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111.
112.
罗汉果双受精过程的细胞学观察 总被引:3,自引:1,他引:2
罗汉果(Siraitiagrosvenori(Swingle)C.Jemey)双受精过程属有丝分裂前配子融合类型,授粉后24~48h,花粉管进入胚囊,穿过一个助细胞,放出两个精子。雌雄核融合和雄核与次生核融合同时发生在授粉后62~72,雄核与次生核融合速度快于配子融合,72h后即可见到初生胚乳核分裂。合子中的雌雄核仁在授粉后第5~6d融合,授粉后8~9d合成分裂形成二细胞胚。在双受精过程中,多次观察到有多条花粉管进入胚囊和多精入极核现象。原胚期有附加花粉管从珠孔进入。 相似文献
113.
综述了近年来有关利用基因转移技术修饰肿瘤细胞制备肿瘤基因工程疫苗的最新研究进展,着重阐述了逆转录病毒载体介导的基因转移及其安全性;归纳了目前可用于肿瘤基因工程疫苗的各种目的基因的特点及作用并对这类肿瘤疫苗制备过程中所存在的问题进行了分析. 相似文献
114.
蛋白质特异性断裂试剂是近年来发展起来的一些具有特异性断裂肽键功能的化学工具.这些断裂试剂可分为两类,一类通过氧化断裂机制实现蛋白空间结构特异性切割,另一类通过水解断裂机制实现序列特异性切割.蛋白质特异性断裂试剂在蛋白质序列测定,蛋白质的结构与功能研究,蛋白质与核酸相互作用研究以及新型化学治疗药物的合成等方面有着广阔的应用前景. 相似文献
116.
溶剂极性及盐酸胍对碳酸酐酶构象的影响 总被引:1,自引:0,他引:1
以紫外荧光光谱为检测手段,比较研究了溶剂极性及盐酸胍对碳酸酐酶构象的影响,结果表明,当盐酸胍浓度小于1mol/L时酶呈天然构象,1.5mol/L-2.0mol/L的盐酸胍导致该酶呈伸展构象;而乙醇不以导致该酶产生稳定的中间态构象,1mol/L和3mol/L的甲醇以及3mol/L的乙醇对盐酸胍致碳酸酐酶中间态的影响不大,甲醇略使致中间态的盐酸胍浓度下降,乙醇略使之上升。 相似文献
117.
F.M.A.H. Schuurmans Stekhoven H.G.P. Swarts Y.-F. Fu G.A.J. Kuijpers J.J.H.H.M. de Pont S.L. Bonting 《生物化学与生物物理学报:生物膜》1984,774(2):277-287
(1) Treatment of from rabbit kidney outer medulla with the labeled thio-analogue of ATP in the presence of and the absence of K+ leads to thiophosphorylation of the enzyme. The value for [γ-S]ATP is 2.2 μM and for Na+ 4.2 mM at 22°C. Thiophosphorylation is a sigmoidal function of the Na+ concentration, yielding a Hill coefficient . (2) The thio-analogue () can also support overall activity, but at 37°C is only h?1 or 0.09% of the specific activity for ATP (). (3) The thiophosphoenzyme intermediate, like the natural phosphoenzyme, is sensitive to hydroxylamine, indicating that it also is an acylphosphate. However, the thiophosphoenzyme, unlike the phosphoenzyme, is acid labile at temperatures as low as 0°C. The acid-denatured thiophosphoenzyme has optimal stability at pH 5–6. (4) The thiophosphorylation capacity of the enzyme is equal to its phosphorylation capacity, indicating the same number of sites. Phosphorylation by ATP excludes thiophosphorylation, suggesting that the two substrates compete for the same phosphorylation site. (5) The (apparent) rate constants of thiophosphorylation (0.4 s?1 vs. 180 s?1), spontaneous dethiophosphorylation (0.04 s?1 vs. 0.5 s?1) and K+-stimulated dethiophosphorylation (0.54 s?1 vs. 230 s?1) are much lower than those for the corresponding reactions based on ATP. (6) In contrast to the phosphoenzyme, the thiophosphoenzyme is ADP-sensitive (with an apparent rate constant in ADP-induced dethiophosphorylation of 0.35 s?1, ) and is relatively K+-insensitve. The for K+ in dethiophosphorylation is 0.9 mM and in dephosphorylation 0.09 mM. The thiophosphoenzyme appears to be for 75–90% in the ADP-sensitive E1-conformation. 相似文献
118.
