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91.
Michael Ready Sandra Bird Gail Rothe J.D. Robertus 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,740(1):19-28
It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K+ and 3 mM Mg2+ retards the reaction, while 20 mM K+ and 2 mM Mg2+ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The Km for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pKa value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity. 相似文献
92.
Summary The properties of agglutination by plant lectins, along with chromosome patterns, were examined in a variety of mammalian
cell types. Untransformed adult and embryonic cells in culture, direct mouse spleen cell preparations, SV40-transformed 3T3
cells, and trypsinized 3T3 cells were all highly agglutinable with concanavalin A and with wheat germ agglutinin. In contrast,
untreated cells of the contact-inhibited 3T3 line were alone among the cells tested in their low agglutinability. Chromosome
analysis of the cultured cells showed that karyotypic variation from the diploid to an aneuploid state in mouse and rat embryo
cultures was not accompanied by a change in agglutinability. Adult rat lung, adult monkey kidney, and embryonic human lung
cells, which were all highly agglutinable, showed the normal diploid pattern. Thus, agglutination of cells by plant lectins
appears to be a cellular property often associated with non-neo-plastic cells.
This investigation was supported by Grants CA-12503 and ES-00260 from the National Institutes of Health, United States Public
Health Service. 相似文献
93.
Summary Auxin activity was detected in honeydew obtained from the aphid Tuberolachnus salignus (Gmelin) feeding on willow (Salix viminalis). Active uptake of 14C-indolyl-3-acetic acid (IAA) into the sieve tubes was demonstrated by irrigating the cambial surface of willow bark with 14C-IAA solution and assaying aphid stylet exudate. When, however, 14C-IAA was applied to the peridermal tissues of the bark or to a mature leaf most of the radioactivity (collected in honeydew or stylet exudate) co-chromatographed with indolyl-3-acetyl-aspartic acid (IAAsp). The presence of IAAsp in honeydew was not affected by extraction procedure or by aphid metabolism. Honeydew obtained from willow treated with 14C-tryptophan contained only 14C-tryptophan. When 14C-IAA was applied in agar to the cut end of willow segments the radioactivity was found to move in a basipetally polar manner. The direction of movement of radioactivity in the sieve tubes, however, was found to be influenced by the proximity of the roots. Nevertheless, there was evidence that endogenous auxin in the sieve tubes does move in a predominantly basipetal direction. 相似文献
94.
Structural Genes for a Newly Recognized Acetolactate Synthase in Escherichia coli K-12 总被引:23,自引:15,他引:8
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Maurilio De Felice John Guardiola Bruno Esposito Maurizio Iaccarino 《Journal of bacteriology》1974,120(3):1068-1077
Evidence is reported that shows the presence in Escherichia coli K-12 of a newly found acetolactate synthase. This enzyme is the product of two genes, ilvH and ilvI, both located very close to leu. Amber mutations have been found in both genes and therefore their products are polypeptides. Mutations in the ilvH gene cause the appearance of an acetolactate synthase activity which is relatively resistant to valine inhibition and can be separated by adsorption on hydroxylapatite from another activity present in the extract and more sensitive to valine inhibition than the former. A mutant altered in the ilvI gene was isolated among the revertants sensitive to valine inhibition of an ilvH mutant. Such a mutant lacks the resistant acetolactate synthase. A temperature-sensitive revertant of the ilvI mutant contained a temperature-sensitive acetolactate synthase. Thus ilvI is the structural gene for a specific acetolactate synthase. The activity of the ilvH gene product has been measured by adding an extract containing it to a purified ilvI acetolactate synthase, which, upon incubation, became more sensitive to valine inhibition. Conversely, a valine-sensitive acetolactate synthase (the product of the ilvH and the ilvI genes) became more resistant to valine inhibition upon incubation with an extract of a strain containing a missense ilvH gene product. 相似文献
95.
Effects of Dose on the Induction of Dominant-Lethal Mutations and Heritable Translocations with Ethyl Methanesulfonate in Male Mice 总被引:3,自引:2,他引:1
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W. M. Generoso W. L. Russell Sandra W. Huff Sandra K. Stout D. G. Gosslee 《Genetics》1974,77(4):741-752
Genetic damage by ethyl methanesulfonate (EMS) in male mice was measured at doses ranging from 50 to 300 mg/kg with dominant-lethal mutations and reciprocal translocations as endpoints. No appreciable increase in dominant-lethal mutations was detected following a dose of 100 mg/kg. Dominant lethals induced by EMS were convincingly detected only after a dose of 150 mg/kg, but in the translocation experiment an increase in the genetic effect was detectable at the 50 mg/kg dose. It is likely that dominant lethals had also been induced at the 50 and 100 mg/kg doses, but were not detected due to the relative insensitivity of the dominant..lethal procedure. Thus, for detection of low levels of EMS-induced chromosome breakage, translocations are a much more reliable endpoint than are dominant-lethal mutations. A procedure for large-scale screening of induced translocations is described.—The dominant-lethal dose-response curve, plotted on the basis of living embryos as a percentage of the control value, is clearly not linear as it is markedly concave downward. Similarly, the translocation dose-response curve showed a more rapid increase in the number of translocations with dose than would be expected on the basis of dose-square kinetics. It is clear for both of these endpoints that the effectiveness of EMS in inducing chromosome breakage is proportionately much lower at low doses. 相似文献
96.
