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991.
QM/MM modeling of the hydroxylation of the androstenedione substrate catalyzed by cytochrome P450 aromatase (CYP19A1) 下载免费PDF全文
Ignacio Viciano Raquel Castillo Sergio Martí 《Journal of computational chemistry》2015,36(23):1736-1747
CYP19A1 aromatase is a member of the Cytochrome P450 family of hemeproteins, and is the enzyme responsible for the final step of the androgens conversion into the corresponding estrogens, via a three‐step oxidative process. For this reason, the inhibition of this enzyme plays an important role in the treatment of hormone‐dependent breast cancer. The first catalytic subcycle, corresponding to the hydroxilation of androstenedione, has been proposed to occur through a first hydrogen abstraction and a subsequent oxygen rebound step. In present work, we have studied the mechanism of the first catalytic subcycle by means of hybrid quantum mechanics/molecular mechanics methods. The inclusion of the protein flexibility has been achieved by means of Free Energy Perturbation techniques, giving rise to a free energy of activation for the hydrogen abstraction step of 13.5 kcal/mol. The subsequent oxygen rebound step, characterized by a small free energy barrier (1.5 kcal/mol), leads to the hydroxylated products through a highly exergonic reaction. In addition, an analysis of the primary deuterium kinetic isotopic effects, calculated for the hydrogen abstraction step, reveals values (~10) overpassing the semiclassical limit for the C? H, indicating the presence of a substantial tunnel effect. Finally, a decomposition analysis of the interaction energy for the substrate and cofactor in the active site is also discussed. According to our results, the role of the enzymatic environment consists of a transition state stabilization by means of dispersive and polarization effects. © 2015 Wiley Periodicals, Inc. 相似文献
992.
Yuelong Ma 《Tetrahedron letters》2009,50(30):4343-4345
A concise synthesis of indolic enamides coscinamide A, coscinamide B, and the brominated tryptamine derivative igzamide is described. Both E- and Z-isomers of these natural compounds were obtained during the thermally assisted dehydration reaction and were tested for antitumor activity. Coscinamide B was found to possess antitumor activity against DU145 with an IC50 of 7.6 μg/mL. 相似文献
993.
Chunmei Zhang Zhijia Liu Yongming Li Qi Li Chaojun Song Zhuwei Xu Yun Zhang Yusi Zhang Ying Ma Yuanjie Sun Lihua Chen Liang Fang Angang Yang Kun Yang Boquan Jin 《Analytica chimica acta》2013
In this study, detection of staphylococcal enterotoxin A (SEA) in multi-matrices using a highly sensitive and specific microplate chemiluminescence enzyme immunoassay (CLEIA) has been established. A pair of monoclonal antibodies (mAbs) was selected from 37 anti-SEA mAbs by pairwise analysis, and the experimental conditions of the CLEIA were optimized. This CLEIA exhibited high performance with a wide dynamic range from 6.4 pg mL−1 to 1600 pg mL−1, and the measured low limit of detection (LOD) was 3.2 pg mL−1. No cross-reactivity was observed when this method was applied to test SEB, SEC1, and SED. It has also been successfully applied for analyzing SEA in a variety of environmental, biological, and clinical matrices, such as sewage, tap water, river water, roast beef, peanut butter, cured ham, 10% nonfat dry milk, milk, orange juice, human urine, and serum. Thus, the highly sensitive and SEA-specific CLEIA should make it attractive for quantifying SEA in public health and diagnosis in near future. 相似文献
994.
Determination of bisphenol A based on chemiluminescence from gold(III)-peroxymonocarbonate 总被引:1,自引:0,他引:1
Peroxymonocarbonate (HCO4−) was produced by the online reaction of bicarbonate with hydrogen peroxide. A strong chemiluminescence (CL) was observed when HCO4− reacted with AuCl4− without any special CL reagent. When bisphenol A (BPA) was added to AuCl4−-HCO4− CL system, the CL emission was inhibited significantly. This new CL system was developed as a flow-injection method for the determination of BPA. Under the optimum experimental conditions, the inhibited CL intensity was linearly related to the concentration of BPA from 0.3 to 80 μM (R = 0.9958). The detection limit of BPA was 0.08 μM. The relative standard deviation for 12 repeated measurements of 1.0 μM BPA was 2.9%. The interferences of some cationic ions can be removed by an online cation-exchange column. The applicability of the present CL system was demonstrated for the sensitive and selective determination of BPA in real samples (mineral water bottle, baby bottle, beverage bottle and polycarbonate container). Based on the CL spectrum, UV-visible adsorption spectra, and the quenching effect of reactive oxygen species scavengers, a possible CL mechanism was proposed. 相似文献
995.
