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41.
David J. Gower Jens B. Rasmussen Simon P. Loader Mark Wilkinson 《African Journal of Ecology》2004,42(2):83-87
A report is given of an adult caecilian, Scolecomorphus kirkii, found in the gut of a specimen of the snake Atractaspis aterrima from the Udzungwa Mountains, Tanzania. Both predator and prey are largely fossorial in soil, and their ecology is poorly known, such that this is the first reported predator of any scolecomorphid caecilian. The caecilian was ingested head first and much of the flesh from the anterior of the specimen had been digested. The prey/predator mass ratio is 0.48. This value is substantially higher than reported for A. aterrima from West Africa, and refutes the notion that this species feeds only on small prey. Most reported predators of caecilians are snakes, and a brief review is presented. 相似文献
42.
Jens M. Olesen Yoko L. Dupont Bodil K. Ehlers Alfredo Valido Dennis M. Hansen 《Nordic Journal of Botany》2003,23(5):537-539
Jasminum odoratissimum is a Madeira and Canary Islands endemic showing classic heterostyly, i.e. with long-styled flowers with anthers at a low level in the corolla tube and short-styled flowers with anthers at a high level in the corolla tube. Short-styled flowers have large pollen, whereas long-styled flowers have small pollen. The two types are present in equal frequencies in the population. 相似文献
43.
44.
Uptake of 24Mg by excised pine roots: A preliminary study 总被引:1,自引:0,他引:1
Uptake of 24Mg by excised roots of Pinus sylvestris L. during up to 4 h long incubations in 99.9 atom % 24Mg (50 M) was measured by ICP-MS. A rapid initial uptake phase (30 min) was followed by a slower uptake. This was interpreted as a shift from a phase dominated by saturable ion exchange (free space uptake), to a non-saturable phase, during which the rate of uptake was 0.077±0.0.012 mol Mg g–1 (d.wt.) h–1. The metabolic uncoupler DNP (2,4-dinitrophenol) at 50 M decreased the Mg uptake rate by 35% only, but the effect of DNP was significant (p<0.01). Several problems related to a high variability in the experimental material were encountered, and further refinement of this approach in studies of plant Mg uptake is suggested. 相似文献
45.
Mikkel Nissum Jens-Jakob Karlsson Jens Ulstrup Palle Waage Jensen G. Smulevich 《Journal of biological inorganic chemistry》1997,2(3):302-307
Di-heme Pseudomonas stutzeri cytochrome c
4 has been characterized by electronic absorption and resonance Raman spectroscopies in the ferric and ferrous forms at pH 7.5
and at room temperature. The data indicate that the two hemes are inequivalent. It is proposed that the N-terminal contains
a more relaxed heme as a consequence of the relative orientation of the methionine and histidine ligands with respect to the
N-Fe-N directions of the heme plane. This causes a weakening of the Fe-S bond with concomitant partial dissociation of the
methionine and the formation of an Fe-aquo bond. Heme group relaxation is further accompanied by less distortion of the heme
group than that associated with cytochrome c, expansion of the "core" and a negative shift of the redox potential.
Received: 17 December 1996 / Accepted: 6 March 1997 相似文献
46.
Wolf-Dietrich Hard Jens M. Warnecke Roland K. Hartmann 《Molecular biology reports》1995,22(2-3):161-169
Modification interference is a powerful method to identify important functional groups in RNA molecules. We review here recent developments of techniques to screen for chemical modifications that interfere with (i) binding of(pre-)tRNA to bacterial RNase P RNA or (ii) pre-tRNA cleavage by this ribozyme. For example, two studies have analyzed positions at which a substitution of sulfur for thepro-Rp oxygen affects tRNA binding [1] or catalysis [2]. The results emphasize the functional key role of a central core element present in all known RNase P RNA subunits. The four sulfur substitutions identified in one study [2] to inhibit the catalytic step also interfered with binding of tRNA toE. coli RNase P RNA [1]. This suggests that losses in binding energy due to the modification at these positions affect the enzyme-substrate and the enzyme-transition state complex. In addition, the two studies have revealed, for the first time, sites of direct metal ion coordination in RNase P RNA. The potentials, limitations and interpretational ambiguities of modification interference experiments as well as factors influencing their outcome are discussed.Abbreviations nt
nucleotide(s)
- PAGE
polyacrylamide gel electrophoresis 相似文献
47.
Jens Meyer Norbert Elsner 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,176(4):563-573
1. | Up to 9 kHz, the tympanal membrane of the grasshopper Chorthippus biguttulus responds with equal sensitivity at the attachment sites of the low and the high-frequency receptors; at the latter site it is also particularly sensitive between 10 and 20 kHz. |
2. | The frequency spectra of the songs of both sexes exhibit maxima at 7–8 kHz, to which the membrane is well matched. In the high-frequency region, where the male songs have a peak at 30 kHz, there is no corresponding maximum in the membrane oscillation. |
3. | Because the tympanal membrane is immediately adjacent to air sacs in the tracheal system, it is deflected inward and outward by as much as 80 m during the respiratory cycle. |
4. | Measurements by laser vibrometry show that acoustically induced membrane oscillations are attenuated severely due to the respiratory displacement of the membrane for frequencies up to 10–12 kHz. By contrast, at higher frequencies the membrane sensitivity is doubled or tripled. |
5. | As a result of these membrane effects, the discharge in the tympanal nerve was profoundly reduced in the low-frequency range, whereas above 11 kHz there was a marked increase. This modulation of auditory sensitivity affects the animals' ability to detect conspecific songs. |
48.
Sulphur-heterotrophic growth exhibited a dual response to the expression of sulphate-assimilating enzymes. The level of ATP-sulphurylase (EC 2.7.7.4) appeared repressed while sulphite reductase (EC 1.8.7.1) and O-acetyl-l-serine sulphhydrylase (EC 4.2.99.8) were derepressed and coordinated in their occurrence. The capability of the cells to reduce adenylylphosphosulphate or 3-phospho adenylylphosphosulphate to cysteine coincided with the activity of sulphite reductase. The expression of these reducing steps lacked correlation with the regulation of ATP-sulphurylase.Abbreviations APS
adenylylphosphosulphate
- MVH
reduced methylviologen
- OAS
O-acetyl-l-serine
- PAPS
3-phospho adenylylphosulphate 相似文献
49.
An improved timm sulphide silver method for light and electron microscopic localization of heavy metals in biological tissues 总被引:3,自引:0,他引:3
Summary Modifications of the Timm sulphide silver method for the demonstration of heavy metals are described.To improve the structural preservation of the tissues perfusion with a glutaraldehyde fixative is employed before perfusion with the sodium sulphide solution. For the subsequent staining for light and electron microscopy, procedures for plastic embedding, paraffin embedding and cryostat sectioning are presented. Examples from several tissues are shown, including the pituitary, pancreas, intestine, tongue, kidney, testis and brain. The staining of autolytic, postmortal human brain tissue is demonstrated. 相似文献
50.