Spectrophotometric determination of peptide transport with chromogenic peptide mimetics

A spectrophotometric assay to determine peptide transport has been developed. Using two chromogenic peptide mimetics, L-phenylalanyl-L-2-sulfanilylglycine (PSG) and L-phenylalanyl-L-3-thiaphenylalanine (PSP), the peptide transport patterns in individual cell species can be evaluated effectively. After the addition of PSG to a HeLa cell suspension, sulfanilic acid accumulated progressively inside, but not outside, the cells, demonstrating that PSG was transported wholly intact. The addition of PSP to the same cell suspension was followed immediately by extracellular thiophenol production. Measurement of the rate of thiophenol release thereby provided direct determination of PSP transport. The thiophenol release was consistent with Michaelis-Menten kinetics, with a K(m) of 0.016 mM and a V(max) of 5.07 nmol/min (1 x 10(6) cells/ml, pH 7.4, 37 degrees C). The resulting kinetic constants estimated were in agreement with values determined by single-substrate enzyme kinetics. Using PSP, transport kinetics of various dipeptides was examined by competitive spectrophotometry. As a result, dipeptides tested could be ranked in order of kinetic power for their transport.     

Challenges in calculation of the gamma index in radiotherapy – Towards good practice

The gamma index (γ) is one of the most commonly used metrics for the verification of complex modulated radiotherapy. The mathematical definition of the γ is computationally expensive and various techniques have been reported to speed up the calculation either by mathematically refining the γ or employing various computational techniques. These techniques can cause variation in output with different software implementations. The γ has traditionally been used to compare a 2D measured plane against a 2D or 3D dose distribution. Recently, software algorithm and hardware improvements have led to the possibility of using measured 2D data from commercial detector arrays to reconstruct a 3D-dose distribution and perform a volumetric comparison against the treatment planning system (TPS). A limitation in this approach is that commercial detector arrays have so far been limited by their spatial resolution which may affect the accuracy of the reconstructed 3D volume and subsequently the γ calculation. Additionally, 3D versus 3D γ comparison adds a layer of complication in the calculation of the γ given the increase in the number of calculation points and the result cannot be as easily interpreted in the same way as 2D comparison. This review summarises and highlights the computational challenges of the γ calculation and sheds light on some of these issues by means of a bespoke MATLAB software to demonstrate the impact of interpolation, γ search distance, resolution and 2D and 3D calculations. Finally, a recommendation is made on the minimum information that should be reported when publishing γ results.     

Microcystins: Synthesis and structure–activity relationship studies toward PP1 and PP2A

Microcystins are highly toxic cyanotoxins responsible for plant, animal and human poisoning. Exposure to microcystins, mainly through drinkable water and contaminated food, is a current world health concern. Although it is quite challenging, the synthesis of these potent cyanotoxins, analogs and derivatives helps to evaluate their toxicological properties and to elucidate their binding mechanisms to their main targets Protein Phosphatase-1 (PP1) and -2A (PP2A). This review focuses on synthetic approaches to prepare microcystins and analogs and compiles structure–activity relationship (SAR) studies that describe the unique features of microcystins that make them so potent.     

Virus-induced gene silencing in detached tomatoes and biochemical effects of phytoene desaturase gene silencing

Virus-induced gene silencing (VIGS) is a technology that has rapidly emerged for gene function studies in plants. Many advances have been made in applying this technique in an increasing number of crops. Recently, VIGS has been successfully used to silence genes in tomato fruit through agroinfiltration of fruit attached to the plant. The phytoene desaturase (Pds) gene has been widely used as a reporter gene in VIGS experiments, although little is known about the changes that occur due to its silencing in plants. In this paper, we describe the efficient silencing of the Pds gene through the VIGS approach in detached tomato fruits, which makes the VIGS procedure even more versatile and applicable. After 16 days of agroinfiltration, approximately 75% of the tomatoes showed Pds silencing symptoms, although the distribution of silenced areas was variable among fruits. To study the potential effects caused by Pds silencing in detached tomatoes, carotenoids and other semi-polar secondary metabolites were analyzed using Liquid Chromatography-Mass Spectrometry. In addition, potential differences in primary metabolites were analyzed using Gas Chromatography-Mass Spectrometry. The results indicated that the yellow phenotype observed in Pds-silenced fruit was mainly due to the lack of the red-colored lycopene and therefore to a more pronounced contribution of the yellow-orange carotenoids (lutein, violaxanthin, and zeaxanthin) to the final color of the fruits. Furthermore, the biochemical changes observed in Pds-silenced detached tomatoes suggested that carotenoid and other pathways, e.g. leading to alkaloids and flavonoids, might be affected by the silencing of this reporter gene, and this should be taken into consideration for future experimental designs.     

