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611.
Cationic polypeptide-induced fusion of acidic liposomes 总被引:1,自引:0,他引:1
Alexander E. Gad 《生物化学与生物物理学报:生物膜》1983,728(3):377-382
Fusion of acidic liposomes was induced by Mg2+, Ca2+, polylysine and polymyxin B. The extent of fusion and the concomitant change in liposome permeability induced by divalent cations depended on the concentration of liposomes in the suspension as well as on the cation concentration. In contradistinction, the extent of fusion and the change in permeability induced by the polypeptides depended only on the polycation concentration. The difference in the pattern of interaction, between the liposomes and the various cations, is a result of different binding affinities. The binding of the polypeptides to the liposomes, in contrast to divalent cations, is practically irreversible. The potential of polylysine to induce fusion of acidic phosphatidylethanolamine-devoid liposomes was used to demonstrate that in order to obtain fusion, both membranes involved must be susceptible, at least to a certain degree, to fusion by the proper inducer. When lysophosphatidylcholine substituted for phosphatidylcholine in phosphatidylethanolamine-rich acidic liposomes, extensive polylysine-induced fusion was obtained without concomitant spillage of the liposome contents. 相似文献
612.
Michael E. Foley 《Physiologia plantarum》1986,67(4):690-694
Fusicoccin induced germination in dormant and partially afterripened dormant caryopses of Avena fatua L. The rate of caryopsis germination was slower and final percentage germination lower in the highly dormant inbred line M73 at a given concentration of fusicoccin than in the dormant caryopses of line AN265. Gibberellic acid was more effective than fusicoccin in breaking dormancy in both lines. Promotion of germination of dormant caryopses by fusicoccin was inhibited by a 6-day pretreatment with (2-chloroethyl)trimethylammonium chloride.
The basal rate of proton efflux from embryos isolated from dormant and fully afterripened line AN265 caryopses was similar. Addition of fusicoccin increased the rate of proton efflux from the isolated embryos of dormant and afterripened caryopses by nearly 400%. Gibberellic acid had no effect on the rate of proton extrusion. The uptake of86 Rb+ in dormant and afterripened A. fatua embryos was similar after a 2 h uptake period. The addition of fusicoccin to the medium doubled the uptake of 86 Rb4 by dormant and afterripened embryos. Gibberelleic acid had no effect on the uptake of 86 Rb+ by isolated embryos from either dormant or afterripened caryopses. The experimental results indicate that gibberellic acid is more versatile in its action than fusicoccin, and gibberellic acid may facilitate dormant A. fatua caryopsis germination by stimulating mechanisms other than the direct H+ efflux and K+ uptake at the membrane level. 相似文献
The basal rate of proton efflux from embryos isolated from dormant and fully afterripened line AN265 caryopses was similar. Addition of fusicoccin increased the rate of proton efflux from the isolated embryos of dormant and afterripened caryopses by nearly 400%. Gibberellic acid had no effect on the rate of proton extrusion. The uptake of
613.
Ou CN 《Journal of biomedical science》1997,4(6):315-318
This report describes a unique cation exchange high-performance liquidchromatography capable of separating more than 40 frequently encountered human hemoglobins and variants within 12 min. Some of these variants are unresolvable by the conventional electrophoretic methods and would thus lead to an incorrect diagnosis of hemoglobinpathy. The method provides high sensitivity, superior resolution and accurate quantitation of hemoglobin concentrations. It can also be fully automated thus make it an ideal methodology for the diagnosis of hemoglobin disorders in a routine clinical laboratory. 相似文献
614.
