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41.
Recognition of extracellular matrix components by neonatal and adult cardiac myocytes 总被引:14,自引:0,他引:14
The histogenesis of renal basement membranes was studied in grafts of avascular, 11-day-old mouse embryonic kidney rudiments grown on chick chorioallantoic membrane (CAM). Vessels of the chick CAM invade the mouse tissue during an incubation period of 7-10 days and eventually hybrid glomeruli composed of mouse epithelium and chick endothelium form. Formation of basement membranes during this development was followed by immunofluorescence and immunoperoxidase stainings using polyclonal and monoclonal antibodies against mouse and chick collagen type IV and against mouse laminin. These antibodies were species-specific as shown in immunochemical and immunohistologic analyses. The glomerular basement membrane contained both mouse and chick collagen type IV, demonstrating its dual cellular origin. All other basement membranes were either exclusively of chick origin (mesangium, vessels) or of mouse origin (tubuli, Bowman's capsule). 相似文献
42.
Glyphosate Inhibition of 5-Enolpyruvylshikimate 3-Phosphate Synthase from Suspension-Cultured Cells of Nicotiana silvestris 总被引:3,自引:3,他引:0 下载免费PDF全文
Treatment of isogenic suspension-cultured cells of Nicotiana silvestris Speg. et Comes with glyphosate (N-[phosphonomethyl]glycine) led to elevated levels of intracellular shikimate (364-fold increase by 1.0 millimolar glyphosate). In the presence of glyphosate, it is likely that most molecules of shikimate originate from the action of 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase-Mn since this isozyme, in contrast to the DAHP synthase-Co isozyme, is insensitive to inhibition by glyphosate. 5-Enolpyruvylshikimate 3-phosphate (EPSP) synthase (EC 2.5.1.19) from N. silvestris was sensitive to micromolar concentrations of glyphosate and possessed a single inhibitor binding site. Rigorous kinetic studies of EPSP synthase required resolution from the multiple phosphatase activities present in crude extracts, a result achieved by ion-exchange column chromatography. Although EPSP synthase exhibited a broad pH profile (50% of maximal activity between pH 6.2 and 8.5), sensitivity to glyphosate increased dramatically with increasing pH within this range. In accordance with these data and the pKa values of glyphosate, it is likely that the ionic form of glyphosate inhibiting EPSP synthase is COO−CH2NH2+CH2PO32−, and that a completely ionized phosphono group is essential for inhibition. At pH 7.0, inhibition was competitive with respect to phosphoenolpyruvate (Ki = 1.25 micromolar) and uncompetitive with respect to shikimate-3-P (Ki′ = 18.3 micromolar). All data were consistent with a mechanism of inhibition in which glyphosate competes with PEP for binding to an [enzyme:shikimate-3-P] complex and ultimately forms the dead-end complex of [enzyme:shikimate-3-P:glyphosate]. 相似文献
43.
The nucleoside sequence of tyrosine tRNA from Bacillus stearothermophilus. 总被引:2,自引:2,他引:0 下载免费PDF全文
R S Brown J R Rubin D Rhodes H Guilley A Simoncsits G G Brownlee 《Nucleic acids research》1978,5(1):23-36
The nucleotide sequence of tRNATyr from B. stearothermophilus has been determined: pG-G-A-G-G-G-G-s4U-A-G-C-G-A-A-G-U-Gm-G-C-U-A-A-m1A-C-G-C-G-G-C-G-G-A-C-U-Q-U-A-ms2i6A-A-psi-C-C-G-C-U-C-C-C-U-U-U-G-G-G-U-U-C-G-G-C-G-G-T-psi-C-G-A-A-U-C-C-G-U-C-C-C-C-C-U-C-C-A-C-C-AOH. A combination of classical fingerprinting methods, partial nuclease P1 digestion and two-dimensional homochromatography and a rapid "read off" sequencing gel technique were used to establish the complete nucleotide sequence. 相似文献
44.
Depletion of Mg2+ in the growth medium for chicken embryo fibroblasts produces a large decrease in DNA synthesis as measured by 3H-thymidine incorporation, and concomitant decreases in cellular K+ and Mg2+ and increases in Na+ and Ca2+. In cells grown in media containing 0.2 mM Ca2+, graded reduction of Mg2+ from 0.8 mM (control) to 0.016 mM produced graded decreases in DNA synthesis to 10% of control at 0.016 mM Mg2+. Concomitantly, cell cations showed graded changes, Na+ increasing to 227%, K+ decreasing to 52.5%, Mg2+ decreasing to 57.5% and Ca2+ increasing to 153.5% of control. The effects of Mg2+ depletion on DNA synthesis and cell cation content exhibited a dependence on Ca2+ concentration, the effects being larger at low Ca2+ concentration. Use of inorganic pyrophosphate in the growth medium as a selective complexor of Mg2+ caused a marked decrease in DNA synthesis which was accompanied by changes in cellular cation content similar to those produced by direct Mg2+ depletion. The effects of Mg2+ depletion on cell cation content are explainable in terms of changes in membrane permeability caused by rapid external surface exchange of bound divalent cations. Among the several interpretations of the data in terms of possible mechanisms by which changes in external Mg2+ concentration may affect cell metabolism, the most consistent with known properties of the system is the concept of a central role for intracellular free Mg2+ in the coordinate control of growth and metabolism in animal cells. 相似文献
45.
