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981.
Experiments were conducted to study the ability of irradiated glucose to induce reverse mutations in S. typhimurium by host-mediated assay. The results revealed no significant increase in the frequency of reverse mutations compared to controls. 相似文献
982.
Calcium channels. Gating for the physiologist 总被引:4,自引:0,他引:4
983.
984.
985.
B A Barres 《Nature》1989,339(6223):343-344
986.
DNA mutagenesis and recombination 总被引:10,自引:0,他引:10
The polymerase chain reaction is used for site-specific mutagenesis and for DNA recombination without any enzymatic reaction in vitro, apart from DNA amplification. 相似文献
987.
Among mycobacteria, Mycobacterium leprae is unique in its ability to oxidize a variety of diphenols to quinones in vitro. What physiologic role o-diphenoloxidase has in the organism remained unknown. Reducing substrates like NADPH, NADH and ascorbic acid reacted with the quinone formed from dopa (3,4-dihydroxyphenylalanine); the substrates were oxidized and the quinone was reduced back to diphenol in the process. Since the quinone undergoes reversible oxidation-reduction, diphenoloxidase might serve as an alternative respiratory mechanism in M. leprae for the utilization of other substrates, as has been reported in plants. 相似文献
988.
Inverse relationship of the durations of adjacent open and shut intervals for C1 and K channels 总被引:3,自引:0,他引:3
Ion channels in cell membranes, whether voltage-dependent or activated by ligands, make repeated transitions among open and shut states during activity. Information about the number of states and the transitional pathways between them can be obtained from the durations of open and shut intervals, as transitions to states of different lifetimes result in intervals of different mean durations. If there is only one open conformation, or state, then the durations of open intervals would be independent of the durations of adjacent shut intervals. On the other hand, if a channel has two or more open states with different mean lifetimes, and if each open state is entered directly from a different shut state with a different mean lifetime, then the open intervals should be related to the adjacent shut intervals. We now report that the durations of adjacent open and shut intervals for both a C1 channel and a large conductance Ca-activated K channel in skeletal muscle are inversely related; shorter open intervals are adjacent to longer shut intervals. These findings indicate that two or more shut states make direct transitions to two or more open states, and suggest that the lifetimes of adjacent open and shut states are inversely related. 相似文献
989.
Colcemid effects on homologue pairing and crossing over during fetal mouse oogenesis 总被引:1,自引:0,他引:1
G. Jagiello W. K. Sung J. -S. Fang M. B. Ducayen 《Cellular and molecular life sciences : CMLS》1989,45(5):482-484
Summary Colcemid was administered to gestational day 13 female mice to test effects on homologue pairing, synapsis and recombination of fetal oogenesis. Pairing abnormalities were detected in pachytene oocytes by light and electron microscopy examination of bivalents and synaptonemal complexes. Reduction of total chiasmata per treated diplotene oocyte (22.74) compared to controls (31.07) was found. 相似文献
990.
Multiple sclerosis is commonly associated with a local humoral immune response within the central nervous system. A hallmark of this intrathecal response is the presence of electrophoretically demonstrable oligoclonal bands of IgG in the cerebrospinal fluid (CSF) of up to 95% of patients. Observations indicating that a major part of the CSF IgG in some patients may represent antibodies to SV5, a simian virus closely related to human parainfluenza type 2 virus, were recently reported by Goswami et al. We have studied thirty patients with multiple sclerosis, but although we find intrathecal synthesis of IgG antibodies reacting with SV5 in seven of these, the antibodies were not associated with oligoclonal CSF IgG bands and could in each case be explained as potentially cross-reacting antibodies to other paramyxoviruses known to be human pathogens. We have therefore been unable to confirm that SV5 may be a major intrathecal immunogen in multiple sclerosis. 相似文献