共查询到20条相似文献，搜索用时 31 毫秒
1.
Op den Camp R Streng A De Mita S Cao Q Polone E Liu W Ammiraju JS Kudrna D Wing R Untergasser A Bisseling T Geurts R 《Science (New York, N.Y.)》2011,331(6019):909-912
Rhizobium-root nodule symbiosis is generally considered to be unique for legumes. However, there is one exception, and that is Parasponia. In this nonlegume, the rhizobial nodule symbiosis evolved independently and is, as in legumes, induced by rhizobium Nod factors. We used Parasponia andersonii to identify genetic constraints underlying evolution of Nod factor signaling. Part of the signaling cascade, downstream of Nod factor perception, has been recruited from the more-ancient arbuscular endomycorrhizal symbiosis. However, legume Nod factor receptors that activate this common signaling pathway are not essential for arbuscular endomycorrhizae. Here, we show that in Parasponia a single Nod factor-like receptor is indispensable for both symbiotic interactions. Therefore, we conclude that the Nod factor perception mechanism also is recruited from the widespread endomycorrhizal symbiosis. 相似文献
2.
An oxygen-binding hemoglobin localized in the nerves of Tellina alternata (Bivalvia) required 30 minutes to unload oxygen when excised nerves were exposed to pure nitrogen. Neural excitability under these conditions could be sustained only until deoxygenation of the hemoglobin was complete. When the oxygen-combining function of the hemoglobin was abolished with carbon monoxide, the neural excitability ceased within a few minutes of oxygen removal, a response identical to that of hemoglobinless homologous nerves of other bivalves. These results demonstrate that aerobic activity can be supported by the oxygen stored on hemoglobin in microscopic tissues for a considerable time under anoxic conditions. 相似文献
3.
A heterodont bivalve mollusk Calyptogena magnifica, from the East Pacific Rise and the Galápagos Rift hydrothermal vent areas, contains abundant hemoglobin in circulating erythrocytes. No other known heterodont clam contains a circulating intracellular hemoglobin. The hemoglobin is tetrameric and has a relatively high oxygen affinity, which varies only slightly between 2 degrees and 10 degrees C. The presence of hemoglobin in the clam may facilitate the transport of oxygen to be used in chemoautotrophic hydrogen sulfide metabolism. 相似文献
4.
COLLINS RE 《Science (New York, N.Y.)》1961,133(3464):1593-1594
A mathematical theory is developed to explain the observed enhancement of oxygen transport through solutions by hemoglobin. At high partial pressures of oxygen, ordinary diffusion through the solvent accounts for all transport of oxygen, but at low partial pressures the transport may be increased many fold by the presence of hemoglobin. This phenomenon is explained and the possible role of this phenomenon in living organisms is discussed. The theory also indicates a new method of determining dissociation curves from diffusion experiments. 相似文献
5.
B Sullivan 《Science (New York, N.Y.)》1967,157(794):1308-1310
Natrix taxispilota hemoglobin has a very high oxygen affinity which depends upon pH in an unusual manner. The oxygen affinity increases slightly upon protein dilution, but the pK's of the Bohr groups are unchanged. Oxidation promotes hemoglobin polymerization, which can be inhibited by prior treatment with iodoacetamide. Reaction with iodoacetamide also causes a slight increase in the oxygen affinity, no change in the pK's of the Bohr groups, and a drastic reduction in heme-heme interaction. 相似文献
6.
Delay time of hemoglobin S polymerization prevents most cells from sickling in vivo 总被引：10，自引：0，他引：10
A laser photolysis technique has been developed to assess the quantitative significance of the delay time of hemoglobin S gelation to the pathophysiology of sickle cell disease. Changes in the saturation of hemoglobin S with carbon monoxide produced by varying the intensity of a photolytic laser beam were used to simulate changes in the saturation of oxyhemoglobin S produced by variations in oxygen pressure. The presence of polymer at steady-state saturation with carbon monoxide was determined by measurement of the kinetics of gelation after complete photodissociation. The kinetics are a very sensitive probe for polymer since small amounts of polymerized hemoglobin increase the rate of nucleation sufficiently to eliminate the delay period. First, the equilibrium gelation properties of partially photodissociated carbonmonoxyhemoglobin S were shown to be the same as partially oxygenated hemoglobin S, and the method was then used to determine the effect of saturation on the formation and disappearance of polymers in individual sickle cells. The saturation at which polymers first formed upon deoxygenation was much lower than the saturation at which polymers disappeared upon reoxygenation. The results indicate that at venous saturations with oxygen, gelation takes place in most cells at equilibrium, but is prevented from occurring in vivo because the delay times are sufficiently long that most cells return to the lungs and are reoxygenated before polymerization has begun. 相似文献
7.
