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21.
A series of the protected alkyl glycosides 5a/5b-12a/12b was synthesized from the parent isomeric alcohols (insect juvenile hormone bioanalogs; juvenoids), 4-[4'-(2'-hydroxycyclohexyl)methylphenoxy]-3-methyl-but-2-enoic acid ethyl ester (1a/1b-4a/4b; racemic structures) and (1a-4a; enantiopure structures). Cadmium carbonate was used as a promoter of this Koenigs-Knorr reaction, and the products were obtained in 82-92% yields. Deprotection of the carbohydrate functionality of 5a/5b-12a/12b was carefully performed using ethanolysis in the presence of zinc acetate, due to the presence of another ester functionality in the aglycone part of the molecule of protected alkyl glycosides. Resulting alkyl glycosides 13a/13b-20a/20b (diastereoisomeric mixtures) and 13a-20a (enantiopure compounds), biochemically activated hormonogenic compounds (juvenogens), were obtained in 82-93% yields. Finally, chiral HPLC separation of the diastereoisomeric mixtures of alkyl glycosides was applied to get sufficient quantities of the respective enantiomers 13b-20b of the alkyl glycosides for their structure elucidation and (13)C chemical shift assignment by (1)H and (13)C NMR spectroscopy. Partial introductory entomological screening tests of the target alkyl glycosides 13a/13b-20a/20b were performed on the red firebug (Pyrrhocoris apterus). The results of this biological testing clearly demonstrated the time-extended effect of several juvenogens on P. apterus due to their biochemical activation, i.e., hydrolysis of the juvenogen molecule, which results in liberation of the biologically active juvenoid in the insect organism.  相似文献   
22.
Dietary betaine may reduce carcass fat in growing pigs. We explored the effects of betaine on short-term growth and in vivo and in vitro fatty acid oxidation. Pigs were housed in metabolism crates and fed diets containing either 0% (control), 0.125% or 0.5% betaine at 80% of ad libitum energy intake. Fatty acid oxidation was measured during intravenous infusions of 1-(13)C-palmitate and in hepatocytes incubated in the presence or absence of betaine and carnitine. CO2 and palmitate isotopic enrichments were determined by mass spectrometry. Pigs consuming 0.125% and 0.5% betaine for at least 9 days had growth rates that were 38% and 12% greater than controls, respectively. Feed efficiency was also improved with betaine. Fasting increased palmitate oxidation rates 7-8-fold (P < 0.01), but betaine had no effect in either the fed or fasted state (P > 0.1). For hepatocytes, carnitine but not betaine enhanced palmitate oxidation. This response suggests that previously observed reduction in adipose accretion must be via a mechanism other than oxidation. Betaine had no effect on plasma non-esterified fatty acids or urea nitrogen. Under the confinement conditions in this study, dietary betaine improved animal growth responses, but it had no apparent effect on either whole body or hepatic fatty acid oxidation.  相似文献   
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Hatching asynchrony is the consequence of birds initiating incubation before clutch completion. It has been suggested that variation in hatching asynchrony in owls is extensive, and therefore they should be excellent objects to study the effects of spatio-temporal variation in food abundance on this phenomenon. We examined how abundance and predictability of food affected hatching asynchrony in Tengmalm's owl Aegolius funereus (Linnaeus), which mainly feeds on voles which fluctuate in 3- to 4-year cycles in northern Europe. Hatching span averaged 6-7 days (range 0-13 days) and increased with clutch size. Food supply did not directly influence levels of hatching asynchrony but it influenced indirectly via marked among-year changes in clutch size. During the decrease phase of the vole cycle the proportion of hatchlings producing fledglings decreased with asynchrony, suggesting that chick mortality was most common among asynchronous broods when food became scarce. This finding is consistent with Lack's brood reduction hypothesis, i.e. that if food becomes scarce during the nestling period the youngest nestlings would die first without endangering the survival of the whole brood.  相似文献   
25.
Real time observation of reaction kinetics is one of the key features of the newly developed microparticle based two-photon excitation fluorescence immunoassay system (TPX). By observing binding reactions at the surface of individual microparticles during the incubation of an assay, the binding constants of an assay become apparent. This paper describes the use of the new system in quantifying the reaction parameters of human thyroid stimulating hormone (hTSH) assay. A mechanistic reaction model for the assay is presented. The reaction model is further shown to precisely predict the behaviour of the assay kinetics over a wide range of analyte concentrations.  相似文献   
26.
