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911.
D Ayusawa K Iwata T Kozu S Ikegami T Seno 《Biochemical and biophysical research communications》1979,91(3):946-954
Mutants that were resistant to aphidicolin were isolated from mutagenized mouse FM3A cells at a frequency of about 10?6. Resistance to aphidicolin in these mutants was not due to an effect on [3H]thymidine incorporation into DNA, DNA synthesis in permeabilized cells, or DNA polymerase α.All the mutants showed a greatly increased dATP pool and decreased ability to incorporate [3H]deoxycytidine into DNA. They also showed cross-resistance to both 1-β-D-arabinofuranosyladenine and 1-β-D-arabinofuranosylcytosine.These results indicate that an enzyme involved in production of dATP or its regulation is altered in these mutants. It is suggested that dATP competes with aphidocolin at its killing site or that dATP reverses the effect of aphidicolin by some unknown mechanism . 相似文献
912.
M Yamada M Tsuda M Nagao M Mori T Sugimura 《Biochemical and biophysical research communications》1979,90(3):769-776
Mutagenic compounds isolated from pyrolysates of tryptophan, glutamic acid and globulin were broken down by myeloperoxidase and hydrogen peroxide with loss of their mutagenicity toward Salmonella typhimurium TA98. Lactoperoxidase and horseradish peroxidase were as effective as myeloperoxidase in degradation of the mutagens. 相似文献
913.
When incubated at 37 °C in medium containing antibodies specific for thymus-leukemia (TL) antigens, viable cells bearing these antigens become resistant to the cytolytic effects of guinea pig complement, a process termed antigenic modulation. Antibody-induced membrane redistribution of the TL antigens, detected by indirect immunofluorescence, occurs with a similar pace. When high concentrations of concanavalin A (Con A) were included with antibodies in the incubation medium, TL antigenic modulation as well as antigen patching and capping were markedly inhibited, similar to effects of Con A on membrane immunoglobulin redistribution with murine spleen cells. Colchicine antagonized the inhibition by Con A suggesting the involvement of microtubules. In parallel experiments high concentrations of Con A failed to alter the quantity of TL antigen expression or its rate of change with time during incubation in cognate antisera. These results support the hypotheses that (a) generalized alterations in membrane receptor mobility may be induced by ligand binding to the cell membrane, and (b) under certain conditions stable interactions occur between normally independent cell surface antigens. 相似文献
914.
Spermatozoa of the American oyster Crassostrea virginica were frozen to ?196 °C in concentrated Hanks' salt solution (2.6×) containing 8% dimethyl sulfoxide. About 0.2 ml of spermatozoa that were stored in liquid nitrogen for 68 days fertilized 91% of 65,600 eggs compared to fresh spermatozoa, which fertilized 92% of approximately the same number of eggs from the same females. Larvae resulting from fertilization of fresh eggs with 39-day-old cryopreserved spermatozoa appeared normal after 11 days. 相似文献
915.
916.
917.
A procedure is described that enables use of the p-phenylphenol color reaction to determine acetaldehyde in the presence of formaldehyde. The sample is first treated with an acidic 2,4-pentanedione reagent, which selectively removes formaldehyde. The method is applicable to blochemical reactions using tissue preparations. 相似文献
918.
The conformations of the major coat protein of a filamentous bacteriophage can be described by nuclear magnetic resonance spectroscopy of the protein and the virus. The NMR experiments involve detection of the 13C and 1H nuclei of the coat protein. Both the 13C and 1H nuclear magnetic resonance (NMR) spectra show that regions of the polypeptide chain have substantially more motion than a typical globular protein. The fd coat protein was purified by gel chromatography of the SDS solubilized virus. Natural abundance 13C NMR spectra at 38 MHz resolve all of the nonprotonated aromatic carbons from the three phenylalanines, two tyrosines, and one tryptophan of the coat protein. The α carbons of the coat protein show at least two different classes of relaxation behavior, indicative of substantial variation in the motion of the backbone carbons in contrast to the rigidity of the α carbons of globular proteins. The 1H spectrum at 360 MHz shows all of the aromatic carbons and many of the amide protons. Titration of a 1H spectra gives the pKas for the tyrosines. 相似文献
919.
The pharmacological effects of PGE1 (6 and 9 days, 21,250 μg/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE1 hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE1 clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth >dentin formation >incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE1, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE1 lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE1 may induce a calcitonin-like action, a part of which may dependent on the calcinonin secretion is suggested. 相似文献
920.
Warren I. Schaeffer A. H. L. Chuang Nicholas Heintz Edward Bresnick 《In vitro cellular & developmental biology. Plant》1979,15(6):437-440
Summary We have tested the sensitivity of a cloned rat hepatocyte line, RL-PR-C, to aflatoxin B1 and benzo(a)pyrene as a function of population-doubling level. The cells were much more sensitive to the cytotoxic action
of these agents subsequent to 230 population doublings. This sensitivity corresponded to the enhanced inducibility of arylhydrocarbon
hydroxylase activity by 3-methylcholanthrene.
Supported by Grants CA 21258 and CA 12056 from the National Cancer Institute. 相似文献