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91.
Differential expression of K+ channel mRNAs in the rat brain and down-regulation in the hippocampus following seizures. 总被引:4,自引:0,他引:4
K+ channels are major determinants of membrane excitability. Differences in neuronal excitability within the nervous system may arise from differential expression of K+ channel genes, regulated spatially in a cell type-specific manner, or temporally in response to neuronal activity. We have compared the distribution of mRNAs of three K+ channel genes, Kv1.1, Kv1.2, and Kv4.2 in rat brain, and examined activity-dependent changes following treatment with the convulsant drug pentylenetetrazole. Both regional and cell type-specific differences of K+ channel gene expression were found. In addition, seizure activity caused a reduction of Kv1.2 and Kv4.2 mRNAs in the dentate granule cells of the hippocampus, raising the possibility that K+ channel gene regulation may play a role in long-term neuronal plasticity. 相似文献
92.
Eyvind J. Paulssen Ruth H. Paulssen Kaare M. Gautvik Jan O. Gordeladze 《Cellular signalling》1992,4(6):747-755
We have investigated the possibility that adenylyl cyclase (AC) activity and membrane protein levels of the -subunits of the stimulatory and inhibitory G-proteins of AC (Gs and Gi−2) in cultured prolactin-producing rat pituitary adenoma cells (GH3 cells) are modulated by phospholipase C (PLC)-generated second messengers. Pretreatment of cells (6–48 h) with ionomycin (1 μM) or 1-oleoyl-2-acetylglycerol (OAG; 1μM) showed that ionomycin regulated Gs levels in a time-dependent, biphasic manner; a two-fold increase followed a 40% initial reduction, while OAG lowered Gs levels by more than 50% at all time-points. Gi−2 levels remained unchanged by both pretreatments. OAG, but not ionomycin, increased basal AC activity without increasing enzyme protein levels. Alterations in AC responsiveness to peptide hormones (e.g. thyroliberin and vasoactive intestinal peptide) correlated to membrane Gs protein -subunit content. These results demonstrate the involvement of G-protein translation regulation as one mechanism of ‘cross-talk’ between the PLC- and AC-dependent signalling pathways. 相似文献
93.
Viability measurements of hybridoma cells in suspension cultures 总被引:1,自引:0,他引:1
José M. Coco-Martin Jan W. Oberink Tiny A. M. van der Velden-de Groot E. Coen Beuvery 《Cytotechnology》1992,8(1):57-64
Several methods were applied to determine the viability of hybridoma cells in suspension. These methods include dye inclusion
and exclusion assays such as the classical trypan blue exclusion assay, the propidium iodide (PI) exclusion assay and the
fluorescein diacetate (FDA) inclusion assay. Furthermore, the relation was studied between release of lactate dehydrogenase
(LDH) by hybridoma cells and their viability. Also the ATP content of the cells and cellular heterogeneity as measured with
a flow cytometer were determined in relation to cellular viability.
The dye inclusion and exclusion assays using trypan blue, FDA, PI were shown to be useful methods to determine cellular viability.
With the FDA and PI methods it was possible to obtain additional information about cells which are in a transition state between
viable and non-viable. The viability according to the scatter properties of the cells appears to reflect the overall condition
of the cells, although interpretation of the results is difficult. Measurement of LDH release in the culture fluid or the
cytoplasmic ATP content could not be used as parameters for cell viability. 相似文献
94.
Signal peptidase I overproduction results in increased efficiencies of export and maturation of hybrid secretory proteins in Escherichia coli 总被引:4,自引:0,他引:4
Jan Maarten van Dijl Anne de Jong Hilde Smith Sierd Bron Gerard Venema 《Molecular & general genetics : MGG》1991,227(1):40-48
Summary The effects of 25-fold overproduction ofEscherichia coli signal peptidase I (SPase I) on the processing kinetics of various (hybrid) secretory proteins, comprising fusions between
signal sequence functions selected from theBacillus subtilis chromosome and the mature part of TEM-β-lactamase, were studied inE. coli. One precursor (pre[A2d]-β-lactamase) showed an enhanced processing rate, and consequently, a highly improved release of
the mature enzyme into the periplasm. A minor fraction of a second hybrid precursor (pre[Al3i]-β-lactamase), which was not
processed under standard conditions of SPase I synthesis, was shown to be processed under conditions of SPase I overproduction.
However, this did not result in efficient release of the mature β-lactamase into the periplasm. In contrast, the processing
rates of wild-type pre-β-lactamase and pre(A2)-β-lactamase, already high under standard conditions, were not detectably altered
by SPase I overproduction. These results demonstrate that the availability of SPase I can be a limiting factor in protein
export inE. coli, in particular with respect to (hybrid) precursor proteins showing low (SPase I) processing efficiencies. 相似文献
95.
Beinsberger Susy E. I.; Valcke Roland L. M.; Deblaere Rolf Y.; Clijsters Herman M. M.; De Greef Jan A.; Van Onckelen Henri A. 《Plant & cell physiology》1991,32(4):489-496
Transformation of tobacco leaf discs with the cytokininipt gene yielded several transgenic callus tissue lines, respectiveto the kind of ipt construction present in the A. tumefacienscointegrates. Those calli containing an active ipt gene wereable to grow hormone-autotrophically and showed an increasedendogenous cytokinin level in comparison with controls. Analysisof endogenous IAA level did not allow any quantitative correlationwith the cytokinin content. However, a minimal level of auxinseems to be necessary to obtain hormone-autotrophic growth.Exogenously supplied NAA significantly reduced the endogenouscytokinin content without modifying growth characteristics. The varying chlorophyll content in the different callus lineselicited the study of the ultrastructure of the plastids. Thecontrols contained small plastids, often filled with starchor accumulated vesicles that did not allow observation of theinternal membrane system. The Pssu-ipt line, havinga higher cytokinin content, showed plastids with an internalmembrane system consisting of stroma and grana thylakoids, butthis structure was lost during subculture. Swollen thylakoidsappeared, the amount of starch was reduced and vesicles wereaccumulating. (Received November 15, 1990; Accepted March 4, 1991) 相似文献
96.
