Active transport of Ca2+ by an artificial photosynthetic membrane

Transport of calcium ions across membranes and against a thermodynamic gradient is essential to many biological processes, including muscle contraction, the citric acid cycle, glycogen metabolism, release of neurotransmitters, vision, biological signal transduction and immune response. Synthetic systems that transport metal ions across lipid or liquid membranes are well known, and in some cases light has been used to facilitate transport. Typically, a carrier molecule located in a symmetric membrane binds the ion from aqueous solution on one side and releases it on the other. The thermodynamic driving force is provided by an ion concentration difference between the two aqueous solutions, coupling to such a gradient in an auxiliary species, or photomodulation of the carrier by an asymmetric photon flux. Here we report a different approach, in which active transport is driven not by concentration gradients, but by light-induced electron transfer in a photoactive molecule that is asymmetrically disposed across a lipid bilayer. The system comprises a synthetic, light-driven transmembrane Ca2+ pump based on a redox-sensitive, lipophilic Ca2+-binding shuttle molecule whose function is powered by an intramembrane artificial photosynthetic reaction centre. The resulting structure transports calcium ions across the bilayer of a liposome to develop both a calcium ion concentration gradient and a membrane potential, expanding Mitchell's concept of a redox loop mechanism for protons to include divalent cations. Although the quantum yield is relatively low (approximately 1 per cent), the Ca2+ electrochemical potential developed is significant.     

超临界CO_2脱卵黄油及卵黄磷脂提取的研究

对超临界CO_2流体萃取卵黄磷脂及其机制进行了研究,超临界CO_2在丙酮和瓷粉作用下,在35MPa、40℃条件下萃取3h,可脱除蛋黄粉中98.6％的卵黄油。在40MPa、50℃条件下,用10wt％乙醇夹带,卵黄中磷脂的提取率最高,为27.28％。     

Biosynthesis of animal and plant bufadienolides. Parallel experiments with pregn-5-en-3-ß-ol-20-one-20-14C inScilla maritima andBufo paracnemis

Zusammenfassung Pregnenolon-20-¹⁴C wird von roten Meerzwiebeln als Vorstufe für herzwirksame Glykoside verwendet, dagegen kannBufo paracnemis diese Produkte, subkutan appliziert, nicht in die üblichen Krötengifte überführen.     

Regional climate shifts caused by gradual global cooling in the Pliocene epoch

The Earth's climate has undergone a global transition over the past four million years, from warm conditions with global surface temperatures about 3 degrees C warmer than today, smaller ice sheets and higher sea levels to the current cooler conditions. Tectonic changes and their influence on ocean heat transport have been suggested as forcing factors for that transition, including the onset of significant Northern Hemisphere glaciation approximately 2.75 million years ago, but the ultimate causes for the climatic changes are still under debate. Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago. Our results suggest that mean low-latitude climate conditions can significantly influence global climate feedbacks.     

Rabbit abundance relative to rainfall and plant production in northern Chihuahuan Desert grassland and shrubland habitats

Rabbit abundance patterns in the North American Southwest are poorly known, particularly relative to the potentially important influences of rainfall and plant production. We conducted a 10-year study on the comparative densities of black-tailed jackrabbits ( Lepus californicus ) and desert cottontail rabbits ( Sylvilagus audubonii ) in relation to annual rainfall and plant production in both black grama ( Bouteloua eriopoda ) grassland and creosotebush ( Larrea tridentata ) shrubland habitats in the northern Chihuahuan Desert. We found that both species of rabbits were more abundant in black grama grassland than in creosotebush shrubland and that plant production was positively correlated with rainfall at both habitats. However, rabbit densities were not positively correlated with rainfall or plant production in either habitat. In fact, both species of rabbits exhibited gradual, multiyear changes in abundance rather than the patterns of high annual variation observed in desert rodent communities. Our findings of no significant relationship between plant production and rabbit densities indicate that rabbit abundance in the northern Chihuahuan Desert may not be strongly regulated by short-term, bottom-up effects of annual variation in plant production. Long-term trends indicate that other factors such as disease or predation may be equally or more important. We suggest that future research evaluate both top-down and bottom-up influences to elucidate the temporal dynamics of Chihuahuan Desert rabbit abundance. Se conoce poco sobre los patrones de abundancia de conejos desérticos en el suroeste de Norte America, particularmente en relación con las influencias potencialmente importantes de la precipitación y la producción de plantas. Llevamos a cabo una investigación de diez años sobre la densidad relativa de la liebre de California ( Lepus californicus ) y el conejo cola de algodón ( Sylvilagus audubonii ) en los hábitats tanto de pradera de grama negra ( Bouteloua eriopoda ) como de matorral de gobernadora ( Larrea tridentata ) en el norte del Desierto Chihuahuense, en relación con la precipitación y la producción anuales. Encontramos que ambas especies de conejo fueron más abundantes en la pradera de grama negra que en el matorral de gobernadora, y que la producción de plantas estuvo correlacionada positivamente con la precipitación en ambos hábitats. Sin embargo, las densidades de conejos no estuvieron correlacionadas positivamente con la precipitación o con la producción de plantas en ninguno de los dos hábitats. De hecho, en cuanto a la fluctuación de su abundancia, las dos especies de conejo exhibieron tendencias graduales a lo largo de varios años, en comparación con los patrones de gran variación anual que se han observado en comunidades de roedores desérticos. La falta de una relación significativa entre la producción de plantas y la abundancia de conejos, indica que la abundancia de conejos en el norte del Desierto Chihuahuense no está fuertemente regulada por los efectos ascendentes a corto plazo de la variación anual en la producción de plantas. Los cambios reflejados en las tendencias a largo plazo indican que otros factores como las enfermedades o la depredación pueden ser de igual o mayor importancia, y sugerimos que investigaciones futuras deberán evaluar tanto las influencias ascendentes como las descendentes para entender las dinámicas temporales en la abundancia de conejos del Desierto Chihuahuense.     

Effects of insulin hypoglycaemia on the adrenal medulla of the hamster

Résumé Pendant l'hypoglycémie insulinique (4 U/100 g), le hamster maintenu a 19°C présente une augmentation de l'adrénaline et de la noradrénaline plasmatiques, ainsi qu'une réduction de ces deux catécholamines dans les surrénales. Maintenu à 26°C, l'hypoglycémie se produit aussi bien avec 4 U/100 g d'insuline mais il n'y a pas de changements de l'adrénaline et noradrénaline du plasma et des surrénales. Pour obtenir des modifications, il est nécessaire d'augmenter la dose d'insuline à 8 U/100 g. En conclusion, la température extérieure a une influence marquée sur la réponse médullo-surrénale de l'hypoglycémie insulinique.     

Hypophysial feed-back in the hypothalamic regulation of luteinizing hormone secretion

Resumen LH exógeno disminuye LHRF circulante no así estradiol ni estradiol-progesterona, concluyéndose que: eminencia media regula LH siendo su nivel plasmático la señal feed-back.