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941.
The chromosome-breaking activity of four 1-(phenyl)-3,3-dimethyltriazenes was tested in vitro on human peripheral blood lymphocytes using S9 mix as a metabolic activation system. 1-(4-Nitrophenyl)-3,3-dimethyltriazene was the most active compound. The difference in the frequency of chromosomal aberrations in a test with and without metabolic activation was significant at the 1% level of significance. The lowest frequency of chromosomal aberrations was induced by 1-(4-methylphenyl)-3,3-dimethyltriazene which, under the conditions of this experiment, is the least stable and probably rapidly degraded to non-active compounds. The chromosomal aberrations were also induced by 1-(4-chlorophenyl)-3,3-dimethyltriazene and 1-(4-bromophenyl)-3,3-dimethyltriazene, this activity was unrelated to metabolic activation. 相似文献
942.
The nucleoli of normally functioning guinea-pig hepatocytes that have a nucleolonemal (strand-like) organization differ from identical nucleoli of other cells. Their nucleolonema consists as a rule of a fibrillar component with 45S RNA and is poor in granulas that contain pre-rNA molecules of an intermediate size and 28S rRNA, a dense fibrillar component with nascent rRNPs in its composition was not revealed. In hepatocytes stimulated by a 2/3 liver resection rearrangements in nucleoli were found. This brought to a conclusion that rRNA metabolism undergoes some changes. In 2.5 and 5 hours after the resection the hepatocytes' nucleoli were characteristic of a greater thickness of strands and a smaller size of vacuoles, appearance of distinct zones of the dense fibrillar component and an increased amount of RNP-granules. All these observations taken together point out at an increased synthesis and processing of rRNA at early stages of the prereplicative period. In 9 hours the character of changes in nucleoli was different: the vacuoles were considerably widened, whereas the thickness of strands that consisted of a well-expressed dense fibrillar, fibrillar and granular components was lesser. Such rearrangement points out at an increased transport of preribosomes from the nucleolus, a high level of synthesis and processing of nascent RNP-product being maintained. The changes of nucleolar RNP-component were followed by appearance of greater blocks of perinucleolar condensed chromatin, which may be connected with "cutting-off" some tissue-specific genes and initiation of functioning of the mitotic operon genes. 相似文献
943.
Intrinsic protein fluorescence of native plant toxin and its isolated subunits were studied. The effect of pH was studied on: conformation of ricin and its A- and R-chains; affinity to galactose of ricin and its binding B-subunit. At two pH 5.0 and 7.0, the structural stability of toxin and subunits was estimated according to denaturational action of guanidine chloride. It was demonstrated that position of maximum and the spectrum shape of fluorescence of native toxin and catalytical A-subunit insignificantly depends on pH in the range of 3-8, whereas sufficient changes of the separameters for the ricin B-chain reveal structural transition at pH 4-5. The affinity of galactose of ricin and its isolated B-chain depends on pH, the maximal binding is observed at pH 7. The structural stability of ricin and isolated chains significantly differs at pH 7.5 and 5.0, thus the structure stability of ricin and A-chain increases, and that of B-chain decreases at pH 5.0. 相似文献
944.
A stable staining procedure of sister-chromatid differentiation (SCD) using a monoclonal antibromodeoxyuridine (BrdU) antibody was newly established by combining it with the immunoperoxidase reaction (3,3'-diaminobenzidine, DAB reaction). This procedure permitted detection of SCD and SCE at very low BrdU concentrations. SCD was not usually observed below 2.0 micrograms/ml BrdU with flame-dried chromosome slides. When chromosome slides were prepared by air-drying over 37 degrees C warm water, SCD was detected at 10.0, 5.0, 1.0, 0.5, 0.3 and 0.2 micrograms/ml BrdU with FPG and even at 0.1 microgram/ml BrdU with the antibody technique. SCE levels were evaluated using the antibody technique and endomitotic analysis with FPG at low BrdU concentrations (1.0, 0.5, 0.3, 0.2 microgram/ml) in two BS B-lymphoblastoid cell lines (LCLs). Even though the BS SCE level was approximately 70 per cell at 10 micrograms/ml, the value decreased to the level of 20-30 SCE per cell at 0.1 microgram/ml with the antibody technique. In BrdU-labelled BS endomitoses, single SCEs highly decreased with BrdU concentrations (130-140 level at 10 micrograms/ml: 38-60 level at 0.2 microgram/ml), when compared to the rare twin SCE values (3-6 SCE level) at all BrdU concentrations. These findings conclusively indicate that the spontaneous baseline SCE in BS B-lymphoblastoid cells is low and most BS SCEs are caused by BrdU. 相似文献
945.
