Chemiluminescence assay for quinones based on generation of reactive oxygen species through the redox cycle of quinone

A sensitive and selective chemiluminescence assay for the determination of quinones was developed. The method was based on generation of reactive oxygen species through the redox reaction between quinone and dithiothreitol as reductant, and then the generated reactive oxygen was detected by luminol chemiluminescence. The chemiluminescence was intense, long-lived, and proportional to quinone concentration. It is concluded that superoxide anion was involved in the proposed chemiluminescence reaction because the chemiluminescence intensity was decreased only in the presence of superoxide dismutase. Among the tested quinones, the chemiluminescence was observed from 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 1,4-naphthoquinone, whereas it was not observed from 9,10-anthraquinone and 1,4-benzoquinone. The chemiluminescence property was greatly different according to the structure of quinones. The chemiluminescence was also observed for biologically important quinones such as ubiquinone. Therefore, a simple and rapid assay for ubiquinone in pharmaceutical preparation was developed based on the proposed chemiluminescence reaction. The detection limit (blank + 3SD) of ubiquinone was 0.05 μM (9 ng/assay) with an analysis time of 30 s per sample. The developed assay allowed the direct determination of ubiquinone in pharmaceutical preparation without any purification procedure. Figure Chemiluminescence generated through the redox cycle of quinone     

壁板颤振的分析模型、数值求解方法和研究进展

研究壁板颤振问题需要计及大挠度变形下结构的几何非线性效应,不仅涉及气动弹性稳定性,而且关心结构的非线性颤振响应.该文回顾了飞行器壁板颤振问题的国内外研究情况,评述了在壁板颤振研究中采用的分析模型、数值求解方法以及在理论分析和试验方面的研究成果,并提出了今后壁板颤振问题的4个研究方向.      

非等熵气体动力学方程组大初值问题的放缩框架

非等熵气体动力学系统Cauchy问题弱解全局存在性有两个公开问题:一个是包含真空的小初值问题,另一个是任意大初值问题.本文通过引入一个放缩框架证明了上述两个问题的等价性,即对于粘性消失解,其包含真空小初值问题的一致BV估计蕴含着任意大初值问题弱解的全局存在性.该放缩框架对大多数具有物理背景的双曲守恒律系统亦成立.     

Gypensapogenin H from hydrolyzate of total Gynostemma pentaphyllum saponins induces apoptosis in human breast carcinoma cells

Abstract

Gypensapogenin H (Gyp H) is a novel dammarane-type triterpene, isolated from hydrolyzate of total saponins from Gynostemma pentaphyllum. Our previous work demonstrated that Gyp H exhibited potent growth inhibitory effects on tumor cells. It significantly inhibited the growth of human breast cancer cells (MDA-MB-231), while having low toxicity to normal human breast epithelial cells, MCF-10a. Further mechanistic study demonstrated that Gyp H decreased survival, inhibited proliferation, migration, induced apoptosis and led to cell cycle arrest. For the MDA-MB-231 cell lines, Gyp H increased expression of P21, Bax and cytochrome c, induced PARP cleavage and activated caspases. Gyp H also reduced expression of CDK2/4, CyclinD1, E2F1 and Bcl2, which associated with the cell cycle arrest. Thus, our finding may be useful for understanding the mechanism of action of Gyp H on breast cancer cells and suggest that Gyp H would be a leading agent for the treatment of breast cancer.     

Geometric interpretation of Hamiltonian cycles problem via singularly perturbed Markov decision processes

We consider the Hamiltonian cycle problem (HCP) embedded in a singularly perturbed Markov decision process (MDP). More specifically, we consider the HCP as an optimization problem over the space of long-run state-action frequencies induced by the MDP's stationary policies. We also consider two quadratic functionals over the same space. We show that when the perturbation parameter, ? is sufficiently small the Hamiltonian cycles of the given directed graph are precisely the maximizers of one of these quadratic functionals over the frequency space intersected with an appropriate (single) contour of the second quadratic functional. In particular, all these maximizers have a known Euclidean distance of z _m (?) from the origin. Geometrically, this means that Hamiltonian cycles, if any, are the points in the frequency polytope where the circle of radius z _m (?) intersects a certain ellipsoid.     

Insights into the N-terminal Cu(II) and Cu(I) binding sites of the human copper transporter CTR1

Abstract

Copper transporter 1 (CTR1) is the main copper transporter in the eukaryotic system. CTR1 has several important roles: It binds Cu(II) ions that are present in the blood; it reduces those Cu(II) ions to Cu(I); and it subsequently transfers Cu(I) to the cytoplasmic domain, where the ion is delivered to various cellular pathways. Here, we seek to identify CTR1 binding sites for Cu(II) and Cu(I) and to shed light on the Cu(II)-to-Cu(I) reduction process. We focus on the first 14 amino acids of CTR1. This N-terminal segment is rich with histidine and methionine residues, which are known to bind Cu(II) and Cu(I), respectively; thus, this region has been suggested to have an important function in recruiting Cu(II) and reducing it to Cu(I). We utilize electron paramagnetic resonance (EPR) spectroscopy together with nuclear magnetic resonance (NMR) and UV-VIS spectroscopy and alanine substitution to reveal Cu(II) and Cu(I) binding sites in the focal 14-amino-acid segment. We show that H5 and H6 directly coordinate to Cu(II), whereas M7, M9, and M12 are involved in Cu(I) binding. This research is another step on the way to a complete understanding of the cellular copper regulation mechanism in humans.