丝绸之路经济带核心区新疆城镇建设用地扩展的时空演变特征及影响机理

将丝绸之路经济带核心区新疆城镇建设用地扩展作为一个时空变化系统进行分析,提取1980—2015年7个年份用地演变信息,结合10 km×10 km方格网构建,从总量趋势、分地州市级区域、分用地类型及特殊性全面认知扩展的时空演变特征,采用地理探测器模型,在县域尺度定量诊断城镇建设用地扩展的人文要素和自然要素的影响程度及各要素间的交互影响作用,进而识别其主控要素并探讨其作用机理,对比分析天山北坡城市群和喀什都市圈两个重点发展区域的分异性。研究结果表明:近35年以来,丝绸之路经济带核心区新疆城镇建设用地扩展约2.9倍,扩展强度波动增长且以分散小斑块为主,各地州市扩展规模和强度的时空差异性显著,次一级城镇建设用地类型扩展呈现动态变化特征,用地扩展受自然本底胁迫条件和经济社会发展过程多重影响有其特殊性;全域城镇建设用地在县域尺度以低水平扩展与各级人文要素和自然要素水平的耦合匹配关系为主;综合地理探测器因子分析模块和交互作用模块的探测结果,判定地形位指数、城镇化率、地形起伏度、二三产业比重为影响丝绸之路经济带核心区新疆县域城镇建设用地扩展的主控要素,并探寻各主控要素的作用机理;在重点发展区域天山北坡城市群和喀什都市圈的驱动要素有共性也有明显分异性。该研究为丝绸之路经济带核心区新疆城镇建设用地因地因城因类的差别化调控及区域可持续发展提供科学支撑和决策依据。     

Detector location selection based on VIP analysis in near-infrared detection of dural hematoma

Detection of dural hematoma based on multi-channel near-infrared differential absorbance has the advantages of rapid and non-invasive detection. The location and number of detectors around the light source are critical for reducing the pathological characteristics of the prediction model on dural hematoma degree. Therefore, rational selection of detector numbers and their distances from the light source is very important. In this paper, a detector position screening method based on Variable Importance in the Projection (VIP) analysis is proposed. A preliminary modeling based on Partial Least Squares method (PLS) for the prediction of dural position μ_a was established using light absorbance information from 30 detectors located 2.0–5.0?cm from the light source with a 0.1?cm interval. The mean relative error (MRE) of the dural position μ_a prediction model was 4.08%. After VIP analysis, the number of detectors was reduced from 30 to 4 and the MRE of the dural position μ_a prediction was reduced from 4.08% to 2.06% after the reduction in detector numbers. The prediction model after VIP detector screening still showed good prediction of the epidural position μ_a. This study provided a new approach and important reference on the selection of detector location in near-infrared dural hematoma detection.     

氨基酸的毛细管电泳检测研究新进展

氨基酸是生命有机体的重要组成部分,参与人体各项生理活动和新陈代谢,在人体中发挥着特殊的作用,是人体必不可少的营养成分之一。近年来,生命科学的研究与食品、药品和保健品的开发,以及麻醉药品、精神药品对兴奋性神经递质的影响的研究,促进了对存在于各种检验材料中的氨基酸的分析方法的研究,探索高灵敏度和高选择性的氨基酸分析检测方法引起了人们极大的兴趣,所以建立快速、准确的氨基酸的检测方法越来越重要。毛细管电泳(capillary electrophoresis,CE)是继高效液相色谱之后发展起来的一种新的分离和分析方法,具有分离效率高、分析速度快、样品及试剂用量少等特点,本文参考近几年的相关文献,对氨基酸进行毛细管电泳检测使用紫外检测器、荧光检测器、电化学检测器和质谱检测器的方法作一综述。