Electron exchange involving the valence states of iron occurs via water bridges. Molecular oxygen reversibly displaces the sole coordinated water of the ferrous iron in hemoglobin, and, in the absence of this ready path for electron transfer, the oxygen is transported without oxidation of the ferrous iron of hemoglobin. 相似文献
8.
Hyperbaric nitrogen at a pressure of 100 atmospheres increases significantly the affinity of erythrocytic hemoglobin for oxygen. This results in oxygen dissociation curves which are shifted to lower than normal oxygen partial pressures. The pressure effect is completely reversible and can therefore be observed only during exposure of the blood cells to the hyperbaric gas. 相似文献
9.
Cat hemoglobin has a lower cooperativity and oxygen affinity than most mammalian hemoglobins. In contrast to the usual invariance of cooperativity with pH, a rise in cooperativity with pH is predicted by the allosteric model for low-affinity hemoglobins. Such a pH-dependent cooperativity for cat hemoglobin has been found. 相似文献
10.
Phenylhydrazine-induced anemia in the domestic cat results in an increase in minor, high oxygen affinity hemoglobin B components and an accompanying decrease in the major, low affinity B component. This change is accompanied by an unusually large increase in erythrocytic adenosine triphosphate and 2,3-diphosphoglycerate, a slight decrease in the oxygen affinity of whole blood, and a large decrease in the Hill constant. 相似文献
11.
Extracellular hemoglobin in the whole blood of Riftia pachyptila has a high oxygen affinity (P50 = 1.8 millimeters of mercury at 3 degrees C), a moderate decrease in oxygen affinity at higher temperatures (P50 = 2.7 millimeters of mercury at 14 degrees C), a small effect of carbon dioxide on oxygen affinity (Delta log P50/Delta pH =-0.12), and a high oxygen carrying capacity (up to 11 milliliters of oxygen per 100 milliliters of blood). These characteristics are compatible with the high oxygen demand of chemoautotrophic metabolism in the variable vent environment. 相似文献
12.
Regulation of erythrocyte cation and water content in sickle cell anemia 总被引：25，自引：0，他引：25
The pathophysiological events in sickle cell disease are critically dependent on the intracellular concentration of hemoglobin S, which varies inversely with cell cation and water content. Erythrocytes of SS homozygotes exposed to oxygen or carbon monoxide decrease their potassium and water content through a pathway for potassium transport that is activated by both cell swelling and decrease in internal pH. This pathway is not inhibited by ouabain either with or without bumetanide. When SS erythrocytes were separated according to density, the pH- and volume-dependent potassium transport was greatest in the least dense fraction and was reduced in the densest cells. This pathway, which does not depend on polymerization of sickle hemoglobin, may be important in regulating the cation and water content of SS erythrocytes. 相似文献
13.
Survival at extreme altitude: protective effect of increased hemoglobin-oxygen affinity 总被引：3，自引：0，他引：3
Decreased hemoglobin-oxygen affinity is thought to be of adaptive value to humans and nonindigenous animals at high altitude. To test this, hemoglobin-oxygen affinity was modified by carbamoylation of hemoglobin in rats. Exposure of control (low oxygen affinity) and experimental (high oxygen affinity) animals to a pressure equivalent to high altitude revealed that increased, rather than decreased, hemoglobin-oxygen affinity will permit survival at greatly reduced environmental oxygen pressures. 相似文献
14.
Oxygen binding in cyanmet hybrid and normal hemoglobins: applicability of sequential and two-state concerted models 总被引：1，自引：0，他引：1
A P Minton 《Science (New York, N.Y.)》1974,184(136):577-579
The cyanmet hybrid hemoglobins alpha(2)beta(+CN)(2) and alpha(+CN)(2)beta(2) are widely held to be similar or equivalent in structure and subunit interactions to the partially oxygen-liganded species alpha(2)(beta * O(2))(2) and (alpha * O(2))(2)beta(2), respectively. An analysis of precise data on oxygen binding to the cyanmet hybrids and normal hemoglobin shows that if this is the case, then cooperative ligand binding in hemoglobin is more properly described by some model of the sequential type than by any twostate concerted model. 相似文献
15.