A method for determination of intracellular acyl‐coenzyme A esters in Clostridium acetobutylicum (CA) by high performance liquid chromatography (HPLC) was developed and validated. In our experiment, two important intermediates acyl‐coenzyme A esters including acetyl‐CoA, butyryl‐CoA could be baseline separated on a Zobax‐C18 column with mobile phase composed of the acetonitrile and phosphate buffer (pH 5.0). Samples treated with freeze‐thaw and protein precipitated by addition of trichloroacetic acid could be directly injected for determination of acetyl‐CoA, butyryl‐CoA with a recovery higher than 73%. With this method, the metabolite profiling of the acyl‐coenzyme A esters of CA was obtained. The comparison of the metabolite profiling between the model strain ATCC 824 and a mutant strain EA 2018, which produces higher butanol than the former was performed. Some useful information was concluded for understanding the mechanism of CA for selectively producing the solvent. 相似文献
996.
Jian Xiao Li-Bin Lin Jia-Yao Hu Dong-Zhu Duan Wei Shi Qiang Zhang Wen-Bo Han Le Wang Xiao-Ling Wang 《Tetrahedron letters》2018,59(18):1772-1775
Pestalustaines A (1) and B (2), one unique sesquiterpene possessing an unusual 5/6/7-fused tricyclic ring system and one unprecedented coumarin derivative bearing 6/6/5/5-fused tetracyclic ring system, were isolated from the plant-derived Pestalotiopsis adusta. Their structures with absolute configurations were established by extensive NMR analysis, X-ray crystallography, and CD spectra associated with TD-DFT calculation. Hypothetical biosynthetic pathways for compounds 1 and 2 are proposed. Compounds 1 and 2 showed weak to moderate cytotoxic activities against three human tumor cell lines HeLa, HCT116, and A549, whose IC50 values were ranged from 21.01 to 55.43?μM. 相似文献
997.
In order to further study on minor diterpenoid constituents of lsodon rubescens, wereinvestigated this species, which was collected in Taibai mountain, Shaanxi Province.TWo new diterpenoids, taibairubescensins A (l) and B (2), were isolated. In this paper,we present the structure elucidation of these two new diterpenoids.Taibairubescensin A (l ), C,.H,#O, (FABMS m/z 435[M 11 ), an amorphous powder,showed UV and iR absorption bands for the existence of hydroxyl, acetoxyl and a fivemembe… 相似文献
998.
999.
James Kao 《Journal of Molecular Structure》1980,63(2):293-300
The structures of S42+ and S42? have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S42? was also investigated. The anti chain form of S42+ was found to be 78.3 kJ mol? more stable than the square form, in contrast to previous experimental data. S42?is predicted to adopt the chain structure with the anti conformation. 相似文献
1000.
The mechanism and stereochemistry of δ-C atom functionalisation in the reactions of secondary straight-chain aliphatic alcohols with lead tetraacetate, ceric ammonium nitrate, and heavy metal (Pb4+, Hg2+, Ag+) salts (AcO)?1, O2?, CO32?-halogen (I2, Br2, Cl2) combinations are discussed. By demonstrating the intermediacy of 5-bromo-2-hexanol, it was confirmed that the dark silver oxidebromine induced cyclisation of 2-hexanol (and alcohols in general) involves (as the other hypohalite reactions) intramolecular 1,5-hydrogen abstraction by alkoxy radicals and formation of δ-bromohydrins. A novel and simple procedure for obtaining tetrahydrofurans from alcohols by way of the hypochlorite reaction, using silver or mercuric salts and chlorine, is described. 相似文献