Protein phosphatases: properties and role in cellular regulation

Protein phosphorylation is a principal regulatory mechanism in the control of almost all cellular processes. The nature of the protein phosphatases that participate in these reactions has been a subject of controversy. Four enzymes, termed protein phosphatases 1, 2A, 2B, and 2C, account for virtually all of the phosphatase activity toward phosphoproteins involved in controlling glycogen metabolism, glycolysis, gluconeogenesis, fatty acid synthesis, cholesterol synthesis, and protein synthesis. The properties, physiological roles, and mechanisms for regulating the four protein phosphatases are reviewed.     

Intestinal calcium transport: the role of sodium

The role of sodium in intestinal calcium transport was investigated in everted rat intestine. Ethacrynic acid, but not ouabain, inhibited calcium transport. However, ouabain did inhibit net water transport and, therefore, sodium transport, establishing the dissociation of the two transport processes. In addition to a magnesium-dependent adenosine triphosphatase (activated by sodium and potassium), a phosphatase dependent on sodium and calcium was localized to the lateral and basal membrane fractions of the mucosal cell. Activity of the latter phosphatase, similar to calcium transport in intact tissue, was inhibited by ethacrynic acid and not by ouabain. Sodium, therefore, may participate in the calcium transport process by activating an enzyme complex, dependent on adenosine triphosphate, that mediates calcium transport.     

Brain serotonin content: physiological regulation by plasma neutral amino acids

When plasma tryptophan is elevated by the injection of tryptophan or insulin, or by the consumption of carbohydrates, brain tryptophan and serotonin also rise; however, when even larger elevations of plasma tryptophan are produced by the ingestion of protein-containing diets, brain tryptophan and serotonin do not change. The main determinant of brain tryptophan and serotonin concentrations does not appear to be plasma tryptophan alone, but the ratio of this amino acid to other plasma neutral amino acids (that is, tyrosine, phenylalanine, leucine, isoleucine, and valine) that compete with it for uptake into the brain.     

Chelation of calcium by lactose: its role in transport mechanisms

Lactose, like other sugars and polyols, prevents or delays the precipitation of calcium ion in the presence of bicarbonate buffer. That an uncharged calcium-lactose complex is formed was demonstrated by the use of paper electrophoresis and of calcium-45 as a label for the complex. Enhancement of the intestinal absorption of calcium ion by sugars could result from a complex of low molecular weight.     

Crayfish muscle receptor organ: role in regulation of postural flexion

Recordings were made from postural-control motor nerves with antagonistic functions in the crayfish abdomen through flexible suction electrodes. During unrestrained flexion of the abdomen, output from the tonic stretch receptor neuron of RM(1),(SR(1)) is sufficient to drive an extensor motor unit in the same segment. However, this intrasegmental "resistance" reflex is normally blocked by an intersegmental reflex in which output from SR(1)'s in caudal segments inhibits SR(1) discharge in more anterior segments.     

Calmodulin plays a pivotal role in cellular regulation

The role of calcium ions (Ca2+) in cell function is beginning to be unraveled at the molecular level as a result of recent research on calcium-binding proteins and particularly on calmodulin. These proteins interact reversibly with Ca2+ to form a protein . Ca2+ complex, whose activity is regulated by the cellular flux of Ca2+. Many of the effects of Ca2+ appear to be exerted through calmodulin-regulated enzymes.     

Heat production and temperature regulation in eastern skunk cabbage

The spadix of Symplocarpus foetidus L. maintains an internal temperature 15 degrees to 35 degrees C above ambient air temperatures of -15 degrees to +15 degrees C. For at least 14 days it consumes oxygen at a rate comparable to that of homeothermic animals of equivalent size. Temperature regulation is accomplished by variations in respiratory rate.     

Thyroid gangliosides with high affinity for thyrotropin: potential role in thyroid regulation

Thyroid cell membranes contain a multiplicity of gangliosides, some of which inhibit thyrotropin binding to thyroid membranes. The most potent inhibitor is a ganglioside which is present in only trace amounts and appears to have a novel structure. Thyroid gangliosides may play a role in relaying the hormonal message to the thyroid cell.     

Fever: reciprocal shift in brain sodium to calcium ratio as the set-point temperature rises

A bacterial pyrogen acts on the brain by disturbing the natural balance between two essential cations in the cerebral region involved in thermoregulation. After typhoid vaccine is administered to the unanesthetized cat, (45)Ca(2+) efflux into the third cerebral ventricle increases while (22)Na(+) is retained in hypothalamic tissue at the same time that the set-point temperature begins to rise. The subsequent rates of (22)Na(+) and (45)Ca(2+) efflux parallel the course of the bacterial fever but in a reciprocal fashion. This supports the theory that a change in the set-point temperature is determined by an alteration in the inherent ratio of Na(+) to Ca(2+) ions in the hypothalamus.     

