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81.
Ana Maria Landeira-Fernandez Maricilia S. Costa Leopolde de Meis 《Bioscience reports》1996,16(6):439-451
Vesicles derived from maize roots retain a membrane bound H+-ATPase that is able to pump H+ at the expense of ATP hydrolysis. In this work it is shown that heparin, fucose-branched chondroitin sulfate and dextran sulfate 8000 promote a shift of the H+-ATPase optimum pH from 6.0 to 7.0. This shift is a result of a dual effect of the sulfated polysaccharides, inhibition at pH 6.0 and activation at pH 7.O. At pH 6.0 dextran 8000 promotes an increase of the apparent Km for ATP from 0.28 to 0.95 mM and a decrease of the Vmax from 14.5 to 7.1 mol Pi/mg · 30 min–1. At pH 7.0 dextran 8000 promotes an increase in Vmax from 6.7 to 11.7 mol Pi/mg · 30 min–1. In the presence of lysophosphatidylcholine the inhibitory effect of the sulfated polysaccharides observed at pH 6.0 was not altered but the activation of pH 7.0 decreased. It was found that in the presence of sulfated polysaccharides the ATPase became highly sensitive to K+ and Na+. Both the inhibition at pH 6.0 and the activation promoted by the polysaccharide were antagonized by monovalent cations (K+>Na+Li+).Abbreviations Mops
4-morpholinopropanesulfonic acid
- EDTA
ethylenediaminetetraacetic acid
- ACMA
9-amino-6-chloro-2-methoxyacridine
- FCCP
carbonyl cyanide p(trifluoromethoxy)-phenylhyrazone 相似文献
82.
83.
Retinoic acid-mediated activation of HNF-3 alpha during EC stem cell differentiation. 总被引:2,自引:0,他引:2 下载免费PDF全文
A Jacob S Budhiraja X Qian D Clevidence R H Costa R R Reichel 《Nucleic acids research》1994,22(11):2126-2133
84.
To dissect the cellular response to water stress and compare changes induced as a generalized response with those involved in tolerance/acclimation mechanisms, we analyzed changes in two-dimensional electrophoretic patterns of in vivo [35S]methionine-labeled polypeptides of cultured potato (Solanum tuberosum) cells after gradual and long exposure to polyethylene glycol (PEG)- mediated low water potential versus those induced in cells abruptly exposed to the same stress intensity. Protein synthesis was not inhibited by gradual stress imposition, and the expression of 17 proteins was induced in adapted cells. Some polypeptides were inducible under mild stress conditions (5% PEG) and accumulated further when cells were exposed to a higher stress intensity (10 and 20% PEG). The synthesis of another set of polypeptides was up-regulated only when more severe water-stress conditions were applied, suggesting that plant cells were able to monitor different levels of stress intensity and modulate gene expression accordingly. In contrast, in potato cells abruptly exposed to 20% PEG, protein synthesis was strongly inhibited. Nevertheless, a large set of polypeptides was identified whose expression was increased. Most of these polypeptides were not induced in adapted cells, but many of them were common to those observed in abscisic acid (ABA)-treated cells. These data, along with the finding that cellular ABA content increased in PEG-shocked cells but not in PEG-adapted cells, suggested that this hormone is mainly involved in the rapid response to stress rather than long-term adaptation. A further group of proteins included those induced after long exposure to both water stress and shock. Western blot analysis revealed that osmotin was one protein belonging to this common group. This class may represent induced proteins that accumulate specifically in response to low water potential and that are putatively involved in the maintenance of cellular homeostasis under prolonged stress. 相似文献
85.
