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921.
A common DNA religation assay for topoisomerase II takes advantage of the fact that the enzyme can rejoin cleaved nucleic acids but cannot mediate DNA scission at suboptimal temperatures (either high or low). Although temperature-induced DNA religation assays have provided valuable mechanistic information for several type II enzymes, high-temperature shifts have not been examined for human topoisomerase IIalpha. Therefore, the effects of temperature on the DNA cleavage/religation activity of the enzyme were characterized. Human topoisomerase IIalpha undergoes two distinct transitions at high temperatures. The first transition occurs between 45 and 55 degrees C and is accompanied by a 6-fold increase in the level of DNA cleavage at 60 degrees C. It also leads to a loss of DNA strand passage activity, due primarily to an inability of ATP to convert the enzyme to a protein clamp. The enzyme alterations that accompany the first transition appear to be stable and do not revert at lower temperature. The second transition in human topoisomerase IIalpha occurs between 65 and 70 degrees C and correlates with a precipitous drop in the level of DNA scission. At 75 degrees C, cleavage falls well below amounts seen at 37 degrees C. This loss of DNA scission appears to result from a decrease in the forward rate of DNA cleavage rather than an increase in the religation rate. Finally, similar high-temperature alterations were observed for yeast topoisomerase II and human topoisomerase IIbeta, suggesting that parallel heat-induced transitions may be widespread among type II topoisomerases. 相似文献
922.
G. N. Borisyuk R. M. Borisyuk A. B. Kirillov E. I. Kovalenko V. I. Kryukov 《Biological cybernetics》1985,52(5):301-306
A new method is proposed to analyse dependencies in point processes, which takes into account specific character of neuronal activity. Simulation modelling of neuronal network revealed that the estimated weight of connection depends monotonically on the value of the model synaptic strength. In contrast to the crosscorrelation, the method allows for nonlinear interconnections and does not require point processes to be stationary and samples to be large. Examples are presented of the method's application to neurophysiological data analysis. 相似文献
923.
The first appearance, the 12-year follow-up, and the autopsy of a patient with a strange soft-tissue tumor in the lower leg region are described. Although it was originally taken for a malignant synovial tumor, its peculiar distribution pattern, together with its histologic picture, confirmed the final diagnosis as an epithelioid sarcoma. 相似文献
924.
Amy Chapman Gonzalo Gonzales Wayne R. Burrowes Paul Assanah Bernadette Iannone Michael K. Leung George B. Stefano 《Cellular and molecular neurobiology》1984,4(2):143-155
In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals. The decrease in the high-affinity binding site density and the corresponding increase in endogenous enkephalin levels suggest the existence of an opioid compensatory mechanism associated with the aging process. In Mytilus there is a demonstrated decrease with age in intraganglionic dopamine levels in response to applied opiates. In addition, the inhibition of dopamine-stimulated adenylate cyclase activity by opiates also decreases in older animals. In Leucophaea the sex difference in opioid binding densities diminishes with age. 相似文献
925.
A A Krichevskaia A I Lukash N V Pushkina I V Shepotinovskaia K B Sherstnev 《Nauchnye doklady vysshe? shkoly. Biologicheskie nauki》1984,(7):23-28
The amide content of total proteins and protein fractions (alpha-, beta-, gamma-cristallins and albuminoid) from cortex and nuclear lens zones of cattle has been investigated. The amide content in proteins of cortex and nuclear lens of young animals (1,5-2 years old) is the same. The decrease of the amide content in the proteins of nuclear lenz zone of old animals (6-12 years old) is due to fraction of readily hydrolysed amides. The data obtained prove the posttranslational desamidation of lens proteins at ageing. beta-Cristallines--the proteins with the highest amides content is exposed to posttranslational desamidation most of all. 相似文献
926.
927.
928.
929.
Inhibitory effect of ammonium chloride and chloroquine on the entry of the toxic lectin modeccin into HeLa cells 总被引:12,自引:0,他引:12
Ammonium chloride and chloroquine protected a variety of cell lines against diphtheria toxin and the toxic lectin modeccin. Experiments where the ability of antibody to neutralize the toxin was measured indicate that in the presence of ammonium chloride and chloroquine, modeccin remains at the cell surface and that the two compounds inhibit the uptake of modeccin into the cytoplasm. A cell line tolerating increased concentrations of modeccin was not protected against modeccin by ammonium chloride or chloroquine, whereas the compounds did protect these cells against diphtheria toxin. 相似文献
930.
A. V. Andriyash D. A. Vikhlyaev D. A. Dmitrov A. L. Zapysov A. G. Kakshin I. A. Kapustin E. A. Loboda V. A. Lykov A. V. Potapov V. A. Pronin V. N. Sanzhin V. N. Saprykin A. A. Ugodenko O. V. Chefonov M. N. Chizhkov 《Plasma Physics Reports》2006,32(2):135-137
Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 1018 W/cm2 in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors. 相似文献