Peptidyl-tRNA hydrolase (Pth) activity releases tRNA from the premature translation termination product peptidyl-tRNA. Two different enzymes have been reported to encode such activity, Pth present in bacteria and eukaryotes and Pth2 present in archaea and eukaryotes. Here we report the crystallographic structure of the Homo sapiens Pth2 at a 2.0-A resolution as well as its catalytic properties. In contrast to the structure of Escherichia coli Pth, H. sapiens Pth2 has an alpha/beta fold with a four-stranded antiparallel beta-sheet in its core surrounded by two alpha-helices on each side. This arrangement of secondary structure elements generates a fold not previously reported. Its catalytic efficiency is comparable with that reported for the archaeal Sulfolobus solfataricus Pth2 and higher than that of the bacterial E. coli Pth. Several lines of evidence target the active site to two close loops with highly conserved residues. This active site architecture is unrelated to that of E. coli Pth. In addition, intermolecular contacts in the crystal asymmetric unit cell suggest a likely surface for protein-protein interactions related to the Pth2-mediated apoptosis.  相似文献   
27.
The Archipelago Sea in the northern Baltic has been subjected to large-scale cultural, economic and ecological changes, especially during the last three decades. Environmental threats originate from both basin-wide sources, affecting the whole Baltic Sea, and from local sources, such as nutrient loading from nearby river outflows, intense agriculture, fish farming, ships' traffic, boating, and man's physical impacts on the landscape and seascape. Both the Åland archipelago and the Archipelago Sea have been listed as hot-spots by HELCOM, Baltic Marine Environment Protection Commission, eutrophication being the main threat to the aquatic environment. In this study we review how biological communities have reacted to an increase in man-induced multisource stresses. Changes in plankton, benthic animals, macroalgal assemblages and fish communities have been documented in most parts of the Baltic Sea since the 1970s. What remains to be understood is the importance of these structural changes for the functioning of the Archipelago Sea ecosystem under various levels of human impact.  相似文献   
28.
Masoero  Giulia  Laaksonen  Toni  Morosinotto  Chiara  Korpim&#;ki  Erkki 《Oecologia》2020,192(3):699-711
Oecologia - Fluctuations in the abundance of main prey species might shape animal communities, by inducing numerical responses and dietary shifts in predators. Whether numerical responses and...  相似文献   
29.
Huitu O  Norrdahl K  Korpimäki E 《Oecologia》2003,135(2):209-220
Populations of northern small rodents have previously been observed to fluctuate in spatial synchrony over distances ranging from tens to hundreds of kilometers between sites. It has been suggested that this phenomenon is caused by common environmental perturbations, mobile predators or dispersal movements. However, very little focus has been given to how the physical properties of the geographic area over which synchrony occurs, such as landscape composition and climate, affect spatial population dynamics. This study reports on the spatial and temporal properties of vole population fluctuations in two areas of western Finland: one composed of large interconnected areas of agricultural farmland interspersed by forests and the other highly dominated by forest areas, containing more isolated patches of agricultural land. Furthermore, the more agricultural area exhibits somewhat milder winters with less snow than the forested area. We found the amplitude of vole cycles to be essentially the same in the two areas, suggesting that the relative amount of predation on small rodents by generalist versus specialist predators is similar in both areas. No seasonal differences in the timing of synchronization were observable for Microtus voles, whereas bank vole populations in field habitats appeared to become synchronized primarily during winter. Microtus populations in field habitats exhibited smaller spatial variation and a higher degree of synchrony in the more continuous agricultural landscape than in the forest-dominated landscape. We suggest that this inter-areal difference is due to differences in the degree of inter-patch connectivity, with predators and dispersal acting as the primary synchronizing agents. Bank vole populations in field habitats were more synchronized within the forest-dominated landscape, most likely reflecting the suitability of the inter-patch matrix and the possibility of dispersal. Our study clearly indicates that landscape composition needs to be taken into account when describing the spatial properties of small rodent population dynamics.  相似文献   
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