Nielsen J; Peixoto AA; Piccin A; Costa R; Kyriacou CP; Chalmers D 《Molecular biology and evolution》1994,11(6):839-853
The region of the clock gene period (per) that encodes a repetitive tract
of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran
species both within and outside the Drosophilidae. All the non-
Drosophilidae sequences in this region are short and present a remarkably
stable picture compared to the Drosophilidae, in which the region is much
larger and extremely variable, both in size and composition. The
accelerated evolution in the repetitive region of the Drosophilidae appears
to be mainly due to an expansion of two ancestral repeats, one encoding a
Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and
asparagine or threonine. In some drosophilids the expansion involves a
duplication of the pentapeptide sequence, but in Drosophila pseudoobscura
both the dipeptide and the pentapeptide repeats are present in larger
numbers. In the nondrosophilids, however, the pentapeptide sequence is
represented by one copy and the dipeptide by two copies. These observations
fulfill some of the predictions of recent theoretical models that have
simulated the evolution of repetitive sequences.
相似文献
86.
Summary Thirty-three insertions of transposon Tn10l6l7 into genes involved in the control of rod cell shape were isolated in Salmonella typhimurium by the characteristic glossy appearance of colonies composed of spherical cells. Genetic tests demonstrated that 25 (76%) were insertions in the rodA gene, 7 (21 %) were mre mutants, and 1 (3%) was a divD mutant. No insertion in the pbpA gene were found. Insertions in cell shape genes only appeared when strains displaying resistance to mecillinam (not caused by -lactamase production) were employed. Neither rodA nor mre insertions could be transduced to wild-type strains but they were normally accepted by mecillinam-resistant derivatives and by cya and crp mutants, which, unlike the corresponding Escherichia coli strains, did not display resistance to mecillinam. On the other hand, the divD insertion could be efficiently transduced to any strain. It is concluded that the rodA, mre, and divD genes are involved in the control of rod cell shape but, in addition, the RodA and Mre products perform some function(s) that is essential for wild-type cells but dispensable for some mecillinam-resistant strains, and for cya and crp mutants. 相似文献
87.
Plants of Solanum tuberosum L. potato do not cold acclimate when exposed to low temperature such as 5°C, day/night. When ABA (45 M) was added to the culture medium, stem-cultured plantlets of S. tuberosum, cv. Red Pontiac, either grown at 20°C/15°C, day/night, or at 5°C, increased in cold hardiness from –2°C (killing temperature) to –4.5°C. The increase in cold hardiness could be inhibited in both temperature regimes if cycloheximide (70 M) was added to the culture medium at the inception of ABA treatment. Cycloheximide did not inhibit cold hardiness development, however, when it was added to the culture medium 3 days after ABA treatment.When pot-grown plants were foliar sprayed with mefluidide (50 M), ABA content increased from 10 nmol to 30 nmol g–1 dry weight and plants increased in cold hardiness from –2°C to about –3.5°C. The increases in free ABA and cold hardiness occurred only in plants grown at 20°C/15°C; neither ABA nor cold hardiness increased in plants grown at 5°C.The results suggest that an increase in ABA and a subsequent de novo synthesis of proteins are required for the development of cold hardiness in S. tuberosum regardless of temperature regime, and that the inability to synthesize ABA at low temperature, rather than protein synthesis, appears to be the reason why S. tuberosum does not cold acclimate. 相似文献
88.
A scanning electron microscope study of normal and vitrified leaves from Datura insignis plantlets cultured in vitro 总被引:5,自引:0,他引:5
Flavio Costa Miguens Ricardo Pereira Louro Raul Dodsworth Machado 《Plant Cell, Tissue and Organ Culture》1993,32(1):109-113
The surface anatomy of normal and vitreous leaves of plantlets obtained from Datura insignis Barb Rodr nodal segment cultures was compared using scanning electron microscopy. Normal and vitrified leaves are similar in several ways. They are both amphistomatic, and have similar distributions of glandular and non-glandular trichomes. Stomata have similar length, diameter and distribution in normal and vitreous plants. Immature stomata, which have closed pores, and plugged stomata, which contain an amorphous material between their guard cells, occur in both normal and vitrified leaves. Normal and vitreous leaves differ in the frequency of normal and abnormal stomata. Normal stomata have kidney-shaped guard cells and resemble closely those found in field-grown plants, whereas abnormal stomata have deformed guard cells. Normal stomata represent approximately 80% of the total number of stomata in normal leaves, but only 7% of the total number of stomata in vitreous leaves. Abnormal stomata represent 90% of the total number in vitreous leaves. The deformation of guard cells could possibly be a mechanical impediment to stomatal function. 相似文献
89.
