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171.
Arsenic compounds are known carcinogens. Although many carcinogens are also mutagens, we have previously shown that sodium
arsenite is not mutagenic at either the Na+/K+ ATPase orhprt locus in Chinese hamster V79 cells. It can, however, enhance UV-mutagenesis. We now confirm the nonmutagenicity of sodium
arsenite in line G12, a pSV2gpt-transformed V79 (hprt
−) cell line, which is able to detect multilocus deletions in addition to point mutations and small deletions. The lack of
arsenic mutagenicity has led to studies emphasizing its comutagenicity. Sodium arsenite at relatively nontoxic concentrations
(5 μM for 24 h or 10 μM for 3 h) is comutagenic withN-methyl-N-nitrosourea (MMU) at thehprt locus in V79 cells. Using a nick translation assay, which measures DNA strand breaks by incorporating radioactive deoxyribonucleoside
monophosphate at their 3′OH ends in permeabilized cells, we found that much more incorporation was seen in cells treated with
MNU (4 mM, 15 min) followed by 3-h incubation with 10 μM sodium arsenite compared with cells exposed to the same MNU treatment followed by 3-h incubation without sodium arsenite.
This result shows that in the presence of arsenite, strand breaks resulting from MNU or its repair accumulate over a 3-h period.
We suggest that the repair of MNU-induced DNA lesions may be inhibited by arsenite either by affecting the incorporation of
dNMPs into the MNU-damaged DNA template or by interfering with the ligation step. 相似文献
172.
Scavenging effect of extracts of green tea and natural antioxidants on active oxygen radicals 总被引:14,自引:0,他引:14
With the use of the spin trapping methods, the scavenging effects of the extracts of green tea and other natural foods are studied. In stimulated polymorphonuclear leukocytes (PMN) system, water extract fraction 6 (F6) from green tea and green tea polyphenols (GTP) have the strongest scavenging effect on the active oxygen radicals, much stronger than vitamin C (Vc) and vitamin E (VE). Rosemary antioxidants (RA) and Curcumin (Cur) have weaker scavenging effects than Vc, but stronger than VE. In Fenton Reaction, Cur has the strongest scavenging effect (69%) on hydroxyl radicals. In irradiation, riboflavin system F6(74%) and GTP(72%) have very strong scavenging effects that are weaker than Vc, but much stronger than VE (23%). With the use of spin probe oxymetry, the oxygen consumption in respiratory burst of stimulated PMN were measured when the antioxidants existed in these systems. The results demonstrated that these antioxidants did not affect the respiratory burst of human polymorphonuclear leukocytes stimulated with PMA. 相似文献
173.
174.
Err-Cheng Chan Peter Pear Ueng Li Fu Chen 《Applied microbiology and biotechnology》1989,31(5-6):524-528
Summary The Escherichia coli xylose isomerase gene was transformed into Schizosaccharomyces pombe for direct d-xylose utilization. In order to understand d-xylose metabolism and determine the limiting factors on d-xylose utilization by the transformed yeast, d-xylose transport, xylose isomerization, and xylulose phosphorylation were investigated. The results indicated that low activity of xylose isomerization in the cloned yeast was the limiting step for d-xylose fermentation. An in vitro study showed that yeast proteases decreased xylose isomerase activity. Xylitol, a by-product of d-xylose fermentation, had no effect on the activity of xylose isomerase. 相似文献
175.
K G Li N S Kobets V M Andrianov 《Molekuliarnaia genetika, mikrobiologiia i virusologiia》1989,(6):6-11
The 1.5 kb EcoRI--HindIII fragment of the pTiC58 containing the virD regulatory sequence demonstrates a constitutive promoter activity in E. coli background and an inducible one in agrobacterium. The virG gene was cloned in pTZ19R plasmid. To reveal the virG product--virD regulatory sequence interaction a few protein fractions of E. coli harbouring the obtained recombinant plasmid pTZ19G lysate were used. PAGE-retardation assay revealed the specific binding between the 1.5 kb DNA fragment containing 5'-end of virD and a separate protein fraction of the bacterial lysate. 相似文献
176.
