the gate, four helices form the exit channel. Superimposing helices 3 to 6, 9 to 12, and 13 to 16 suggests that M-PPases arose through gene triplication. 相似文献
19.
Imaging elemental distribution and ion transport in cultured cells with ion microscopy 总被引：2，自引：0，他引：2
Both elemental distribution and ion transport in cultured cells have been imaged by ion microscopy. Morphological and chemical information was obtained with a spatial resolution of approximately 0.5 micron for sodium, potassium, calcium, and magnesium in freeze-fixed, cryofractured, and freeze-dried normal rat kidney cells and Chinese hamster ovary cells. Ion transport was successfully demonstrated by imaging Na+-K+ fluxes after the inhibition of Na+- and K+ -dependent adenosine triphosphatase with ouabain. This method allows measurements of elemental (isotopic) distribution to be related to cell morphology, thereby providing the means for studying ion distribution and ion transport under different physiological, pathological, and toxicological conditions in cell culture systems. 相似文献
20.
黄牛肉中钙激活酶系统的动力学性质#br# 总被引：1，自引：1，他引：0
【目的】阐明牛肉中钙激活酶系统的主要动力学特征。【方法】通过温度、时间、Ca2+浓度、反应时间、酶量、底物浓度等的变化,分析µ-钙激活酶,m-钙激活酶和钙激活酶抑制蛋白的动力学特性。【结果】随冷冻温度的升高和贮存时间的延长,钙激活酶系统活性都逐步降低,但冷冻处理可以显著降低钙激活酶抑制蛋白的活性,而钙激活酶对冷冻处理不太敏感;µ-钙激活酶达到最大活性一半时所需的Ca2+浓度为50 µmol•L-1,m-钙激活酶为320 µmol•L-1;在测定钙激活酶活性时,反应时间应控制在60 min以内,酶活单位应小于0.45;在以酪蛋白为底物时,m-钙激活酶的Km值为3.185 mg•mL-1,Vmax为0.015 U•min-1,而µ-钙激活酶的Km值为5.320 mg•mL-1,Vmax为0.017 U•min-1。【结论】钙激活酶系统活性受贮藏温度和时间、Ca2+浓度、酶促反应时间、酶量、底物浓度影响明显。 相似文献