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941.
R. H. L. DISNEY 《Systematic Entomology》1986,11(4):413-422
ABSTRACT. Diplonevra mortimeri sp.nov. and D.watsoni. sp.nov. are described from specimens caught at Nasutitermitinae termite colonies in Sulawesi. The female of both species has a remarkable pre-oviposition behaviour in which she lures a worker termite into following her away from the colony. She then oviposits in the termite's abdomen. Pupation takes place within the remains of the host's abdomen. Both species only mature a single egg at a time. The female probably guards the comatose host termite during the period of larval development. The morphology of the male hypopygia of the new species allows reinterpretation of the peculiar anal tube in typical male Diplonevra. Furthermore the suggested homologies reinforce the view that the epandrium (tergite 9) has not been replaced by a periandrium (fused gonocoxites) in the Cyclorrhapha and consequently the latter cannot be derived from the Empidoidea. 相似文献
942.
Viscoelasticity of packed erythrocyte suspensions subjected to low amplitude oscillatory deformation. 下载免费PDF全文
Concentrated adult erythrocyte suspensions were subjected to low amplitude oscillatory shear in a Weissenberg rheogoniometer equipped with a cone-and-plate assembly. The dynamic viscoelastic properties of the suspension were measured over a broad range of frequency by a numerical solution that accounted for fluid inertia. Variation of shear amplitude and cell volume percent, and comparison of buffered saline, plasma, and dextran as suspending media showed that the cellular elements had undergone small bending and shearing deformations. Studies of normal adult erythrocytes, hypotonically swollen cells, temperature-altered cells, and erythrocyte ghosts suggested that the method was evaluating membrane material properties. The normal membrane was found to exhibit a shear rate dependent elastic modulus that increased by more than a factor of 20 over a frequency range from 0.0076 Hz to 60 Hz. The membrane viscosity showed a substantial drop with frequency indicative of a frequency thinning phenomenon. At high frequency of deformation the viscous response of normal erythrocytes was no longer indicative of a membrane property due to the dominant influence of the internal hemoglobin solution. The studies generally supported the ability of the method to quantify relative membrane material properties and detect changes in membrane structure. 相似文献
943.
944.
Total amplified DNA in methotrexate-resistant mouse lymphoma EL4 cells and mouse melanoma PG19 cells has been characterized in two ways. Metaphase spreads show the presence of additional chromosome forms that are either “homogeneously staining” chromosomes or “double minute” and ring chromosomes. Gel electrophoresis of restriction enzyme-digested nuclear DNA shows the presence of amplified sequences, the pattern of which is unique in each of five cell lines. We conclude that extensive DNA rearrangement has taken place during amplification. 相似文献
945.
Carp (Cyprinus carpio) hemoglobin readily autoxidizes in blood smears. Quantification of Soret-band absorbance in individual erythrocytes by means of scanning cytophotometry therefore requires more elaborate methods of preparation of blood samples. Of the fixatives that have been tested, suspension of whole blood in isotonic salt solutions containing glutaraldehyde was most suitable. Glutaraldehyde-fixed red blood cells are totally resistant to hemolysis. In the course of fixation, hemoglobin is transformed to methemoglobin. Spectrophotometry indicated extensive similarities between glutaraldehyde-fixed carp methemoglobin and human methemoglobin. In aqueous solutions, the intensity of the Soret-peak was pH-dependent. The allosteric modifier organic polyphosphate caused an R----T transition, resulting in increased molar extinctions. Dried preparations showed Soret-spectra that were not influenced from either pH or organic polyphosphate concentration of the aqueous suspensions in which the erythrocytes had been stored. The same was true for slide preparations of cyanomethemoglobin, easily derived from methemoglobin on addition of potassium cyanide. In the absence of oxygen fresh blood cells from carp slowly transform their hemoglobin into deoxyhemoglobin. Spectra of the intermediate stages of deoxygenation, Hb4(O2)3, Hb4(O2)2 and Hb4(O2), as well as mixtures of these intermediates, could be monitored. 相似文献
946.
