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61.
Ion channels are found in most plant membranes. They catalyse the rapid passive uniport of particular ions with varying selectivity. Planar lipid-bilayer (PLB) techniques have been developed to study the electrical activities of single ion channels in well-defined lipid and aqueous environments. They greatly facilitate both the biophysical and biochemical characterisation of ion channels and complement both conventional impaling electrode and membrane-patch voltage-clamping (patch-clamping) electrophysiological techniques applied in vivo. Bilayers can be formed across the end of patch-clamp pipettes or across apertures in specifically designed chambers. Ion channels in native membranes and purified, genetically altered or synthetic ion channels, proteins and peptides can all be studied in PLBs. The main applications of PLBs are (1) to study ion channels in membranes inaccessible to patch-clamp electrodes, (2) to provide a functional assay system during channel-protein purification and (3) to investigate the relationship between the molecular structure of ion channels and their conductance properties. In the present article we describe the techniques available for reconstitution and analysis of ion channels in PLBs and discuss how the PLB technique has been, and may be, useful to the study of plant ion channels. 相似文献
62.
The involvement of a vanadate-sensitive ATPase in plasma membranes of a salt tolerant cyanobacterium
Rachel Gabbay-Azaria Uri Pick Gozal Ben-Hayyim Elisha Tel-Or 《Physiologia plantarum》1994,90(4):692-698
Plasma membranes of the marine cyanobacterium Spirulina subsalsa were tested for ATPase activity, and for involvement in salt stress. Transition of cells from saline to hypersaline medium enhances the respiratory activity associated with extrusion of Na+ and Cl− , and persisting salt stress induces synthesis of respiratory enzymes in the plasma membranes. The membranes possess an ATPase, specific for ATP and Mg2+ and sensitive to orthovanadate and dicyclohexylcarbodiimide. Immunoblot analysis of plasma membrane polypeptides from Spirulina subsalsa with anti- Arabidopsis H+ -ATPase serum identified a single polypeptide of 100 kDa, which cross-reacted with the antibodies. An unusual feature of this ATPase is a specific stimulation by Na+ ions. Prolonged adaptation of S. subsals cells to hypersaline conditions induced an increase in ATPase activity in subsequent plasma membrane preparations, as well as a higher content of the 100 kDa polypeptide. It is suggested that the ATPase investigated is an H+ -pump, which is involved in extrusion of Na+ and in conferring resistance to salt stress. 相似文献
63.
The activity of some phytotoxic metabolites of Pseudomonas syringae pv. syringae Van Hall strains B359 and B301 on in vivo and in vitro systems of H+-transport across the plasma membrane of maize (Zea mays L., hybrid Paolo) was investigated. In particular syringomycin, the first lipodepsinonapeptide isolated from Pss and already studied in plants and yeasts for its effects on several physiological systems, was compared with the recently described lipodepsipeptides with 22 or 25 amino acid residues, so called syringopeptins. The in vivo activity of the phytotoxins was tested on fusicoccin-stimulated H?-extrusion from cuttings of maize roots, which was inhibited by both types of toxins, with syringomycin more efficient than the syringopeptins. In vitro the H+-ATPase activity of predominantly right-side-out plasma membrane vesicles purified by two-phase partitioning was stimulated by 10 μM syringomycin and inhibited by higher levels, in agreement with the results of others with preparations of dicotyledons. Also the inhibition of the phosphohydrolytic activity of inside-out vesicles of mung bean plasma membrane was confirmed for maize. In both types of vesicles the syringopeptirts were better inhibitors than syringomycin. The pH gradient formed on addition of ATP to predominantly (25% latency) inside-out vesicles was immediately and completely collapsed by syringomycin and syringopeptins; H+-pumping was prevented if the toxins were added before ATP. The inhibition was concentration dependent, but at very low concentrations the effect was inverted. The results of the present investigation, carried out with maize preparations, confirm and extend the evidence so far obtained with dicotyledons in favour of the plasma membrane as an important site of interaction of syringomycin with the plant cell. They also indicate that, except for some details, the effects of syringopeptins at the level of the plasma membrane are the same as those of syringomycin. 相似文献
64.
Tomonari Tsutsumi Tetsuyuki Kobayashi Hiroshi Ueda Emiko Yamauchi Shiro Watanabe Harumi Okuyama 《Neurochemical research》1994,19(4):399-406
A membrane preparation from rat brain catalyzed the hydrolysis of [2-3H]glycerol-labeled lysophosphatidylinositol (lysoPI) to yield monoacylglycerol (MG) and inositolphosphates. This phospholipase C activity had an optimal pH of 8.2. The membrane preparation did not require the addition of Ca2+ for its maximum activity, but the activity was inhibited by addition of 0.1 mM EDTA to the assay mixture and was restored by simultaneous addition of 0.2 mM Ca2+. The activity was found to be localized in synaptic plasma membranes prepared by Ficoll and Percoll density gradients. The phospholipase C was highly specific for lysoPI; diacylglycerol formation from phosphatidylinositol, and MG formation from lysophosphatidylcholine, lysophosphatidylethanolamine, and lysophosphatidylserine were below 5% of that observed with lysoPI under the conditions used. We concluded that there is a pathway for phosphatidylinositol metabolism in brain synaptic membranes which is different from the well-characterized phosphoinositide-specific phospholipase C pathway.Abbreviations PI
phosphatidylinositol
- lysoPI
lysophosphatidylinositol
- lysoPI-PLC
lysophosphoinositide-specific phospholipase C
- PI-PLC
phosphoinositide-specific phospholipase C
- MG
monoacylglycerol
- PLC
phospholipase C
To whom to address reprint requests. 相似文献
65.