Bruno Agostini 《Histochemistry and cell biology》1974,40(3):215-220
Summary Electron microscopy of negatively stained plasma shows that intravenous administration of heparin to healthy humans results in a fast degradation of very low density lipoproteins (VLDL), which are very rich in triglycerides (50% w/w). VLDL are also rapidly digested by post-heparin lipolytic activity when serum from non-heparinized subjects is incubated at 27°C in vitro with post-heparin serum of healthy controls.Abbreviations VLDL
very low density lipoproteins
- LDL
low density lipoproteins
- HDL
high density lipoproteins
- LP-X
lipoprotein-X, abnormal lipoprotein characterizing obstructive jaundice 相似文献
97.
The kinetics of denaturation of DNA have been studied by relaxation techniques. Examination of the terminal relaxation times for a variety of DNA's under a variety of conditions has shown that DNA denaturation is principally a hydrodynamically limited process. Measurements within the helix–coil transition have demonstrated that the experimentally measured terminal relaxation times are a function of the following: (1) position in the helix–coil transition; (2) ionic strength of the solvent; (3) solvent viscosity; (4) DNA concentration; (5) molecular weight; (6) number and position of single-strand breaks. The dependence of the terminal relaxation time on the above mentioned factors can be attributed to hydrodynamic effects. Thus a hydrodynamic model for DNA unwinding is required. The model which best fits the data involves the assumption of a rotational frictional coefficient independent of molecular weight. This assumption is suggested by the fact that the relaxation time is proportional to the first power of the molecular weight. 相似文献
98.
Zusammenfassung Die indirekten und direkten Flugmuskelfasern der Wanderheuschrecke enthalten parallel und voneinander getrennt verlaufende Myofibrillen. In den interfibrillären Räumen liegen zahlreiche, säulenförmig aneinandergereihte Mitochondrion, ein dichtes endoplasmatisches Retikulum und Tracheolen. In Höhe der A-I-Band-Grenzen befindet sich ein charakteristisches retikuläres System, dessen Queranordnung als Diade zu bezeichnen ist. Die chromatinreichen Kerne liegen peripher dicht unter dem Sarkolemm.Sowohl bei den indirekten als auch bei den direkten Flugmuskelgruppen kommt es im Verlaufe des Dauerfluges zu Transformationen der Mitochondrien, die sich in einer erheblichen Schwellung und in einer Umwandlung der Cristae zu Tubuli äußern. Diese Umwandlung wird als intramitochondriale Kompensation aufgefaßt, um das Verhältnis von Oberfläche der inneren membranösen Phase zum Volumen der inneren wäßrigen Phase — d. h. die spezifische Oberfläche — möglichst konstant zu halten. Eine Vesikulation der Tubuli könnte der morphologische Ausdruck für eine Dekompensation sein, da dann der Zusammenhang der äußeren wäßrigen Phase verlorengeht.Die Mitochondrien verschiedener Muskeln reagieren nicht synchron auf die Dauerbelastung, sondern ausgesprochen belastungs- und funktionsspezifisch: Zunächst transformieren sich die Mitochondrien der indirekten, dann erst die der direkten Flugmuskelgruppen, und der anfängliche Schwirrflug geht während fortschreitenden Dauerfluges in einen Flatterflug über. Die unterschiedlichen Erschöpfungszeitpunkte der indirekten Flugmuskeln werden durch die jeweils spezifische Funktion und die ontogenetische Entwicklung erklärt. 相似文献
99.
Bruno M. Cormier 《CMAJ》1966,94(6):276-291
A historical and psychological study of genocide is presented in which special emphasis is given to modern manifestations of this phenomenon. The policy of eradication of the Jews by the Hitler regime is considered as an example of genocide in the twentieth century. The psychopathology of genocide and the complex relationships among aggressors, victims and witnesses are elaborated. Inferences are drawn from past and present patterns of genocide that may provide some leads to the future. It is now possible to envisage an all-consuming genocide unless nations can learn to live together, not necessarily in unity but in diversity. 相似文献
100.
Sandra Pannell 《The Australian journal of anthropology》1989,19(3):160-169
…With metaphor we experience the metamorphosis of both language and reality. Paul Ricoeur. ‘Creativity in Language’. The Philosophy of Paul Ricoeur. pp. 132–133 (1973). 相似文献