Mutagenicity of N4-aminocytidine and its derivatives in Chinese hamster lung V79 cells. Incorporation of N4-aminocytosine into cellular DNA 总被引:2,自引:0,他引:2
N4-Aminocytidine induced mutation to 6-thioguanine resistance in Chinese hamster lung V79 cells in culture. Previous studies with experimental systems of in vitro DNA synthesis and of phage and bacterial mutagenesis have shown that this nucleoside analog induces base-pair transitions through its incorporation into DNA, with its erroneous base-pairing property. Incorporation of exogenously added [5-3H]N4-aminocytidine into the DNA of V79 cells was in fact observed in the present study. N4-Aminodeoxycytidine was not mutagenic for the V79 cells. Several alkylated N4-aminocytidine derivatives were tested for their mutagenicity in this system. Those with an alkyl group on the N'-nitrogen of the hydrazino group at position 4 of N4-aminocytidine were mutagenic, but those having an alkyl on the N4-nitrogen were not. These results are consistent with those previously observed in the bacterial mutagenesis systems, and agree with a mechanism of mutation in which a tautomerization of N4-aminocytosine is the necessary step for causing the erroneous base pairing. 相似文献
946.
Polar solvent extracts of tobacco snuff under acidic conditions were mutagenic in Salmonella typhimurium. Using the Griess reagent test, nitrite ranging from approximately 1.8 to 5.4 mg/g of snuff was found in the polar fraction of extracts. After acid treatment, nitroso compounds in the amount corresponding to the nitrite concentration were detected. The mutagenic potency of the acid-treated extracts was consistent with the content of nitroso compounds generated. Formation of nitroso compounds and the mutagenic activity under acidic conditions was inhibited by ascorbic acid. The results indicate that a nitrosation process was involved in snuff extracts during acid treatment. Studies related to the source of nitrite in tobacco snuff demonstrated that snuff contained bacteria which were able to reduce nitrate to nitrite and that the amount of nitrite in snuff extracts could be further increased by incubation of the extracts with the bacteria. Since snuff contains a considerable amount of nitrate, it seems that reduction of nitrate in snuff to nitrite by bacteria, and nitrosation of certain constituents in snuff by nitrite under acidic conditions to form mutagenic nitroso compounds are possible mechanisms responsible for the acid-mediated mutagenicity of snuff extracts. 相似文献
947.
Effect of bacterial growth-inhibiting ingredients on the Ames mutagenicity of medicinal herbs 总被引:1,自引:0,他引:1
A solvent fractionation method was introduced to screen for mutagenicity in 10 medicinal herbs being consumed in Korea. The Ames mutagenicity test result of Scutellariae and Rhei was significantly increased by eliminating growth-inhibiting substances through solvent fractionation of the crude extract. It is suggested that a physicochemical pretreatment should reduce the false-negative results which are caused by the presence of growth-inhibiting substances in complex mixtures. 相似文献
948.
949.
Energization and activation of inorganic carbon uptake by light in cyanobacteria 总被引:11,自引:3,他引:8
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The requirement of the inorganic carbon (Ci) transport system for light in cyanobacteria was investigated in Anabaena variabilis by the filtering centrifugation technique and in a mutant (E1) isolated from Anacystis nidulans using a gas exchange system. Ci transport capability increased with time of preillumination and decreased following darkening. Full activity could not be obtained by operating either photosystem II (PSII) or photosystem I alone. 3(3,4 Dichlorophenyl)-1,1 dimethylurea strongly inhibited Ci uptake. Very low activity of PSII was sufficient to activate Ci uptake. However, in the presence of dithiothreitol PSII activity was not required. We conclude that light may be required to activate as well as to energize Ci uptake in cyanobacteria. 相似文献
950.
Consequence of Absence of Nitrate Reductase Activity on Photosynthesis in Nicotiana plumbaginifolia Plants 总被引:6,自引:1,他引:5
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Saux C Lemoine Y Marion-Poll A Valadier MH Deng M Morot-Gaudry JF 《Plant physiology》1987,84(1):67-72
Chlorate-resistant Nicotiana plumbaginifolia (cv Viviani) mutants were found to be deficient in the nitrate reductase apoprotein (NR−nia). Because they could not grow with nitrate as sole nitrogen source, they were cultivated as graftings on wild-type Nicotiana tabacum plants. The grafts of mutant plants were chlorotic compared to the grafts of wild type. Mutant leaves did not accumulate nitrogen and nitrate but contained less malate and more glutamine than wild leaves. They exhibited a slight increase of the proportion of the light-harvesting chlorophyll a/b protein complexes and a lowering of the efficiency of energy transfer between these complexes and the active centers. After a 3 second 14CO2 pulse, the total 14C incorporation of the mutant leaves was approximately 20% of that of the control. The 14C was essentially recovered in ribulose bisphosphate in these plants. It was consistent with a decline of ribulose bisphosphate carboxylase activity observed in the mutant. After a 3 second 14CO2 pulse followed by a 60 second chase with normal CO2, 14C was mainly accumulated in starch which was labeled more in the mutant than in the wild type. These results confirm the observation that in the nitrate reductase deficient leaves, chloroplasts were loaded with large starch inclusions preceding disorganization of the photosynthetic apparatus. 相似文献