The existence of an endogenous protein kinase activity and protein phosphatase activity in myelin membrane from mammalian brain has now been well established. We found that under all conditions tested the myelin basic protein is almost the only substrate of the endogenous protein kinase in myelin of bovine brain. The protein kinase activity is stimulated by Ca2+ in the micromolar range. Optimal activity is reached at a free Ca2+ concentration of about 2 μM. Myelin membrane vesicles were prepared and then shown to be sealed by a light-scattering technique. After preloading with 45Ca2+, 86Rb+, or 22Na+, the self-diffusion (passive outflux) of these ions from myelin membrane vesicles was measured. Ionophores induced a rapid, concentration-dependent outflux of 80–90% of the cations, indicating that only a small fraction of the trapped ions was membrane bound. There was no difference in the diffusion rates of the three cations whether phosphorylated (about 1 mol phosphate per myelin basic protein) or non-phosphorylated vesicles were tested. In contrast, a small but significant decrease in permeability for Rb+ and Na+ was measured, when the vesicles were pretreated with ATP and Mg2+. 相似文献
615.
Tree Patches Show Greater N Losses but Maintain Higher Soil N Availability than Grassland Patches in a Frequently Burned Oak Savanna 总被引:3,自引:0,他引:3
Long-term prescribed fires have increased woody canopy openness and reduced nitrogen (N) cycling (that is, net N mineralization)
in an oak savanna in Minnesota, USA. It is unclear how fire-induced shifts from oak-dominated to C4 grass-dominated vegetation
contribute to this decline in N cycling compared to direct effects of increasing fire frequency promoting greater N losses.
We determined (1) the magnitude of decline in net N mineralization in oak versus grass-dominated patches with increasing fire
frequency and (2) if differences in net N mineralization between oak and grass patches in frequently burned oak savanna (burned
8 out of 10 years on average during the last 40 years) could be attributed to differences in N losses through volatilization
and leaching or to plant traits affecting decomposition and mineralization. In situ net N mineralization declined with increasing fire frequency overall, but this decline was less in oak- than in grass-dominated
patches, with oak-dominated patches having more than two times higher net N mineralization than grass-dominated patches. Greater
net N mineralization in oak-dominated patches occurred despite greater N losses through volatilization and leaching (on average
1.8 and 1.4 g m−2 y−1 for oak- and grass-dominated patches, respectively), likely because of higher plant litter N concentration in the oak-dominated
patches. As total soil N pools in the first 15 cm did not differ between oak- and grass-dominated patches (on average 83 g
N m−2), N inputs from atmospheric deposition and uptake from deep soil layers may offset higher N losses. Our results further show
that net N mineralization rates decline within 5 years after tree death and subsequent colonization by C4 grasses to levels
observed in grass-dominated patches. Although long-term prescribed fires often directly reduce N stocks and cycling because
of increased N losses, this study has shown that fire-induced shifts in vegetation composition can strongly contribute to
the declines in N cycling in systems that are frequently disturbed by fires with potential feedbacks to plant productivity. 相似文献
616.
Filip Oulehle William H. McDowell Jacqueline A. Aitkenhead-Peterson Pavel Krám Jakub Hruška Tomáš Navrátil František Buzek Daniela Fottová 《Ecosystems》2008,11(3):410-425
Stream nitrogen (N) export and nitrate concentration were measured at 14 forested watersheds (GEOMON network) in the Czech Republic between 1994 and 2005. In the
last several decades, emissions of sulfur (S) and N compounds have decreased throughout much of Europe. In the Czech Republic,
atmospheric deposition of S has decreased substantially since the beginning of 1990s, whereas N deposition remains largely
unchanged at most sites. The mean dissolved inorganic nitrogen (DIN) streamwater export ranged from 0.2 to 12.2 kg ha−1 y−1 at the GEOMON sites. Despite decades of elevated N deposition, 44–98% of DIN inputs to these watersheds were retained or
denitrified, and many watersheds showed seasonal variation in nitrate concentrations. Dissolved organic N export was quantified
in 1 year only and ranged from 0.05 to 3.5 kg ha−1 y−1. Spatial variability in DIN export among watersheds was best explained by spatial variability in average acidic deposition,
particularly S deposition (R
2 = 0.81, P < 0.001); DIN input and forest floor carbon:nitrogen (C/N) also provided significant explanatory power. DIN export was strongly
influenced by the forest floor C/N ratio and depth of the forest floor soils (R
2 = 0.72, P < 0.001). The only variable that predicted variations in forest floor C/N (R
2 = 0.32, P < 0.05) among watersheds was S deposition. Forest floor depth was also related to deposition variables, with S deposition
providing the most explanatory power (R
2 = 0.50, P < 0.01). Variation in forest floor depth was also associated with climatic factors (precipitation and temperature). Temporal
variability in DIN export was primarily associated with changes in acidic deposition over time; S deposition explained 41%
of variability in DIN exports among all watersheds and years. Extensive acidification of forested watersheds was associated
with the extraordinarily high S inputs to much of the Czech Republic during earlier decades. We hypothesize that recovery
from acidification has led to improved tree health as well as enhanced microbial activity in the forest floor. As these watersheds
move into a new regime with dramatically lower sulfur inputs, we expect continued declines in nitrate output. 相似文献
617.
