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51.
Previous reports have suggested that the potentiation of cellular radiation sensitivity by hyperthermia may be due to its inhibition of the repair of single-strand breaks in DNA. Such inhibition could result in increased numbers of unrejoined breaks at long times following irradiation, lesions that are presumed to be lethal to the cell. As a test of this hypothesis, the amounts of residual strand-break damage in cells following combined hyperthermia and ionizing radiation were measured. The results show that hyperthermia does significantly enhance the relative number of unrejoined strand breaks as measured by the technique of alkaline elution and that the degree of enhancement is dependent on both the temperature and duration of the hyperthermia treatment. For example, compared to unheated cells, the proportion of unrejoined breaks measured 8 hr after irradiation was increased by a factor of 1.5 in cells that were treated for 30 min at 43 degrees C, by a factor of 6 for cells treated for 30 min at 45 degrees C, and by a factor of 4 for cells treated at 43 degrees C for 2 hr. In experiments in which the sequence of heat and irradiation were varied, a high degree of correlation was observed between the resulting level of cell killing and the relative numbers of unrejoined strand breaks. The greatest effects on both of these parameters were observed in those protocols in which the irradiation was delivered either during, just before, or just after the heat treatment. 相似文献
52.
The processing and collaborative assay of a reference endotoxin 总被引:7,自引:0,他引:7
H D Hochstein D F Mills A S Outschoorn S C Rastogi 《Journal of biological standardization》1983,11(4):251-260
A preparation of Escherichia coli bacterial endotoxin, the latest of successive lots drawn from bulk material which has been studied in laboratory tests and in animals and humans for suitability as a reference endotoxin, has been filled and lyophilized in a large number of vials. Details of its characterization, including stability studies, are given. A collaborative assay was conducted by 14 laboratories using gelation end-points with Limulus amebocyte lysates. Approximate continuity of the unit of potency with the existing national unit was achieved. The lot was made from the single final bulk but had to be freeze-dried in five sublimators. An assessment was therefore made for possible heterogeneity. The results indicate that the lot can be used as a large homogeneous quantity. The advantages of using it widely as a standard for endotoxins are discussed. 相似文献
53.
Structure of dorsal setae in the two-spotted spider-mite Tetranychus urticae Koch, 1836 总被引:1,自引:0,他引:1
L R Mills 《Acarologia》1974,15(4):649-658
54.
55.
R. A. Mills 《Bulletin of mathematical biology》1969,31(3):563-568
Changes in electrophoretic and/or electromagnetophoretic mobilities during the course of biochemical reactions are related
to first order rate constants of those reactions. By linearization of the mobility/reaction-coordinate relations, a method
for the determination of rate constants is suggested, an assessment being made of some likely advantages and limitations of
this approach to kinetic problems. 相似文献
56.
57.
Tryptophan Biosynthesis in Cell Cultures of Nicotiana tabacum 总被引:1,自引:1,他引:0
Some of the general features of the pathway for l-tryptophan biosynthesis in cell cultures of Nicotiana tabccum var. Wisc. 38 have been investigated. The results of both isotope competition and direct-labeling experiments show that shikimic acid, anthranilic acid, indoleglycerol phosphate, and indole can serve as precursors to l-tryptophan in these cells, indicating that, in terms of its biochemical intermediates, the pathway is similar to that described for the bacteria and fungi. 相似文献
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59.