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31.
Tungstate, a molybdate analog inactivating nitrate reductase, deregulates the expression of the nitrate reductase structural gene 总被引:19,自引:1,他引:18
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Nitrate reductase (NR, EC 1.6.6.1) from higher plants is a homodimeric enzyme carrying a molybdenum cofactor at the catalytic site. Tungsten can be substituted for molybdenum in the cofactor structure, resulting in an inactive enzyme. When nitratefed Nicotiana tabacum plants were grown on a nutrient solution in which tungstate was substituted for molybdate, NR activity in the leaves decreased to a very low level within 24 hours while NR protein accumulated progressively to a level severalfold higher than the control after 6 days. NR mRNA level in molybdate-grown plants exhibited a considerable day-night fluctuation. However, when plants were treated with tungstate, NR mRNA level remained very high. NR activity and protein increased over a 24-hour period when nitrate was added back to N-starved molybdate-grown plants. NR mRNA level increased markedly during the first 2 hours and then decreased. In the presence of tungstate, however, the induction of NR activity by nitrate was totally abolished while high levels of NR protein and mRNA were both induced, and the high level of NR mRNA was maintained over a 10-hour period. These results suggest that the substitution of tungsten for molybdenum in NR complex leads to an overexpression of the NR structural gene. Possible mechanisms involved in this deregulation are discussed. 相似文献
32.
Classical Raman spectroscopic studies of NADH and NAD+ bound to lactate dehydrogenase by difference techniques 总被引:2,自引:0,他引:2
The binding of the coenzymes NAD+ and NADH to lactate dehydrogenase causes significant changes in the Raman spectra of both of these molecules relative to spectra obtained in the absence of enzyme. The molecular motions of the bound adenine moiety of both NAD+ and NADH as well as adenine containing analogues of these coenzymes produce Raman bands that are essentially identical, suggesting that the binding of adenine to the enzyme is the same regardless of the nicotinamide head-group nature. We also have observed that the molecular motions of the bound adenine moiety are different from both those obtained when it is in either water, various hydrophobic solvents, or various other solvent compositions. Protonation of the bound adenine ring at the 3-position is offered as a possible explanation. Significant shifts are observed in both the stretching frequency of the carboxamide carbonyl of NAD+ and the rocking motion of the carboxamide NH2 group of NADH. These shifts are probably caused by hydrogen bonding with the enzyme. The interaction energies of these hydrogen-bonding patterns are discussed. The aromatic nature of the nicotinamide moiety of NAD+ appears to be unchanged upon binding. Pronounced changes in the Raman spectrum of the nicotinamide moiety of NADH are observed upon binding; some of these changes are understood and discussed. Finally, these results are compared to analogous results that were recently reported for liver alcohol dehydrogenase [Chen et al. (1987) Biochemistry 26, 4776-4784]. In general, the coenzyme binding properties are found to be quite similar, but not identical, for the two enzymes. 相似文献
33.
In v-mos transformed cells, glucocorticoid receptor (GR) proteins that bind hormone agonist are not efficiently retained within nuclei and redistribute to the cytoplasmic compartment. These cytoplasmic desensitized receptors cannot be reutilized and may represent trapped intermediates derived from GR recycling. We have used the glucocorticoid antagonist RU486 to examine whether v-mos effects can be exerted on any ligand-bound GR. In the rat 6m2 cell line that expresses a temperature-sensitive p85gag-mos oncoprotein, RU486 is a complete antagonist and suppresses dexamethasone induction of metallothionein-1 mRNA at equimolar concentrations. Using indirect immunofluorescence, we observe efficient nuclear translocation of GR in response to RU486 treatment in either the presence or absence of v-mos oncoproteins. However, in contrast to the redistribution of agonist-bound nuclear receptors to the cytoplasm of v-mos-transformed cells, RU486-bound GRs are efficiently retained within nuclei. Interestingly, withdrawal of RU486 does not lead to efficient depletion of nuclear GR in either nontransformed or v-mos transformed cells. It is only after the addition of hormone agonist to RU486 withdrawn v-mos-transformed cells that GRs are depleted from nuclei and subsequently redistributed to the cytoplasm. Thus, only nuclear GRs that are agonist-bound and capable of modulating gene activity can be subsequently processed and recycled into the cytoplasm. 相似文献
34.
