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21.
试验在pH10.0~11.0条件下,用络天青S(CAS)和溴化十六烷基吡啶(CPB)、Tritonx—100与铍形成橙色四元络合物,其最大吸收波长为508nm,采用酒石酸、柠檬酸钠、EDTA、三乙醇胺等作为掩蔽剂,可消除多种共存离子的干扰直接测定多金属矿中微量氧化铍,本法灵敏度高(ε=3.75×104),稳定性及重现性较好,BeO含量在0~8μg/50ml符合比尔定律。 相似文献
22.
Abstract The present study shows that 20-hydroxyecdysone(20-OHE) participates in the humoral immune responses of Philosamia Cynthia ricini, either normal or debrained pupae, to the E. coli. The mode of action of 20—-OHE is multiple. It raises hemolymph protein content, makes antibacterial proteins be produced, increases lysozyme activity, and activates prophenoloxidase system. It is possible that several immune control systems are involved. 相似文献
23.
S. Aime Mauro Botta S. Geninatti Crich Giovanni B. Giovenzana Roberto Pagliarin Maurizio Piccinini Massimo Sisti Enzo Terreno 《Journal of biological inorganic chemistry》1997,2(4):470-479
A novel heptacoordinating ligand consisting of a thirteen-membered tetraazamacrocycle containing the pyridine ring and bearing
three methylenephosphonate groups (PCTP-[13]) has been synthesized. Its Gd(III) complex displays a remarkably high longitudinal
water proton relaxivity (7.7 mM–1 s–1 at 25 °C, 20 MHz and pH 7.5) which has been accounted for in terms of contributions arising from (1) one water molecule
bound to the metal ion, (2) hydrogen-bonded water molecules in the second coordination sphere, or (3) water molecules diffusing
near the paramagnetic chelate. Variable-temperature 17O-NMR transverse relaxation data indicate that the residence lifetime of the metal-bound water molecule is very short (8.0 ns
at 25 °C) with respect to the Gd(III) complexes currently considered as contrast agents for magnetic resonance imaging. Furthermore,
GdPCTP-[13] interacts with human serum albumin (HSA), likely through electrostatic forces. By comparing water proton relaxivity
data for the GdPCTP-[13]-HSA adduct, measured as a function of temperature and magnetic field strength, with those for the
analogous adduct with GdDOTP (a twelve-membered tetraaza macrocyclic tetramethylenephosphonate complex lacking a metal-bound
water molecule), it has been possible to propose a general picture accounting for the main determinants of the relaxation
enhancement observed when a paramagnetic Gd(III) complex is bound to HSA. Basically, the relaxation enhancement in these systems
arises from (1) water molecules in the hydration shell of the macromolecule and protein exchangeable protons which lie close
to the interaction site of the paramagnetic complex and (2) the metal bound water molecule(s). As far as the latter contribution
is concerned, the interaction with the protein causes an elongation of the residence lifetime of the metal-bound water molecule,
which limits, to some extent, the potential relaxivity enhancement expected upon the binding of the paramagnetic complex to
HSA.
Received: 27 January 1997 / Accepted: 12 May 1997 相似文献
24.
G Taudou G Mirambeau C Lavenot A der Garabedian J Vermeersch M Duguet 《FEBS letters》1984,176(2):431-435
Topoisomerase activities have been measured in nuclear extracts of concanavalin A-stimulated lymphocytes. In parallel with the wave of DNA synthesis, type II topoisomerase activity was considerably increased. After 72 h treatment, this activity was stimulated approx. 20-fold over the activity in untreated cells. In contrast, type I topoisomerase was poorly stimulated after 24 h treatment, and 4-5-fold after 72 h. These findings, together with our previous results on regenerating rat liver, suggest a major role of topoisomerase II in DNA replication. 相似文献
25.
Rafael Apitz-Castro Alicia De Murciano 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,544(3):529-539
32P phosphorylation of plasma membranes from human blood platelets, under conditions that closely resemble physiological ones (endogeneous phosphate donors and intact platelets in homologous plasma), result in the incorporation of the label mainly in a membrane glycoprotein of apparently high molecular weight (greater than 400 000). Dibutyryl cyclic AMP, an inhibitor of platelet aggregation, specifically increases the degree of phosphorylation of this glycoprotein. Moreover, it has been found that prostaglandin E1 one of the most potent inhibitors of platelet aggregation which also increases phosphorylation of the same glycoprotein, is significantly more effective than cyclic AMP.Cyclic GMP does not have any apparent effect on platelet aggregation. However, incubation of platelet-rich plasma with both cyclic GMP and cyclic AMP results in a partial recovery of the platelet responsiveness towards ADP-induced aggregation. Coincidently, the degree of phosphorylation of the high molecular weight glycoprotein under these conditions, although still higher than in controls (no nucleotides added), is significantly decreased as compared with cyclic AMP-treated cells. Furthermore, cyclic GMP inhibits the cyclic AMP-dependent protein kinase activity in isolated platelet plasma membranes.These results suggest a central role for this membrane phosphoglycoprotein in the triggering of platelet aggregation and, furthermore, suggest that modulation of its degree of phosphorylation may be exerted through some cyclic AMP/cyclic GMP relationship, which in the basal state might be critical for platelet responsiveness. 相似文献
26.