7-Methylbenz[a]anthracene (7-MBA) was metabolized stereoselectively by rat liver microsomes to form five optically active dihydrodiols as the predominant metabolites. The dihydrodiols were purified by a combination of reversed-phase and normal-phase high performance liquid chromatography (HPLC). By comparison of their circular dichroism (CD) spectra with the corresponding benz[a]anthracene (BA) dihydrodiols of known absolute stereochemistry, the major dihydrodiol enantiomers of 7-MBA have been determined to have 1R,2R-, 3R,4R- and 10R , 11R - absolute configurations, respectively. Due to their quasi- diaxial conformations, the absolute configuration of trans-5,6- and trans-8,9-dihydrodiols, the two most abundant metabolites of 7-MBA, could not be determined by simple comparisons of their circular dichroism spectra with those of the quasidi -equatorial BA 5R, 6R - and 8R , 9R -dihydrodiols. The major enantiomers of the quasi- diaxial trans-5,6- and trans-8,9-dihydrodiol metabolites of 7-MBA were determined by comparison to the CD spectrum of 7-bromo-BA 5R, 6R -dihydrodiol and by the exciton chirality method to have R,R absolute stereochemistry. This study also revealed that the circular dichroism Cotton effects of an enantiomeric dihydrodiol of polycyclic aromatic hydrocarbons can be drastically altered if the conformation (quasi- diaxial vs. quasi di-equatorial ) of the dihydrodiol is changed. 相似文献
119.
S S Matsuyama F S Yen L F Jarvik R S Sparkes T K Fu H Fisher N Reccius I M Frank 《Mutation research》1977,48(2):255-265
Sequential chromosome examinations of peripheral lymphocte cultures were carried out on 21 adult male volunteers who smoked natural blend marijuana cigarettes containing about 1%, 2%, or no delta9-THC. For a limited number of subjects, blood samples from a single venipuncture were cultured independently in two cytogenetic laboratories, and later the slides were exchaged for re-analysis. There were significant differences between laboratories in the absolute break frequencies recorded. These inter-laboratory differences were demonstrated for both techniques of cell culture and metaphase analysis. Neither laboratory found a statistically significant increase in break frequencies asssociated with marijuana smoking. The present study, therefore, failed to detect a measurable effect of marijuana smoking on chromosomal aberrations in subjects experienced in the use of the drug. 相似文献
120.
Chin Y. Yeh Peter P. Fu Frederick A. Beland Ronald G. Harvey 《Bioorganic chemistry》1978,7(4):497-506
molecular orbital theoretical calculations performed on the anti and syn diolepoxides (1 and 2) of the potent carcinogen benzo[a]pyrene provide insight into the molecular structure and reactivity of these mutagenic and carcinogenic hydrocarbon metabolites. Hydrogen-bonded interaction between the 7-HO proton and the epoxide oxygen atom of 2 is shown to be absent in the normal semichair conformation of the tetrahydro ring, (H…O bond distance = 2.7 Å), but is energetically favored in a somewhat distorted puckered structure (H…O bond distance = 1.7 Å). Unexpectedly, internal H-bonding alters the relative electron density at C9 and C10, leading to prediction of the former as the more electrophilic center. Since all reactions of 2 take place exclusively at C10, transannular H-bonding is concluded not to contribute significantly to the structure of 2. Diolepoxide reactions with both weak and strong nucleophiles and with DNA are discussed and the mechanisms interpreted in terms of molecular structure as determined by the theoretical calculations. 相似文献