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51.
Isolation and expression of three gibberellin 20-oxidase cDNA clones from Arabidopsis. 总被引:25,自引:8,他引:17 下载免费PDF全文
A L Phillips D A Ward S Uknes N E Appleford T Lange A K Huttly P Gaskin J E Graebe P Hedden 《Plant physiology》1995,108(3):1049-1057
52.
Theodor Günther Jürgen Vormann Vera Höllriegl 《Molecular and cellular biochemistry》1995,144(2):141-145
In primary cultures of rat hepatocytes, the effects of extracellular Mg2+ and Fe on lipid peroxidation (LPO) as measured by means of malondialdehyde (MDA) formation were investigated.Incubation of hepatocytes at decreasing extracellular Mg2+ concentration enhanced LPO, depending on extracellular Fe. About 96% of MDA accumulated in the culture medium. Addition of desferrioxamine prevented LPO.Additionally, the formation of oxygen free radicals was determined by fluorescence reduction of cis-parinaric acid. With this method, an immediate decay of fluorescence was found after addition of Fe2+. Fluorescence reduction was completely prevented by desferrioxamine, indicating the function of extracellular Fe. This mechanism may operate additionally to the increase in intracellular Fe and intracellular formation of oxygen free radicals during Mg deficiencyin vivo. 相似文献
53.
Mutational analysis of the RecA protein L1 region identifies this area as a probable part of the co-protease substrate binding site 总被引:3,自引:0,他引:3
Horacio G. Nastri Angelina Guzzo Craig S. Lange Graham C. Walker & Kendall L. Knight 《Molecular microbiology》1997,25(5):967-978
Previous mutational analysis of the L1 region of the RecA protein suggested that Gly-157 and Glu-158 are 'hot-spots' for the occurrence of constitutive LexA co-protease mutants (coprtc ). In the present study, we clearly establish that position 157 is a hot-spot for the occurrence of such mutants, as 12 of 14 and 10 of 14 substitutions result in this phenotype for UmuD and LexA cleavage respectively. The frequency of such mutations at position 158 is somewhat lower, 8 of 13 and 5 of 13 for UmuD and LexA respectively. Comparison of the UmuD vs. LexA co-protease activity for all single mutants with substitutions at positions 154, 155, 156, 157 and 158 (47 in total) reveals that, although there is good agreement among most mutants regarding their ability to cleave both LexA and UmuD, there are two in particular (Glu-154→Asp and Glu-154→Gln) that show a clear preference for cleavage of UmuD. We also show that three second-site mutations that completely suppress coprtc activity toward LexA have little or no effect on the coprtc activity of the primary mutant toward UmuD. In addition, we observe a high frequency of second-site suppressor mutations, suggesting a functional interaction among side-chains in this region. Together, these results support the idea that the L1 region of RecA makes up part of the co-protease substrate-binding site. 相似文献
54.
I. Szumiel M. Kapiszewska M. Kruszewski T. Iwaneńko C. S. Lange 《Radiation and environmental biophysics》1995,34(2):113-119
Cells from the L5178Y murine lymphoma subline LY-R are twice as resistent to killing by ionizing radiation than the subline LY-S. In contrast, LY-R cells are more sensitive to killing by H2O2, the effect being more pronounced at 37 °C than 0 °C. Initial DNA damage after H2O2 treatment (both temperatures, 5 min) has been estimated by the comet assay (single-cell gel electrophoresis) and fluorescent halo technique. According to both methods, the initial damage is significantly higher in LY-R cells, particularly that inflicted at O °C. Differences between DNA unwinding and rewinding abilities at pH 9 and 6.9 (estimated by the fluorescent halo technique) point to a considerable difference in pH-9-labile damage between the sublines, as observed previously for x-irradiated cells (Kapiszewska et al. 1992). In contrast to findings with x-irradiated cells, however, after H2O2 treatment this damage is more extensive in LY-R cells than in LY-S cells. Thus, the initial pH-9-labile damage corresponds to the pattern of sensitivity to H2O2 and x-rays. We suggest that this is caused by different proportions of cuprous and ferric ions found in the nuclei of LY sublines and by the different ability of these ions to react with H2O2 and water radiolysis products. The copper/iron ratio in the nucleus is 1.31 in LY-R cells and 4.84 in LY-S cells. 相似文献
55.