618.
Montell C 《Cell calcium》2003,33(5-6):409-417
The transient receptor potential (TRP) superfamily is subdivided into four main classes of cation channels, TRPC, TRPV, TRPM and TRPN, each of which includes members in worms, flies, mice and humans. While the biophysical features of many of the mammalian channels have been described, relatively little is known concerning the biological roles of these channels. Forward genetic screens in Drosophila melanogaster and Caenorhabditis elegans have led to the identification of the founding members of each of these four subfamilies. Moreover, phenotypic analyses of invertebrate mutants have contributed greatly to our understanding of the roles of TRP proteins. A recurring theme is that many of these proteins function in sensory signaling processes ranging from vision to olfaction, osmosensation, light touch, social feeding, and temperature- and mechanically-induced nociception. In addition, at least one invertebrate TRP protein is required for cell division. As many of these functions may be conserved among the mammalian TRPs, the invertebrate TRPs offer valuable genetic handles for characterizing the functions of these cation channels in vivo. 相似文献
619.
Jackson PL Cao L Blalock JE Whitaker JN 《Archives of biochemistry and biophysics》2003,418(2):119-124
Urinary myelin basic protein-like material (MBPLM), so designated because of its immunoreactivity with a polyclonal antibody directed against a cryptic epitope located in residues 83-89 of myelin basic protein (MBP), exists in humans normally but increases in concentration in patients with multiple sclerosis who have progressive disease. Given its possible role in reflecting events of neural tissue destruction occurring in multiple sclerosis, urinary MBPLM is a candidate surrogate marker for this phase of the disease. Previously, it has been demonstrated that p-cresol sulfate (PCS) is the dominant component of MBPLM; however, another component(s) was essential in enabling p-cresol sulfate to have molecular mimicry with MBP peptide 83-89 detected by immunoreactivity. In the present investigation, this remaining component(s) was characterized by a combination of high performance size exclusion chromatography followed by nuclear magnetic resonance spectroscopy and shown to be ammonium. The monovalent cation ammonium could be substituted in vitro by several different monovalent and divalent cations, most notably zinc, in restoring to deprotonated p-cresol sulfate its immunoreactivity as MBPLM. These findings indicate the basis for the unexpected molecular mimicry between an epitope of an encephalitogenic protein and a complex containing a small organic molecule, p-cresol sulfate. Furthermore, the reaction of either ammonium or other cations with p-cresol sulfate may represent an in vivo process directly related to damage of axonal membranes. 相似文献
620.
Sokolova O 《FEBS letters》2004,564(3):251-256
A large barrier in the way to obtaining high-resolution structures of eukaryotic ion channels remains the expression and purification of sufficient amounts of channel protein to carry out crystallization trials. In the absence of crystals, the main available source of structural information has been electron microscopy (EM), which is well suited to the visualization of isolated macromolecular complexes and their conformational changes. The recently published EM structures outline native conformations of eukaryotic cation channels that until now have eluded crystallization. According to these results, homo-tetrameric K(+) channels have a distinct two-layer architecture with connectors conjoining the two layers, while the pseudo-tetrameric Ca(2+) or Na(+) channels are more globular and have flexible surface loops, which makes the identification of subunits complicated. Subunits can be identified using atomic structure docking into the EM maps, labeling, or deletion studies. 相似文献