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91.
Bai R Nguyen TL Burnett JC Atasoylu O Munro MH Pettit GR Smith AB Gussio R Hamel E 《Journal of chemical information and modeling》2011,51(6):1393-1404
Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds. 相似文献
92.
Ernest Nieznaj 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2011,62(2):223-231
In this paper, we investigate the trajectory of the passive tracer model governed by the ordinary differential equation $$ \frac{{\rm d} {\bf x} (t)}{{\rm d}t} = {\bf F} ({\bf x}(t)), \quad {\bf x}(0)= {\bf x}_{0}, $$ where F(x) is a zero mean, homogeneous, isotropic Poisson shot noise random field. We prove the superdiffusive character of the trajectories under certain conditions on the energy spectrum of the velocity field. 相似文献
93.
Alves L Ballesteros B Boronat M Cabrero-Antonino JR Concepción P Corma A Correa-Duarte MA Mendoza E 《Journal of the American Chemical Society》2011,133(26):10251-10261
Small gold nanoclusters in a very narrow size distribution (1.1 ± 0.5 nm) have been stabilized onto multiwalled carbon nanotubes (MWCNT). Theoretical studies supported by XPS and (16)O(2)/(18)O(2) isotopic exchange experiments have shown that, on small gold nanoparticles (0.9-1.5 nm), dissociation of molecular O(2) and formation of a surface oxide-like layer is energetically favorable and occurs at room temperature, while O(2) recombination and desorption involves a larger activation barrier. CO titration experiments and theoretical studies demonstrate that the reactivity of the oxidized particles toward CO does not only depend on particle size but also on oxygen coverage. The oxidation-reduction process described is reversible, and the oxidized nanoparticles are active in the epoxidation of styrene with air. 相似文献
94.
95.
Miroslav Stredanský Lubomir Kremnický Ernest Sturdik Anna Fecková 《Applied biochemistry and biotechnology》1993,38(3):269-276
Production of α-amylase withB. subtilis CCM 2722 in an aqueous two-phase polyethylene glycol/dextran system integrated with product purification by affinity chromatography on crosslinked starch during cultivation was studied. The medium was drawn from the bioreactor to the external settler during fermentation. After phase separation in the settler the dextran-rich bottom phase with cells was returned to the bioreactor. The PEG-rich top phase was pumped to the column with crosslinked starch and returned to the bioreactor after α-amylase adsorption. The same volumetric productivities, 0.53 U/mL/h, were reached in both batch and described process, but total productivity of the latter method was much higher owing to shortening upstream and downstream processing time. The enzyme of 98% homogenity in 95% yield was obtained after its elution from the column. 相似文献
96.
97.
Shin Y Fournier JH Brückner A Madiraju C Balachandran R Raccor BS Edler MC Hamel E Sikorski RP Vogt A Day BW Curran DP 《Tetrahedron》2007,63(35):8537-8562
Total syntheses of (−)-dictyostatin, 6,16-bis-epi-dictyostatin, 6,14,19-tris-epi-dictyostatin, and a number of other isomers and analogs are reported. Three main fragments—top, middle, and bottom—were first assembled and then joined by olefination or anionic addition reactions. After appending the two dienes at either end of the molecule, macrolactonization and deprotection completed the syntheses. The work proves both the relative and absolute configurations of (−)-dictyostatin. The compounds were evaluated by cell-based measurements of increased microtubule mass and antiproliferative activity, and in vitro tubulin polymerization assays as well as competitive assays with paclitaxel for its binding site on microtubules. These assays showed dictyostatin to be the most potent of the agents and further showed that the structural alterations caused from 20- to >1000-fold decreases in activity. 相似文献
98.
The problem of identification in fuzzy systems described by the use of fuzzy equation is considered. The identification method and its performance index is also presented. The formal procedure of the identification algorithm is illustrated by means of a numerical example. The possibility of using the proposed algorithm for the solution of a control problem is given as well. 相似文献
99.
100.
The overall photobromination reactions have been studied using a competitive technique. Relative Arrhenius parameters were obtained for the rate-determining step These were placed on an absolute basis using previous-absolute values of A and E for RFI=CF3I. The activation energies were used to calculate bond dissociation energies D(R? I) with the following results:
RF? | E16 | D(RF?I)(kcal/mole) |
---|---|---|
CF3I a a E16 from [1] | 10.8 | 52.6 |
C2F5I | 8.8 | 50.6 |
n-C3F7I | 7.4 | 49.2 |
i-C3F7I | 7.5 | 49.2 |
n-C4F9I | 6.7 | 48.4 |
- a E16 from [1]