The paper explains how the formulas for calculating the surface area of the prolate spheroid, which a nucleus resembles, can be changed by suitable substitutions into formulas based on measured diameters l and k [mm] of the nucleus approach side surface, magnified 3.000 times, and on a mixed cyclometric function dependent on the axial ratio. Their values established for distinct axial ratios are compiled in a table. The values of the mixed cyclometric function are to be calculated for any other axial ratio according to a formula based on linear interpolation. The nucleus surface Omu is obtained in the natural order of magnitude [micron2]. In case of constant axial ratio, the surface area values form a second-order arithmetic progression, and a recursion formula has been developed to check the values of its terms. In case of nuclei of spherical shape or constant small diameter k, the surface area formulas may be simplified. Numeral examples serve for explanation. For all measured-value combinations involved, a second part, which is being prepared, will contain a complete table of function values, which is referred to in the Appendix and from which the values of the natural surface areas of spheroid nuclei can be gathered. 相似文献
56.
In 1974, Zimm described a theory which predicts that the sedimentation coefficient of high-molecular-weight DNA will decrease as the rotor speed of measurement increases. In 1979, this theory was revised, and the new formula predicts speed-dependence effects that are substantially smaller than the predictions of the original version. This report describes the results of subjecting both the original and the revised versions of the theory to quantitative tests using a well-defined sucrose-gradient system and a DNA of known molecular weight (T4c DNA). T4c bacteriophage is a mutant, whose DNA contains the unmodified base cytosine, instead of the glucosylated hydroxymethylcytosine characteristic of the T-even bacteriophages, and has a molecular weight of 115 ± 3 × 106. The DNA of the wild-type phage (T4D+) was also used in some experiments. In addition to the quantitative tests, the experiments test for an effect first observed by Rubenstein and Leighton, which showed that the sedimentation coefficient measured for T2 DNA depended on the composition of the centrifuge tube used for the measurement (tube composition effect). It can be inferred from this observation that an interaction occurs between particle and tube wall during sedimentation, and this leads to a reduction in sedimentation velocity independent of the reduction in S described by Zimm's theory. The results show that in the range of 25,000–50,000 rpm, the original but theoretically incorrect form of the theory quite accurately describes the sedimentation behavior of both T4c and T4D+ DNA, although T4D+ was a special case in some respects. The revised (corrected) form of the theory predicts much less of a speed-dependence effect than that actually observed. The discrepancy between corrected theory and observation suggests that other factors (perhaps arising from the use of the swinging bucket rotor geometry) are causing the additional observed reduction in S20,w. However, the experiments show that the tube composition effect does not seem to be one of these. 相似文献
57.
Summary Previous publications have reported on investigations of CO2 exchange in the desert lichenRamalina maciformis both in its natural habitat in the Negev and in the laboratory. Utilizing laboratory data, net photosynthesis and dark respiration were expressed as mathematical functions of the most important environmental factors. Based on these relationships, a model is developed that allows one to predict CO2 exchange of the plant. Input data are light intensity, temperature, and water content of the thallus, together with a measure of the rate of the seasonal change of photosynthetic and respiratory activity. The validity of the model is tested by comparing simulated daily courses of CO2 uptake and release of the lichen with independent results of CO2 exchange measurements conducted in the field during and after the condensation of dew. The sensitivity of the model is shown by simulating changes in the input data of temperature and water content of the lichen.This paper is dedicated to Dr. h.c. Oscar Klement on the occasion of his 80th birthday 相似文献
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60.
The effects of various pharmacological agents on neurally evoked contractions of the visceral muscles of the oviduct of Locusta migratoria have been examined. The pentapeptide, proctolin, at low concentrations (10?11 M?10?10 M), induced an increase in the amplitude of neurally evoked contractions and basal tonus, and induced the appearance and increased the frequency of myogenic contractions. Glutamate, at 10?4 M, produced a small transient contraction which in some preparations was accompanied by a reduction in amplitude of neurally evoked contractions. Octopamine, at 10?6 M, reduced the amplitude of neurally evoked contractions and also resulted in a relaxation of the muscles. The octopaminergic effects were inhibited by the α-aminergic antagonist phentolamine. Neurally evoked contractions were unaffected by dopamine, 5-HT or the acetylcholine receptor antagonists atropine and hexamethonium. Acetylcholine increased the amplitude of neurally evoked contractions, but only at the high concentration of 10?3 M. The possible role of proctolin and glutamate as excitatory neuro-transmitters and the inhibitory action of octopamine is discussed. 相似文献