祁慧霖 《分子细胞生物学报》1988,(1)
本文利用间接免疫荧光手段对间期核微管组织中心的性质进行了初步探讨。当分离核与6S微管蛋白保温后,用抗管蛋白抗体进行间接免疫荧光染色,在群体中只有极少数核上有微管生长。Triton X-100或溶血卵磷脂去膜核的实验证实能长微管的核是核膜缺失或破损核。用秋水仙素解聚核上长出的微管,可见核内荧光亮点数多于染色体数,说明核内微管组织中心数目多于着丝粒数,很可能包括着丝粒和一部分染色质颗粒。将秋水仙素和6S微管蛋白混合后与去膜核保温,结果6S微管蛋白与核内微管组织中心有亲和力。本文就这些结果进行了讨论。 相似文献
35.
36.
测定了3T3细胞、人和大鼠一些组织中DNA拓扑异构酶Ⅰ的活性;估计了核酸内切酶对拓扑酶Ⅰ松弛活性测定的干扰程度;发现增殖组织全细胞抽提液中酶比活高于正常分化组织,而且在异常增殖组织中酶比活的增高更为显著。 相似文献
37.
High-fidelity gene targeting in embryonic stem cells by using sequence replacement vectors. 总被引:22,自引:8,他引:14
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Mutations were targeted to the Hprt locus in murine embryonic stem cells by using sequence replacement vectors. When the vector was designed such that the mutated sequences were flanked on both sides by several kilobases of DNA homologous to the target locus, replacement of chromosomal sequences with the exogenous DNA occurred with precision. If, on the other hand, the target-homologous DNA on one arm of the vector was reduced to below 1 kb in length, the fidelity of recombination was diminished. 相似文献
38.
血管内皮舒张因子在氧自由基所致慢性缺氧大鼠肺内动... 总被引:1,自引:1,他引:0
The role of endothelium-derived relaxing factor (EDRF) on the effect of oxygen-derived free radicals (generated by xanthine-xanthine oxidase system) on intrapulmonary arterial in chronic hypoxic rats was studied by a microbioassay method. Intrapulmonary artery rings with intact or denuded endothelium of hypoxic (5,000 m, 10 days) and normoxic rats were prepared for observation of oxygen-derived free radicals induced contraction. It was shown that oxygen-derived free radicals induced contractions of intrapulmonary arterial rings with intact endothelium were obviously augmented in hypoxic rats than in normoxic controls. The augmented responses could be further potentiated by the addition of EDRF inactivator reduced hemoglobin (RHb), but diminished or even abolished by applying superoxide dismutase (Cu-Zn SOD). However, no effect on denuded rings was observed when RHb or SOD was added. It is concluded that chronic hypoxia may attenuate the action of EDRF in the enhancement of the reactivity of intrapulmonary artery to oxygen-derived free radicals. 相似文献
39.
Female Wistar rats were trained in a Skinner-box, 30 trials per day in a dark room to establish operant defence conditioning. Training started with a light (15 s), then combined with footshock for further 8 s. When the rats learned to press the key to avoid footshock within 15 s, conditioned response was considered established. After the rats reached a conditioning rate (CR) above 80% for 5 days, cannulae were implanted into caudate-putamen. Two to three days later, Met-enkephalin (MEK) or bestatin (an aminopeptidase inhibitor) was injected bilaterally into caudate-putamen. 30 min, 2 h, 24 h and 48 h after injection, conditioning tests were conducted, with each session consisting of 30 trials. Control experiments were done when 0.9% NaCl (NS) was injected. After injection of NS, CR maintained above 80% in all 4 test sessions. MEK (60 ng/rat) or bestatin (10 micrograms/rat) significantly lowered the CR during the 30 min and 2 h test session. In the latter case, the latency (L) was also prolonged. However both CR and L returned to the control level in the 24 h and 48 h test sessions. Naloxone (2 mg/kg, i.p.) blocked the conditioning-depression effect of bestatin. No significant alteration was seen in locomotor activity after MEK or bestatin injection. The results suggest that enkephalin in caudate-putamen may be involved in the regulation of retrieval of conditioning. Bestatin mimics the effect of MEK on conditioning reflex probably by increasing production of endogenous enkephalin. 相似文献
40.
Renmei Ren Kanhui Yan Yanjie Su Hanjun Qi Bin Liang Wunyong Bao Frans B. M. de Waal 《Primates; journal of primatology》1991,32(3):321-327
Observations were made following 130 spontaneous aggressive incidents in two small breeding groups of captive golden monkeys
(Rhinopithecus roxellanae roxellanae). Participants were observed both during the first 10 min following these incidents and during matched control observations.
An increased contact rate was observed between opponents following the aggressive incident. Post-conflict contacts were characterized
by a number of behavior patterns: open mouth, rapid grooming, embrace, and crouching. Adult males played an important role
as mediator in agonistic disputes among females: males intervened in 93.6% of female fights. It is speculated that this intervention
behavior is related to the species' organization into one-male units. 相似文献