The effects of inoculum level and lime-pelleting were studied in an acid soil with respect to the nodulation and growth of
lucerne (Medicago sativa cv Resis) and the population dynamics of Rhizobium meliloti. In small root-boxes (rhizotrons), the in-situ survival of inoculated rhizobia was studied in the micro-environment around the seed for a period of 12 days after sowing.
During the initial 24 hours, a strong increase in rhizobial numbers was measured, concomitantly with the development of roots.
As a result of lime-pelleting, rhizobial numbers were higher only at 3 days after sowing (P<0.05). Later, this difference diminished steadily. Addition of lime did not increase the adhesion of the rhizobia to the
seedling tap root.
Plant responses to inoculation were studied in pots. To obtain optimal nodulation, the soil had to be neutralized around the
seed with lime and at least 105 cells of R. meliloti were required. With more than 105 rhizobia per seed, lime-pelleting increased the number of crown-nodulated seedlings from 24% to 77%. Higher numbers of rhizobia
could not compensate the effect of lime. A strong correlation was found between crown nodulation, nitrogen content and dry
weight of the shoots. 相似文献
97.
Role of neurogenic genes in establishment of follicle cell fate and oocyte polarity during oogenesis in Drosophila 总被引:16,自引:0,他引:16
Oogenesis in Drosophila involves specification of both germ cells and the surrounding somatic follicle cells, as well as the determination of oocyte polarity. We found that two neurogenic genes, Notch and Delta, are required in oogenesis. These genes encode membrane proteins with epidermal growth factor repeats and are essential in the decision of an embryonic ectodermal cell to take on the fate of neuroblast or epidermoblast. In oogenesis, mutation in either gene leads to an excess of posterior follicle cells, a cell fate change reminiscent of the hyperplasia of neuroblasts seen in neurogenic mutant embryos. Furthermore, the Notch mutation in somatic cells causes mislocalization of bicoid in the oocyte. These results suggest that the neurogenic genes Notch and Delta are involved in both follicle cell development and the establishment of anterior-posterior polarity in the oocyte. 相似文献
98.
Lisbeth B. Møller Jim Kaufman Sten Verland Jan Salomonsen David Avila John D. Lambris Karsten Skjødt 《Immunogenetics》1991,34(2):110-120
Molecular variation among major histocompatibility complex (MHC) class I (B-F) proteins from B-homozygous chickens is apparently caused by C-terminal variation. Analysis of the total B-F protein pool revealed substantial heterogeneity with two or three molecular mass constituents, each being comprised by several isoelectric focusing variants. This heterogeneity could not be reduced by enzymatic deglycosylation. By contrast, proteolytic removal of a small (M
r 1000–4000) fragment from the chain resulted in the generation of a M
r 36 000 fragment, common to all the molecular mass variants. Unlike the parent proteins, the M
r 36 000 fragment derived from isolated variants yielded identical, simple patterns in two-dimensional gel electrophoresis and identical finger prints in peptide mapping. This, together with N-terminal amino acid sequencing, as well as comparison of hydrophobicity properties of fragments obtained by gradual proteolytic digestion, indicated that the small peptide responsible for the major B-F heterogeneity was situated in the intracellular, C-terminal part. 相似文献
99.
High-affinity binding of3H-folate in Triton X-100 solubilized membranes of human liver displayed characteristics, e.g. apparent positive cooperativity, which are typical of specific folate binding. Ultrogel® AcA 44 chromatography of solubilized membranes saturated with3H-folate revealed a major peak of 100 kDa and a minor peak of 25 kDa. The 100 kDa peak could represent a hydrophobic membrane associated molecular form of the protein. This notion was supported by the fact that the two peaks had identical molecular weights as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis with immunoblotting. 相似文献
100.
Rapid and simple isolation of pure photosystem II core and reaction center particles from spinach 总被引:2,自引:2,他引:0
Peter J. van Leeuwen Maaike C. Nieveen Erik Jan van de Meent Jan P. Dekker Hans J. van Gorkom 《Photosynthesis research》1991,28(3):149-153
Pure and active oxygen-evolving PS II core particles containing 35 Chl per reaction center were isolated with 75% yield from spinach PS II membrane fragments by incubation with n-dodecyl--D-maltoside and a rapid one step anion-exchange separation. By Triton X-100 treatment on the column these particles could be converted with 55% yield to pure and active PS II reaction center particles, which contained 6 Chl per reaction center.Abbreviations Bis-Tris
bis[2-hydroxyethyl]imino-tris[hydroxymethyl]methane
- Chl
chlorophyll
- CP29
Chl a/b protein of 29 kDa
- Cyt b
559
cytochrome b
559
- DCBQ
2,5-dichloro-p-benzo-quinone
- LHC II
light-harvesting complex II, predominant Chl a/b protein
- MES
2-[N-Morpholino]ethanesulfonic acid
- Pheo
pheophytin
- PS H
photosystem II
- QA
bound plastoquinone, serving as the secondary electron acceptor in PS II (after Pheo)
- SDS
sodiumdodecylsulfate 相似文献