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51.
52.
The exposure of mouse splenic lymphocytes to the microtubule assembly-promoting drug taxol (10 microM for 4 h) results in an extensive reorganization of the microtubule system to form one to a few large bundles of microtubules, which extend from the centrosome. Lymphocytes pretreated with taxol for 4 h, or cultured in the continued presence of taxol, respond normally to the mitogen concanavalin A up to, and including, the stage of DNA replication. In contrast, the induction of DNA synthesis during the alloactivation of lymphocytes is inhibited when taxol is present in the mixed leukocyte culture. If the stimulators are pretreated with this drug, the mixed leukocyte reaction occurs normally, but pretreatment of the responders inhibits the proliferative response markedly. Microscopic observations of nuclear morphologies in these populations and autoradiography indicate that taxol inhibition occurs early in alloactivation, prior to DNA replication. The responding ability of taxol-treated lymphocytes is not restored to control levels by the addition of interleukin 2, leading to the suggestion that interleukin 2 receptors do not emerge or function normally in these cells. We conclude that the capacity to respond to allogeneic cells, but not to a mitogen, is dependent on the presence of the normal submembranous organization of the microtubule system. 相似文献
53.
Chronic treatment of hamsters with estradiol for several months has previously been shown to decrease the specific content
of cytochrome P450 in the kidney, a target of hormonal carcinogenesis, but not in liver. The reason for this decrease in metabolic
enzyme activity is unknown and has been examined in this investigation. We now report that the decrease in specific content
of renal cytochrome P450 by 73% in response to estradiol was not affected by co-treatment with tamoxifen for 1 month. The
subcutaneous infusion of 250 μg/day estradiol for 7 days lowered renal cytochrome P450 by 71% from control values and was
therefore used for further mechanistic studies. This treatment decreased renal activities of estradiol 2- or 4-hydroxylase
by 77 to 80%, of 7-ethoxycoumarin-O-deethylase by 66% of control values, respectively, and completely eliminated aryl hydrocarbon
hydroxylase activities, whereas liver enzymes remained unaffected. After 7 days of infusion of estradiol, fluorescent products
of lipid peroxidation were more than doubled in hamster kidney but remained unchanged in liver. The possibility of enzyme
destruction by binding of estradiol 2,3-quinone to metabolizing enzymes was investigatedin vitro. In the presence of 2-hydroxyestradiol, cumene hydroperoxide, and microsomes, conditions known to favor the oxidation of
the steroid to quinone, the binding of catechol estrogen metabolite to microsomal protein increased 60 fold over control values
in the absence of cofactor. Purified rat liver cytochrome P450c also oxidized 2-hydroxyestradiol to 2,3-estradiol quinone.
The rate of oxidation was linear for the first 2–3 min, but thereafter decreased with time. Under these incubation conditions,
irreversible binding of catechol estrogen metabolite to cytochrome P450c increased for the first 2–3 min and then remained
at this plateau level. It was concluded that enzyme destruction by a reactive estrogen metabolite or by lipid peroxides may
be a major reason for the organ-specific decrease in cytochrome P450 enzymes in kidneys of estrogen-treated hamsters. 相似文献
54.
Anaerobic growth on elemental sulfur using dissimilar iron reduction by autotrophic Thiobacillus ferrooxidans 总被引:2,自引:0,他引:2
Abstract Anaerobic growth on elemental sulfur using dissimilar iron reduction by Thiobacillus ferrooxidans has been demonstrated. The ferric ion reducing activity (FIR) of the anaerobic cells was double that of the aerobic cells. Significant differences in inhibition of FIR by respiratory inhibitors were observed between aerobic and anaerobic cells. A higher amount of cytochrome was detected in anaerobic cells compared to aerobic cells. Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium. The possibility of two different electron transport chains in ferric ion reduction is discussed. 相似文献
55.
Roy E. Crabtree Edward C. Cyr Renée E. Bishop Laura M Falkenstein John M. Dean 《Environmental Biology of Fishes》1992,35(4):361-370
Synopsis Leptocephali were collected in June 1981 and July 1989 over the continental shelf and slope of the Florida west coast. Tarpon larvae ranged 5.5–24.4 mm standard length (SL) and were the second most abundant leptocephalus species. Sagittae examined with compound microscopes and scanning electron microscopy had increments that were presumed to be formed daily. Increment counts made using the two microscopic techniques were not significantly different. Estimated ages ranged 2–25 days with a growth rate (± standard error) of 0.92 ± 0.04 mm d–1 The least squares linear regression equation SL = 2.78 + 0.92 (age in days) best described the relationship between estimated age and length. Adult tarpon appear to undergo a substantial spawning migration from inshore areas frequented during spring and summer to offshore spawning grounds. Spawning occurs during May, June, and July, although the spawning season may be of greater duration. 相似文献
56.
MNNG-induced killing of V79 cells has been found to be enhanced on inhibition of topoisomerase II activity by nalidixic acid and poly(ADP-ribose) polymerase synthesis by benzamide. Using these 2 inhibitors in conjunction after MNNG treatment, some overlap in the functions of these 2 enzymes was observed. Nalidixic acid and benzamide were found to suppress the yields of mutations and SCEs induced by MNNG. Benzamide was more effective in suppressing the mutation yield whereas nalidixic acid was more effective in suppressing SCEs. A model based on the relative requirement of topoisomerase and poly(ADP-ribose) for the repair of different types of damage has been proposed to explain the results. 相似文献
57.
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59.
Genetic manipulation of E-cadherin expression by epithelial tumor cells reveals an invasion suppressor role 总被引:118,自引:0,他引:118
A cDNA encoding the cell-cell adhesion molecule E-cadherin was transfected into highly invasive epithelial tumor cell lines of dog kidney or mouse mammary gland origin. Transfectants with a homogeneously high expression of E-cadherin showed a reproducible loss of activity in two types of in vitro invasion assays. Invasiveness of these transfectants could be reinduced specifically by treatment with anti-E-cadherin antibodies. In vivo, they formed partly differentiated tumors, instead of fully undifferentiated tumors. Alternatively, a plasmid encoding E-cadherin-specific anti-sense RNA was introduced into noninvasive ras-transformed cells with high endogenous E-cadherin expression. The resulting down-regulation, albeit partial, rendered the cells invasive. These data provide direct evidence that E-cadherin acts as an invasion suppressor molecule. 相似文献
60.