仙茅属三个国产种的核型研究 总被引:1,自引:0,他引:1
本文报道了中国产三种仙茅植物的核型。1.绒叶仙茅Curculigo crassifolia (Baker) Hook. f., 2n=2x=18=10m(4SAT) 8 sm;2.大叶仙茅C.capitulata(Lour.)O. Kuntze,2n=2x=18=10(2SAT) 8sm;3.中华仙茅C.sinensis S.C.Chen,2n=2x=18=8m(3SAT) 10sm(2SAT)。其中中华仙茅的核型为首次报道。虽然三种仙茅的核型都是“2B”型,但中华仙茅的核型不对称性比绒叶仙茅和大叶仙茅强。 相似文献
177.
178.
Actinomycetes were isolated from the upper 1 - 3 cm of the soil layer in a well-developed forest and in an adjacent clearcut
area where Douglas-fir [Pseudotsuga menziesii (MIRB.) Franco] regeneration had been impaired for two decades. The population density in the clearcut area was two times
as high as that in the forested area. The percentage of actinomycetes that inhibited seed germination of the test plants was
significantly higher in isolates obtained from the clearcut area than in those obtained from the forested area, and isolates
from the clearcut showed five times the phytotoxic effect of those from the forest. Some actinomycete isolates, 4 % from the
clearcut and 2.6 % from the forest, significantly reduced in vitro growth of two common ectomycorrhizal fungi of Douglas-fir,Laccaria laccata andHebeloma ovstuliniforme. Two actinomycete isolates from the clearcut reduced fungal growth by 40 % and 73 %. Reduction of the nutrient in the growth
medium did not affect the antifungal activity of the actinomycetes. The data support the idea that, along with other factors,
phytotoxic and antifungal actinomycetes may suppress natural regeneration or establishment of planted seedlings - either directly
or. indirectly - through inhibition of seed germination or of mycorrhizal fungi. 相似文献
179.
Recently, patch-clamping of yeast protoplasts has revealed the presence of plasma membrane K+ channels (Gustin, M. C., B. Martinac, Y. Saimi, M. R. Culberston, and C. Kung. 1986. Science (Wash. DC). 233:1195-1197). In this work we show that fusion of purified plasma membranes into planar bilayers allows the study of the yeast channels. The main cationic conductances detected were of 64 and 116 pS, however, larger and smaller conductances have been observed. The two main conductances were sensitive to the K+ channels blockers tetraethylammonium (TEA+) and Ba2+. Bionic experiments indicated that both conductances were K+ selective. 相似文献
180.
Male mice castrated on day 0 after birth were pretreated daily with testosterone propionate (TP, 4 micrograms/g body weight), 17 beta-estradiol (E2, 0.2 micrograms/g body weight) or vehicle for 21 days starting from day 20. In another experiment, male mice were castrated on day 25; two pituitaries from 60-day-old females were immediately grafted under the capsule of the left kidney in one group. The castrated mice with or without grafts were pretreated daily with TP (4 or 20 micrograms/g body weight) for 36 days starting from day 25, and the left kidney was removed on day 60. Daily TP injections (4 micrograms/g body weight) were started again at 30 days after the end of pretreatments to examine androgen-induced proliferation, and incorporation of 5-[125I]iodo-2'-deoxyuridine into the whole seminal vesicles was used as an index of proliferation. In the neonatally castrated mice, both TP and E2 pretreatments given during the prepubertal period significantly increased seminal vesicle weight even long after the end of the pretreatments. However, androgen-induced proliferative response found in the neonatally castrated adult mice (poor response; long duration with a low peak) was changed to that found in mice castrated at adulthood (good response; short duration with a high peak) by the TP pretreatment only but not at all by the E2 pretreatment. In the mice castrated on day 25, a pharmacological dose of TP or TP plus hyperprolactin could not enhance or change the adult castration type of androgen-induced proliferation induced by physiological prepubertal androgens, although both treatments significantly enhanced the prepubertal growth of the seminal vesicles. 相似文献