Treatment of Sendai virus with , followed by freezing and thawing resulted in a loss of hemolytic and cell fusion activities as well as infectivity without affecting hemagglutinating and neuraminidase activities. The anti-hemolytic activity of this compound was reversed by the addition of phosphatidyl choline to the virus samples. was successfully used for photoaffinity labeling of a specific virion site, and we confirmed the affected site of the glucoside to be the lipid components in the viral envelopes. 相似文献
27.
A new microsporidian species, Nosema pilicornis, which infects the purslane sawfly, Schizocerella pilicornis, is described. This microsporidium infects most body tissues of the host. N. pilicornis was compared to other microsporidian species infecting Hymenoptera and to a group of similar microsporidia infecting Lepidoptera. N. pilicornis could be distinguished from all other microsporidian species on the basis of host range and ultrastructural characteristics of the spore. Spores were oval, containing 11 to 12 polar filament coils, and the polar filament had an angle of tilt of about 80°. N. pilicornis infected lepidopteran larvae, but only when heavy spore dosages were fed to early larval instars. S. pilicornis is a good but sporadic biological control agent of common purslane, Portulaca oleracea, a pernicious weed of vegetable, ornamental, and orchard crops. N. pilicornis, which is transovarially transmitted and causes high mortality in infected larvae, affects the performance of S. pilicornis as a biological control agent. 相似文献
28.
The kinetics of the oxidation-reduction reactions of cytochrome c1 with ascorbate, ferricyanide, triphenanthrolinecobalt(III) and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) have been examined using the stopped-flow technique. The reduction of ferricytochrome c1 by ascorbic acid is investigated as a function of pH. It is shown that at neutral and alkaline pH the reduction of the protein is mainly performed by the doubly deprotonated form of ascorbate. From the ionic-strength-dependence studies of the reactions of cytochrome c1 with ascorbate, ferricyanide and triphenanthrolinecobalt(III), it is demonstrated that the reaction rate is governed by electrostatic interactions. The second-order rate constants for the reaction of cytochrome c1 with ascorbate, ferricyanide, TMPD and triphenanthrolinecobalt(III) are 1.4·104, 3.2·103, 3.8·104 and 1.3·108 M?1·s?1 (pH 7.0, I = 0, 10°C), respectively. Application of the Debye-Hückel theory to the the ionic-strength-dependence studies of these redox reactions of cytochrome c1 yielded for ferrocytochrome c1 and ferricytochrome c1 a net charge of ?5 and ?4, respectively. The latter value is close to that of ?3 for the oxidized enzyme, calculated from the amino acid sequence of the protein. This implies that not a local charge on the surface of the protein, but the overall net charge of cytochrome c1 governs the reaction rate with small redox molecules. 相似文献
29.
本文对光生物和光化学的定义,反应机制的类型和光敏化作用等做了阐述。下面例举几个光疗的成果 1.光疗牛皮癣 经常使用的8-甲氧基补骨脂素在UVA的照射下,从基态被激发到三重态。它主要和DNA中的胸腺嘧啶,其次和色氨酸进行光环合加成,形成交联,阻止DNA和RNA的合成,抑制具过度增生 2.血卟啉衍生物(HPD)治癌 HPD有定位于癌组织的能力和光动力作用,可推断病人体内癌部位。 讨论了HPD的光疗机制,和酞菁相比,有各自的优缺点。 3.竹红菌素 主要治疗妇女外阴白色病变和疤痕疙瘩,抑制癌细胞生长。 讨论了竹红菌甲素和乙素及它们的氧化物的结构和活性。 在大于510nm的光照射下,也可抑制癌细胞的生长。列举了竹红菌素的优缺点。 相似文献
30.
The antibacterial activities of isoflavonoid (kievitone and phaseollin), flavonoid (hydroxyflavans), furanoacetylenic (wyerone), and sesquiterpenoid (capsidiol and rishitin), phytoalexins against eight Gram-negative and six Gram-positive bacteria were examined using the paper-disc antibiotic assay method. With the exception of capsidiol, which was inactive at the highest concentration tested (200,μg/disc) all of the phytoalexins were selectively toxic towards Gram-positive species. Wyerone and kievitone were generally more toxic than other phytoalexins; rishitin was the least active inhibitor. 相似文献