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1.
The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H+ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation. 相似文献
2.
The biological effects of three furocoumarins on the proliferation of human normal peripheral blood lymphocytes have been investigated. Mitogen-stimulated human lymphocytes were assayed "in vitro" by measuring 3H-thymidine (3H-TdR) incorporation in the presence and in the absence of 15-30 microM 3-carbethoxypsoralen (3-CPs), trimethylangelicin (TMA) and psoralen (PSR) with and without UV-A irradiation (365 nm). The three furocoumarins differ in their ability to form mono- and bi-functional adducts with DNA pyrimidine bases and in producing reactive species of oxygen. At low furocoumarin doses and short times of UV-A irradiation (15-30 sec) used in the present study, 3-CPs did not affect 3H-TdR incorporation in PHA-stimulated human lymphocytes, TMA strongly inhibited 3H-TdR incorporation, while, unexpectedly, PSR increased 3H-TdR incorporation in the absence of irradiation, likely acting, under these experimental conditions, as a co-mitogen. 相似文献
3.
Khalid M. Chraibi B Jean-Claude Castelle Alain Latche Jean-Paul Roustan Jean Fallot 《Plant cell reports》1992,10(12):617-620
We describe here a liquid culture system for the regeneration of shoots at high frequencies from mature cotyledon tissues of three genotypes of sunflower (Helianthus annuus L.) one of which had previously been found to be recalcitrant to regeneration when cotyledons were cultured on solid medium. Cotyledons were excised from 2-day-old seedlings and incubated in liquid Murashige and Skoog's modified medium supplemented with 5.4 M naphthaleneacetic acid (NAA) and 4.4 M benzylaminopurine (BAP). After two weeks in culture, the whole upper surface of regenerating explants was covered with green shootlets. The percentages of regenerating explants of three genotypes varied between 60 and 70%, and the number of shoots per regenerating explant was highly increased. The shootlets were transferred to solid Murashige and Skoog's medium allowing shoot development, then to rooting medium. Rooted plantlets were successfully acclimatized and gave fertile plants. The role of liquid medium culture in the induction of sunflower regeneration is discussed.Abbreviations BAP
6-benzylaminopurine
- NAA
1-naphthaleneacetic acid
- IAA
indole-3-acetic acid
- IBA
indole-3-butyric acid 相似文献
4.
Khalid Ahmed Peter H. van der Meide John L. Turk 《Cancer immunology, immunotherapy : CII》1989,30(4):213-218
Summary Some conventional and experimental anticancer drugs were tested for their effect on concanavalin-A-induced interferon release from rat splenocytes in vitro. When 2.5 × 106 rat splenocytes/ml, stimulated with 1 µg/ml concanavalin A, were incubated with various non-cytotoxic doses of the vinca alkaloid vincristine, there was an inhibition of the release of interferon in culture supernatants. The antitumour antibiotics bleomycin and Adriamycin, alkylating agents 4-hydroperoxycyclophosphamide and mafosfamide, and the immunoactive peptides FK 156 and FK565 did not affect the release of interferon under similar conditions. However, cyclosporin A, in similar experiments, markedly inhibited the release of interferon . 相似文献
5.
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7.
Ali Arslan Cuillermina Almazan Hans H. Zingg 《In vitro cellular & developmental biology. Animal》1995,31(2):140-148
Summary Normal and neoplastic growth of epithelial cells depends on mutual interactions between epithelial and stromal cells. As a
tool for the study of the underlying molecular mechanisms, we have developed temperature-sensitive, nontransformed cell lines
derived from rat uterine epithelium and stroma by transfecting primary cultures with a temperature-sensitive mutant of the
SV40 large T antigen. The epithelial and stromal cell lines obtained shared relevant morphological characteristics with the
primary cells from which they were derived. Immunocytochemical analysis showed that the epithelial cell lines expressed the
intermediate filament cytokeratin, whereas the stromal lines expressed the intermediate filament vimentin. Alkaline phosphatase
activity was present in all cell lines examined. All cell lines were anchorage dependent and did not form foci. One epithelial
cell line expressed oxytocin mRNA, a gene product recently shown to be highly expressed in vivo in the uterine epithelium
at term. If grown on Matrigel, this cell line formed domelike structures, a further characteristic of its differentiated phenotype.
In an attempt to reconstitute an endometrium in vitro, epithelial cells were seeded on top of a layer of stromal cells. Paraffin
cross sections showed that this in vitro system consisted of a bilayer structure. Four to five cuboidal epithelial cells were
typically anchored atop one stromal cell, forming an endometriumlike tissue. The present in vitro system should provide a
useful model for further studies on endometrial functions and epithelial/stromal cell interactions at a molecular level. 相似文献
8.
