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861.
Most mammals, with the exception of primates, have dichromatic vision and correspondingly limited colour perception. Ultraviolet vision was discovered in mammals only a decade ago, and in the few rodents and marsupials where it has been found, ultraviolet light is detected by an independent photoreceptor. Bats orient primarily by echolocation, but they also use vision. Here we show that a phyllostomid flower bat, Glossophaga soricina, is colour-blind but sensitive to ultraviolet light down to a wavelength of 310 nm. Behavioural experiments revealed a spectral-sensitivity function with maxima at 510 nm (green) and above 365 nm (ultraviolet). A test for colour vision was negative. Chromatic adaptation had the same threshold-elevating effects on ultraviolet and visible test lights, indicating that the same photoreceptor is responsible for both response peaks (ultraviolet and green). Thus, excitation of the beta-band of the visual pigment is the most likely cause of ultraviolet sensitivity. This is a mechanism for ultraviolet vision that has not previously been demonstrated in intact mammalian visual systems. 相似文献
862.
Jones JM Datta P Srinivasula SM Ji W Gupta S Zhang Z Davies E Hajnóczky G Saunders TL Van Keuren ML Fernandes-Alnemri T Meisler MH Alnemri ES 《Nature》2003,425(6959):721-727
The mouse mutant mnd2 (motor neuron degeneration 2) exhibits muscle wasting, neurodegeneration, involution of the spleen and thymus, and death by 40 days of age. Degeneration of striatal neurons, with astrogliosis and microglia activation, begins at around 3 weeks of age, and other neurons are affected at later stages. Here we have identified the mnd2 mutation as the missense mutation Ser276Cys in the protease domain of the nuclear-encoded mitochondrial serine protease Omi (also known as HtrA2 or Prss25). Protease activity of Omi is greatly reduced in tissues of mnd2 mice but is restored in mice rescued by a bacterial artificial chromosome transgene containing the wild-type Omi gene. Deletion of the PDZ domain partially restores protease activity to the inactive recombinant Omi protein carrying the Ser276Cys mutation, suggesting that the mutation impairs substrate access or binding to the active site pocket. Loss of Omi protease activity increases the susceptibility of mitochondria to induction of the permeability transition, and increases the sensitivity of mouse embryonic fibroblasts to stress-induced cell death. The neurodegeneration and juvenile lethality in mnd2 mice result from this defect in mitochondrial Omi protease. 相似文献
863.
The chirality of l-/dl-leucine (50–50%) cooligomerization was investigated in liquid and frozen aqueous solutions. Cooligomerization was carried
out by carbonyldiimidazole activation without initiator at an ambient (+22°C) and frozen (−18°C) temperature, respectively.
The separated samples obtained after different time intervals of treatment were completely hydrolyzed (HCl) and the diastereomeric
l- and d-leucine derivates of Marfey's reagent (1-fluoro-2,4-dinitrophenyl-5-l-alanine amide) were then traced and evaluated by RP-HPLC analysis. After 9 days of oligomerization, the l-Leu content was slightly enhanced in the liquid (57%) and somewhat more enhanced in the frozen (64%) samples. After 17 days,
however, the l-Leu content had decreased in the liquid (53%) and frozen (56%) conditions. These l-enantiomer amplifications indicate that an l-antipode is preferentially incorporated into the α-helical turn of the oligomer in the earlier stage of cooligomerization, while, later, the d-antipode is also incorporated. The role of ice in the improved stereoselection is discussed. This is the first recorded example
of the effect of freezing on stereoselection.
Received 27 October 2000; revised 11 December 2000; accepted 4 January 2000 相似文献
864.
Hernán López-Garay 《Systemic Practice and Action Research》1991,4(5):491-505
This interpretive systemic study is part of a major research project whose primary goal is to unfold the holistic meaning of Regional Planning Corporations in Venezuelan society. Using the methodological guidelines of Interpretive Systemology, the Regional Planning Corporation of Los Andes is studied as a system-whole (as opposed to a set of interrelated parts and functions). Accordingly, different interpretive contexts are built, and an attempt is made to interpret with them the actuality of the Corporation. However, the attempt is not successful because its actual organizational activities cannot be fully accounted for in these contexts. Hence the need to search for more powerful interpretations arises. In so doing, the holistic character of the organization is displayed in its multiple and contrasting interpretations. 相似文献
865.
866.
Résumé L'ATP induit la libération de catécholamines des granules chromaffines médullaires. Nous discutons le rôle du Cl– dans ce processus vis-à-vis l'activité de l'ATPase et la phosphorylation des membranes. Nos résultats indiquent que la réaction aboutissant à la liberation de catécholamines est un phenomène comportant plusieurs étapes échelonnées après l'hydrolyse de l'ATP.
Supported by the Medical Research Council of Canada. 相似文献
Supported by the Medical Research Council of Canada. 相似文献
867.
868.
869.
Zusammenfassung Auf Grund der Laktonregel vonHudson konnte dem (—) 3·6-Dihydroxy-tropan und (—) Valeroidin eine absolute Konfiguration zugeschrieben werden. 相似文献