光信号和低温调控植物休眠研究进展

休眠是高等植物通过暂停生长发育而在不利条件下存活的策略,主要由遗传和环境因素控制,对植物生长发育具有重要意义。植物响应季节变化的2个主要环境信号是光周期和温度。本文采用文献综述法,追踪国内外最新相关研究结果进行分析。系统梳理了秋冬季光信号和低温在植物年生长周期的时间调节中起到的关键作用,阐明了植物种间和种内因基因表达、蛋白互作及转录后修饰等途径建立起的特异性休眠机制及休眠机制中存在的巨大差异。综述了植物休眠领域研究存在的主要问题并展望了未来研究重点,可为揭示秋冬光信号和低温条件下的植物休眠机制提供参考。     

Sea-surface temperature from coral skeletal strontium/calcium ratios

Seasonal records of tropical sea-surface temperature (SST) over the past 10(5) years can be recovered from high-precision measurements of coral strontium/calcium ratios with the use of thermal ionization mass spectrometry. The temperature dependence of these ratios was calibrated with corals collected at SST recording stations and by (18)O/(16)O thermometry. The results suggest that mean monthly SST may be determined with an apparent accuracy of better than 0.5 degrees C. Measurements on a fossil coral indicate that 10,200 years ago mean annual SSTs near Vanuatu in the southwestern Pacific Ocean were about 5 degrees C colder than today and that seasonal variations in SST were larger. These data suggest that tropical climate zones were compressed toward the equator during deglaciation.     

HPM设计绘图程序中板下温度的合理确定

根据热平衡的原理，探讨了不采暖房间温度的确定，使HPM绘图设计软件在应用中更加准确方便。     

温度在水产动物性别控制中的作用

就孵化温度(胚胎发育温度)和幼体发育温度对水生甲壳类、贝类、鱼类、两栖类和爬行类性别分化和性腺发育的影响作了简要介绍.总的趋势是高温有利于雄性化,而低温则有利于雌性化.另外,综述还对其作用机制作了初步探讨.     

温度在水产动物性别控制中的作用

就孵化温度(胚胎发育温度)和幼体发育温度对水生甲壳类、贝类、鱼类、两栖类和爬行类性别分化和性腺发育的影响作了简要介绍.总的趋势是高温有利于雄性化,而低温则有利于雌性化.另外,综述还对其作用机制作了初步探讨.     

A new role for temperature in insect dormancy: cold maintains diapause in temperate zone Diptera

In early autumn, high temperatures terminate diapause in the alfalfa blotch leafminer Agromyza frontella; low temperatures maintain diapause. These responses subserve a thermally malleable dormancy and allow flexibility in the annual number of generations. The view that favorable conditions cannot reverse the course of diapause are contradicted by the data on A. frontella. A better understanding to life history studies and phenological models in insect pest management.     

温度对植物开花时间调控的研究进展

开花是高等植物生长繁殖过程中重要的生理现象,是植物由营养生长进入生殖生长的标志。植物开花受多种内源和外源因素的调节,其中温度是影响植物开花的一个重要环境因素。总结了近期温度影响开花(主要包括春化途径和热感应途径)的研究进展,尤其对最近研究发现的FT及其家族基因和相关上游转录因子以及miRNA在植物响应温度变化影响开花过程中的功能进行了综述,有助于进一步了解温度参与植物开花调控的分子机制。     

Brain imaging: applications in psychiatry

Various brain imaging techniques have become available in the past decade. These include techniques to evaluate brain structure, such as computed tomography and magnetic resonance imaging, and techniques to assess functional activity, such as measurement of regional cerebral blood flow, single photon emission computed tomography, and positron emission tomography. These techniques can be used to map brain structure and function in normal human beings, and they have enlarged our knowledge of the pathophysiology of mental illnesses by demonstrating structural, metabolic, and neurochemical abnormalities in a wide range of mental disorders.     

Cell cycle regulation of myosin-V by calcium/calmodulin-dependent protein kinase II

Organelle transport by myosin-V is down-regulated during mitosis, presumably by myosin-V phosphorylation. We used mass spectrometry phosphopeptide mapping to show that the tail of myosin-V was phosphorylated in mitotic Xenopus egg extract on a single serine residue localized in the carboxyl-terminal organelle-binding domain. Phosphorylation resulted in the release of the motor from the organelle. The phosphorylation site matched the consensus sequence of calcium/calmodulin-dependent protein kinase II (CaMKII), and inhibitors of CaMKII prevented myosin-V release. The modulation of cargo binding by phosphorylation is likely to represent a general mechanism regulating organelle transport by myosin-V.