Richard Wales Hazel C. Gorham Khalid Hussain Lynne M. Roberts J. Michael Lord 《Glycoconjugate journal》1994,11(4):274-281
Deleted forms of ricin B chain (RTB) containing only one of the two galactose binding sites were produced inE. coli and targeted to the periplasm by fusion to theompA orompF signal sequences. The proteins were then isolated from the periplasm and their sugar binding properties assessed. Previous studies investigating the properties of such proteins produced inXenopus laevis oocytes suggested that deleted forms of RTB, when not glycosylated, retain their ability to bind simple sugars, unlike the full-length unglycosylated proteins. When produced inE. coli however we found that only one, EB733, of a number of deleted forms of RTB closely related to those previously produced inXenopus laevis oocytes, bound to simple sugars. All of the deletion forms of RTB were found to bind in the asialofetuin binding assay; an assay which has been previously utilized to measure binding of lectins to the terminal galactose residues of glycoprotein oligosaccharides. However, in contrast to glycosylated RTB, binding of the deletion mutants could be competed to only a small degree or not at all with galactose. The only deletion mutant observed to bind to free galactose when produced inE. coli corresponded closely to the complete domain 2 of RTB. It is assumed that this mutant forms a stable structure similar to that of the C-terminal domain in the full-length protein. The structural integrity of EB733 was not only suggested by its sugar binding properties and solubility but also by its consistently higher level of expression and the absence of any apparent susceptibility toE. coli proteases.Abbreviations RTA
ricin toxin A chain
- RTB
ricin toxin B chain
- ER
endoplasmic reticulum
- SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis
- IPTG
isopropyl -d-thiogalactopyranoside 相似文献
9.
Keisuke Tsutsumi Masami Niwa Naoki Kitagawa Sei-ich Yamaga Takeo Anda †Akihiko Himeno ‡Takaya Sato Humayun Khalid Kohtaro Taniyama Shobu Shibata 《Journal of neurochemistry》1994,63(6):2240-2247
Abstract: We identified and characterized 125I-endothelin-1 (125I-ET-1) binding sites in tumor capillaries isolated from human glioblastomas, using the quantitative receptor autoradiographic technique with pellet sections. Quantification was done using the computerized radioluminographic imaging plate system. High-affinity ET receptors were localized in capillaries from glioblastomas and the surrounding brain tissues (KD = 4.7 ± 1.0 × 10?10 and 1.6 ± 0.3 × 10?10M, respectively; Bmax = 161 ± 38 and 140 ± 37 fmol/mg, respectively; mean ± SEM, n = 5). BQ-123, a selective antagonist for the ETA receptor, potently competed for 125I-ET-1 binding to sections of the microvessels with IC50 values of 5.1 ± 0.3 and 5.1 ± 1.5 nM, and 10?6M BQ-123 displaced 84 and 58% of ET binding to capillaries from tumors and brains, respectively. In addition, competition curves obtained in the presence of increasing concentrations of ET-3 showed two components (IC50 = 5.7 ± 2.5 × 10?10 and 1.4 ± 0.2 × 10?6M for tumor microvessels, 1.8 ± 0.6 × 10?10 and 1.1 ± 0.3 × 10?6M for brain microvessels, respectively). Our results indicate that (a) the method we used is simple and highly sensitive for detecting and characterizing various receptors in tumor capillaries, especially in the case of a sparse specimen, and (b) capillaries in glioblastomas express specific high-affinity ET binding sites, candidates for biologically active ET receptors, which predominantly belong to the ETA subtype. 相似文献
10.
Analysis of γ-Aminobutyric AcidA Receptor Subunits in the Mouse Cochlea by Means of the Polymerase Chain Reaction 总被引:1,自引:0,他引:1
Dennis G. Drescher Glenn E. Green Khalid M. Khan† Kavita Hajela Kirk W. Beisel Barbara J. Morley Anil K. Gupta 《Journal of neurochemistry》1993,61(3):1167-1170
Abstract: Unlike 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces consistent decreases in levels of striatal dopamine (DA) with considerably smaller and more variable effects on mouse brain levels of serotonin (5-HT) and norepinephrine (NE), a novel amine-substituted MPTP analogue, 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2 -MPTP), administered in a standard mouse dosing paradigm for MPTP (20 mg/kg X 4) did not affect striatal DA but led to marked reductions (60–70%) in levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and NE measured in frontal cortex and hippocampus 1 week after treatment. Another 2'-substituted MPTP analogue, 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine, affected cortical and hippocampal 5-HT, 5-HIAA, and NE only minimally, while markedly reducing the DA content in striatum (90%), thus indicating that the substituent (-NH2 versus -CH3 ) at the 2'position is important for the differential effects of these MPTP analogues. In a replication study with a 3-week end point, hippocampal and cortical 5-HT, 5-HIAA, and NE levels remained depressed with no indication of recovery. These results suggest that 2'-NH2 -MPTP may be a novel, regionally selective neurotoxin for serotonergic and norad-renergic nerve terminals. 相似文献