Characterization of a transferrin-diphtheria toxin conjugate 总被引:3,自引:0,他引:3
We report here the synthesis and properties of a hybrid toxin prepared by covalently coupling diphtheria toxin to transferrin. The purified material contained two major hybrid protein species and was highly cytotoxic to mouse LMTK- cells in culture, reducing protein synthesis by 50% in 24 h at a concentration of 1 ng/ml. Cytotoxic activity was completely abolished in the presence of exogenous transferrin or anti-transferrin or anti-diphtheria toxin, thus demonstrating that the hybrid toxin was intoxicating cells via their transferrin receptors and that both the diphtheria toxin and transferrin components of the conjugate were necessary for activity. NH4Cl, a drug that elevates the pH within acidic intracellular vesicles, also blocked cytotoxic activity, suggesting that a low intravesicular pH was required for activity. The inhibitory effect of NH4Cl could be abolished by exposing toxin-treated cells to acidic culture medium, further implicating an acid-dependent step in the mechanism of the hybrid toxin action. Studies on the kinetics of intoxication also implied that endocytosis and exposure to a low pH within vesicles were necessary for cytotoxicity. Altogether, the results suggest that the transferrin-diphtheria toxin conjugate binds to transferrin receptors and is internalized into acidic endocytic vesicles. The enzymatic moiety of diphtheria toxin then apparently enters the cytosol in response to the low pH and subsequently arrests protein synthesis. 相似文献
947.
948.
A González-Fernández J Sans P Aller C de la Torre 《Cell biology international reports》1985,9(3):237-243
Bromosubstitution for most of the S period in synchronous populations of Allium cepa L. meristematic cells resulted in a delay in the late S-G2 transition point where protein synthesis is needed for later mitotic entrance to occur. This retardation in the position of the transition point was not accompanied by the expected delay in the entrance into mitosis, suggesting that such protein synthesis is a requisite, but not a timer for prophase triggering. 相似文献
949.
The survival of Salmonella typhimurium LT2 and Escherichia coli was studied in situ in a tropical rain forest watershed using membrane diffusion chambers. Numbers were determined by acridine orange staining and a Coulter counter. Population activity was determined by microautoradiography, cell respiration, frequency of dividing cells, and by nucleic acid composition. Numbers of Salm. typhimurium and E. coli decreased less than 1 log unit after 105 h as measured by direct count methods. Activity as measured by respiration, acridine orange activity, frequency of dividing cells, and microautoradiography indicated that both bacteria remained moderately active during the entire study. After 24 h, E. coli was more active than Salm. typhimurium , as measured by nucleic acid composition, and frequency of dividing cells. Both E. coli and Salm. typhimurium survived and remained active in this tropical rain forest watershed for more than 5 d, suggesting that Salm. typhimurium may be of prolonged public health significance once it is introduced into tropical surface waters. As E. coli was active and survived for a long time in this natural environment, it would seem to be unsuitable as an indicator of recent faecal contamination in tropical waters. 相似文献
950.
A selective system toxic towards mammalian cells expressing the liver-specific isozyme of alcohol dehydrogenase (L-ADH) has been developed. A number of alpha-unsaturated primary and secondary alcohols were assayed for their ability to serve as substrates for rat liver ADH and were screened for cytotoxicity towards L-ADH+ and L-ADH- cells. 1-Propen-3-ol and 1-penten-3-ol were identified as agents showing selective cytotoxicity. Reconstruction experiments demonstrated that 1-propen-3-ol at a concentration of 15 microM could be used to recover L-ADH- clones from mixed populations of L-ADH+ and L-ADH cells. Cells expressing the non-allelic S-ADH isozyme were not killed under these conditions. The selective system defined in this report is thus isozyme-specific. 相似文献