M. A. Moskowitz Deborah Rubin J. Liebschutz H. N. Munro T. S. Nowak R. J. Wurtman 《Journal of neurochemistry》1977,28(4):779-782
Abstract— l -DOPA or d -amphetamine administration disaggregates brain polyribosomes in animals maintained in an environment warm enough (26°C) so that the drugs concurrently elevate their body temperatures to above 39°C. The production of equivalent hyperthermia (by keeping control rats at ambient temperatures of 40–44° C) does not cause similar disaggregation of brain polysomes. Hence, the role of hyperthermia in the drug-induced disaggregation is permissive. 相似文献
46.
In the course of adapting O'Farrell's (1975, J. Biol. Chem.250, 4007–4021) two-dimensional separation technique for proteins to eukaryotic material, we have made some modifications. During sample preparation, sodium dodecyl sulfate (SDS) can be included, with a resulting enhancement in reproducibility of gel patterns. However, heating in the presence of SDS leads to artifactual spots in the gels, probably as a result of protein charge modifications. Ultracentrifugation reduces the clogging at the top of the isoelectric focussing gel. For electrophoresis, some modifications of apparatus and technique are suggested. For the analysis of gels, a simple high-efficiency method for the counting of radioactivity in spots from dried gel slabs is described. In addition, an inexpensive microdensitometer option is described for the analysis of the autoradiographs. Patterns of proteins obtained from superior cervical sympathetic ganglia of rats and from other eukaryotic tissues are illustrated. Finally, a few of the proteins commonly found in mammalian tissue are identified on the gels. 相似文献
47.
48.
Summary Transport, unidirectional flux, of a monosaccharide, a nucleoside and three amino acids, all of which enter cells by independent, discrete carriers, was compared at three stages of erythroid maturation, the normal (anucleate) mouse erythrocyte, and in differentiated and undifferentiated Friend erythroleukemia cells. We found specific transport alterations during this developmental program. Transport of 3-O-methylglucose increased with each successive developmental stage. Aminoisobutyrate transport was maintained during Friend cell differentiation, but fell slightly in erythrocytes. Leucine, lysine and uridine transport began to fall two days after dimethylsulfoxide exposure, and diminished further in red cells. These studies of transport are not directly comparable to uptake studies reported by others.Median cell volume and thus surface area decreased more during differentiation than amino acid transport declined, so flux, transport past a unit area of membrane, actually increased. Monosaccharide flux also increased. Only uridine transport fell in parallel to surface area. Perhaps sites for nutrient transport required for energy production are preferentially maintained. 相似文献
49.
A small tandem duplication is responsible for the unstable white-ivory mutation in Drosophila 总被引:13,自引:0,他引:13
The white-ivory (wi) mutation, an unstable allele of the white locus in Drosophila, reverts to wild-type at frequencies of 5 X 10(-5) in homozygous females, and 5 X 10(-6) in males and deletion heterozygous females. We show by molecular cloning and Southern blot analysis of DNA from wi flies that a 2.9 kilobase tandem duplication within the white locus is responsible for the mutation. Phenotypic reversion appears, in most cases, to be due to an exact excision of the extra copy of the sequence. Two derivative alleles of wi, one phenotypically wild-type, the other a partial revertant, carry insertions of moderately repetitive DNA from outside the locus, in addition to suffering deletions of some white locus DNA. Earlier genetic data preclude unequal crossing-over between homologs as an explanation for the precise reversions. Rather, an intrachromosomal meiotic event seems to be responsible. Our results suggest that intrachromosomal recombination may be responsible in other systems for a larger number of rearrangements than has been suspected, and that interallelic recombination frequencies in Drosophila do not always correlate in a simple way with DNA length or extent of homology. 相似文献
50.
The components of normal human serum (NHS) which bound DNA in a standard assay for anti-DNA antibody were characterized. IgG was the major detectable protein isolated from NHS by affinity chromatography on DNA-cellulose. A second adsorption of the whole serum IgG with DNA-cellulose did not remove additional gamma-globulin indicating that only a very small fraction of the IgG was capable of binding DNA. This binding activity was largely restricted to denatured DNA. IgG (Fab')2 bound DNA as well as the intact molecules demonstrating the antibody-like nature of the IgG binding. These results suggest that IgG antibody to denatured DNA is a normal component of human serum. 相似文献