A kinetic model based on allosteric mechanisms of cooperativity fits the experimentally observed phosphate dependence of hemoglobin reactions. Subunit inequivalence is found to be important in analyzing hemoglobin kinetics. The observed increase in the rate of deoxygenation in the presence of organic phosphates is primarily related to the increased rate of dissociation of the second oxygen molecule. 相似文献
16.
采用室内培养实验方法,对水稻幼苗的多项生理生化指标进行了测定。结果表明,随着除草剂苯噻草胺浓度的升高,水稻株高变矮,根长缩短;蛋白质、叶绿素和GSH含量应激升高。活性氧·O-2、H2O2和膜脂过氧化产物MDA的含量增加,组织自氧化速率增大,表明苯噻草胺对水稻幼苗的毒害作用主要是破坏了体内的活性氧平衡。水稻叶片中的CAT酶,根中的SOD和POD酶对苯噻草胺的浓度比较敏感。SOD与MDA含量呈显著正相关,提示了抗氧化酶清除活性氧的作用滞后于活性氧对膜脂过氧化的诱导作用。 相似文献
17.
F A Oski L D Miller M Delivoria-Papadopoulos J H Manchester J C Shelburn 《Science (New York, N.Y.)》1972,175(28):1372-1373
Propranolol, a blocking agent for the beta adrenergic receptor, produces a redistribution of 2,3-diphosphoglycerate in the red cell. At concentrations of 3.3 x10(-5)M, 2,3-diphosphoglycerate in the red cell membrane becomes unbound in vitro. The administration of propranolol to hunmns produces similar changes and results in a decrease in the affinity of hemoglobin for oxygen. 相似文献
18.
Synthesis of functional human hemoglobin in transgenic mice 总被引：18，自引：0，他引：18
R R Behringer T M Ryan M P Reilly T Asakura R D Palmiter R L Brinster T M Townes 《Science (New York, N.Y.)》1989,245(4921):971-973
Human alpha- and beta-globin genes were separately fused downstream of two erythroid-specific deoxyribonuclease (DNase) I super-hypersensitive sites that are normally located 50 kilobases upstream of the human beta-globin gene. These two constructs were coinjected into fertilized mouse eggs, and expression was analyzed in transgenic animals that developed. Mice that had intact copies of the transgenes expressed high levels of correctly initiated human alpha- and beta-globin messenger RNA specifically in erythroid tissue. An authentic human hemoglobin was formed in adult erythrocytes that when purified had an oxygen equilibrium curve identical to the curve of native human hemoglobin A (Hb A). Thus, functional human hemoglobin can be synthesized in transgenic mice. This provides a foundation for production of mouse models of human hemoglobinopathies such as sickle cell disease. 相似文献
19.
20.
[目的]研究不同运行模式人工湿地中溶解氧与净化效率的关系。[方法]采用在线试验模型和现场监测分析方法,研究不同运行模式的有/无植物人工湿地对污水的净化效果与溶解氧的关系。[结果]连续运行的人工湿地上有无植物对有机物和氮磷污染物的净化效果没有明显影响,间隔运行的人工湿地上有无植物对污水中CODCr、NH4+-N、TN的平均去除率存在显著性差异,种有植物间隔运行的人工湿地对CODCr、NH4+-N、TN的平均去除率比连续运行的人工湿地和没有种植植物间隔运行的人工湿地高。人工湿地系统对污水中CODCr、NH4+-N、TN的净化效率在昼间较高、夜间较低,污染物净化效果与溶解氧之间存在着正相关的关系。人工湿地的前置单元增氧有利于改善后置湿地单元的溶氧环境条件,可以提高人工湿地系统净化污染物的能力。种植植物的人工湿地系统宜在昼间运行,利用好植物的光合增氧潜力,则可表现出良好的净化污染物的效果。[结论]该研究为氧化塘-人工湿地系统的运行管理提供了科学依据。 相似文献