Stimulation of Brain Pregnenolone Synthesis by Mitochondrial Diazepam Binding Inhibitor Receptor Ligands In Vivo 总被引:2,自引:0,他引:2
A. Korneyev B. S. Pan A. Polo E. Romeo A. Guidotti E. Costa 《Journal of neurochemistry》1993,61(4):1515-1524
Abstract: Evidence that neurosteroids are potent modulators of the action of GABA at GABAA receptors has prompted the investigation of the mechanism that controls brain neurosteroid synthesis by glial cell mitochondria in vivo. In vitro studies suggest that the interaction of the diazepam binding inhibitor (DBI)—a polypeptide that is abundant in steroidogenic cells—with glial mitochondrial DBI receptors (MDRs) is a crucial step in the physiological regulation of neurosteroid biosynthesis. MDRs bind 4-chlorodiazepam (4′-CD), N,N-di-n-hexyl-2-(4-fluorophenyl)-indol-3-acetamide (FGIN-1–27), and the isoquinoline carboxamide PK 11195 with high affinity, and these ligands have been used to investigate whether the stimulation of glial MDRs increases brain pregnenolone production in vivo. Adrenalectomized and castrated (A-C) male rats (to eliminate peripheral sources of pregnenolone) were pretreated with trilostane (to prevent pregnenolone metabolism to progesterone), and the pregnenolone content in brain regions dissected after fixation with a 0.8-s exposure to microwave irradiation focused to the head was determined by HPLC followed by specific radioimmunoassay. The forebrain and cerebellum of A-C rats contained 4–7 ng of pregnenolone/g of tissue, and the olfactory bulb contained 10–14 ng/g. These concentrations of brain pregnenolone are only 30–40% lower than those of shamoperated rats. In contrast, the plasma pregnenolone content of sham-operated rats was 2–3 ng/ml, but it was only 0.15–0.20 ng/ml in the plasma of A-C rats. In A-C rats, treatment with the MDR ligands 4-CD and FGIN-1–27 increased the pregnenolone content in the brain but failed to change the plasma or peripheral tissue content of this steroid. The effect of 4′-CD on brain pregnenolone content was maximal (70–100% increase) at the dose of 18 μmol/kg, 5–10 min after intravenous injection. The effect of oral administration of FGIN-1–27 on brain pregnenolone content was maximal (80–150% increase) at doses of 400–800 μmollkg and peaked at ~ 1 h. That this effect of FGIN-1–27 was mediated by the MDR was documented by pre-treatment with the MDR partial agonist PK 11195 (100 μmol/kg, i.p.). PK 11195 did not affect basal brain pregnenolone content but prevented the accumulation of brain pregnenolone induced by FGIN-1–27. FGIN-1–27 and 4-CD failed to increase the brain concentration of dehydre epiandrosterone in A-C rats. These data suggest that glial cell MDRs play a role in neurosteroid biosynthesis in vivo. 相似文献
90.
Barium permeability of neuronal nicotinic receptor alpha 7 expressed in Xenopus oocytes. 总被引:2,自引:2,他引:0 下载免费PDF全文
The rat alpha 7 neuronal nicotinic acetylcholine receptor was expressed and studied in Xenopus oocytes. The magnitude and reversal potential of instantaneous whole cell currents were examined in solutions containing varying concentrations of either calcium or barium, and in the presence or absence of the intracellular calcium chelator BAPTA. In external barium, application of nicotine elicits an inwardly rectifying response; in calcium the response is larger and has a linear IV relation. Pretreatment of oocytes with BAPTA-AM could not prevent activation of calcium-dependent chloride channels in external Ringer containing calcium. Using an extended GHK equation, the permeability ratio PBa/PNa of the alpha 7 receptor was determined to be about 17. Our results suggest that alpha 7 nicotinic receptors are highly permeable to divalent cations. 相似文献