Synaptic plasma membranes (SPM) from the brain are known to have specific binding sites for several steroid hormones, but the mechanisms of membrane transduction of steroid signals is not understood. In this study, corticosterone was found to prevent temperature-dependent dissociation of endogenous calmodlin (CaM) from highly purified SPM from rat cerebral cortex. The steroid stabilizes Ca2+-dependent membrane binding of endogenous CaM (78% of total CaM), whereas Ca2+-independent binding of CaM (the other 22%) is not affected. The stabilization of membrane binding of endogenous CaM by corticosterone is concentration-dependent, with the maximal effect occurring at steroid concentration of 1 M. The EC50 is estimated as 130 nM, which is almost identical to the Kd of specific binding of the steroid to SPM (120 nM) reported previously. The effect in stabilizing membrane binding of CaM is specific to corticosterone and other glucocorticoids (cortisol, dexamethasone and triamcinolone); gonadal steroids (17-estradiol, progesterone and testosterone) are ineffective. Furthermore, corticosterone administration in vivo (2 mg/kg, i.p.) produced a rapid increase of CaM content in SPM, occurring within 5 min after steroid injection and persisting for at least 20 min. Since CaM mediates a variety of biochemical processes in synaptic membranes, we hypothesize that the effect of glucocorticoids in promoting membrane binding of CaM may lead to a cascade of consequences in synaptic membrane function.Special issue dedicated to Dr. Sidney Ochs. 相似文献
66.
Single Ca2+ channel records were obtained from plasma membrane-enriched fractions of wheat roots incorporated into artificial planar lipid bilayers. The channel had a unitary conductance of 15 pS for a 10 to 95 mM CaCl2 gradient (cytoplasm: outside of the cell). The voltage dependence displayed by the channel agreed with that expected for Ca2+ channels in the plasma membrane. The channel gating was strongly modified by addition of 20 M extracellular verapamil (a Ca2+ channel antagonist). Extracellular AlCl3 (70 M, pH 4.9) almost completely blocked the channel. 相似文献
67.
Plasma molybdenum concentrations were determined in children, ages two to 12 yr, with and without phenylketonuria (PKU). Mean
plasma molybdenum concentrations did not differ significantly between the children with PKU (1.33±0.5 μg/L) and without PKU
(1.75±0.8 μg/L). Plasma molybdenum concentrations in both groups of children ranged from <1 to 3 μg/L.
When data from all children were combined and then separated based on gender, mean plasma molybdenum levels did not differ
significantly between 9 females (1.56±0.68 μg/L) and 12 males (1.58±0.76 μg/L). Data were also combined and mean (±SD) plasma
molybdenum concentrations calculated for age groups. Two children aged 1 to <4 yr had plasma molybdenum concentrations of
1.0 μg/L, and six children aged 4 to <7 yr had mean (±SD) plasma molybdenum concentrations of 1.5±0.8 μg/L. Eleven children
aged 7 to <11 yr had a mean plasma molybdenum concentration of 1.7±0.7 μg/L, and two children 11 to <14 yr had plasma molybdenum
concentrations of 1 μg/L and 2 μg/L. Plasma molybdenum concentrations did not differ significantly among children in the age
groups. 相似文献
68.
Plasma and liver selenium of Wistar rats were determined after 1, 3, and 6 mo supplementation with 0.5, 2, 6, or 15 ppm selenium
as sodium selenite in drinking water. Plasma selenium was not different from control values at additional intake of 0.5 ppm
but increased above usual levels at higher intakes. A highly significant correlation was observed between the total quantity
of selenium ingested and plasma selenium after 1 mo treatment (r=0.99,p<0.01), but was less pronounced after 3 and 6 mo (0.94,p<0.05, and 0.78,p<0.05, respectively). The decrease in plasma selenium with time of treatment was more pronounced at higher intakes. There
was also a highly significant correlation between total selenium intake and liver selenium concentration (r=0.99,p<0.01) after 1 mo of treatment, but this time liver selenium did not change with time, and the correlation remained highly
significant throughout the investigation. Liver selenium therefore appears as a more sensitive and more representative measure
of selenium intake than plasma selenium. Most supplements did not affect body weight and survival of animals, except when
the diet was supplemented with 15 ppm for 6 mo; however, alterations in biochemical parameters concerning lipid status and
hepatic function were observed at levels above 2.0 ppm. 相似文献
69.
AProteinExtractedfromMouseSpermThatPlaysanImportantRoleinFertilizationZHUANGDa-zhong;(庄大中),ZHANGTian-yin(张天荫),CHENDa-yuan;(陈大... 相似文献
70.
烧伤狗浆血游离氨基酸的动态变化黎君友,周幼勤,赖业馥,赵有,伊少杰SequentialChangesinPlasmaFreeAminoAcidConcentrationinBurnedDogs¥Lijunyon;Zhouyouqin;Laiyefu;... 相似文献