Comparative study of the efficacies of nine assay methods for the dextransucrase synthesis of dextran

A comparative study of nine assay methods for dextransucrase and related enzymes has been made. A relatively widespread method for the reaction of dextransucrase with sucrose is the measurement of the reducing value of d-fructose by alkaline 3,5-dinitrosalicylate (DNS) and thereby the amount of d-glucose incorporated into dextran. Another method is the reaction with ¹⁴C-sucrose with the addition of an aliquot to Whatman 3MM paper squares that are washed three times with methanol to remove ¹⁴C-d-fructose and unreacted ¹⁴C-sucrose, followed by counting of ¹⁴C-dextran on the paper by liquid scintillation counting (LSC). It is shown that both methods give erroneous results. The DNS reducing value method gives extremely high values due to over-oxidation of both d-fructose and dextran, and the ¹⁴C-paper square method gives significantly low values due to the removal of some of the ¹⁴C-dextran from the paper by methanol washes. In the present study, we have examined nine methods and find two that give values that are identical and are an accurate measurement of the dextransucrase reaction. They are (1) a ¹⁴C-sucrose/dextransucrase digest in which dextran is precipitated three times with three volumes of ethanol, dissolved in water, and added to paper and counted in a toluene cocktail by LSC; and (2) precipitation of dextran three times with three volumes of ethanol from a sucrose/dextransucrase digest, dried, and weighed. Four reducing value methods were examined to measure the amount of d-fructose. Three of the four (two DNS methods, one with both dextran and d-fructose and the other with only d-fructose, and the ferricyanide/arsenomolybdate method with d-fructose) gave extremely high values due to over-oxidation of d-fructose, d-glucose, leucrose, and dextran.     

Disparate degrees of hypervariable loop flexibility control T-cell receptor cross-reactivity, specificity, and binding mechanism

αβ T-cell receptors (TCRs) recognize multiple antigenic peptides bound and presented by major histocompatibility complex molecules. TCR cross-reactivity has been attributed in part to the flexibility of TCR complementarity-determining region (CDR) loops, yet there have been limited direct studies of loop dynamics to determine the extent of its role. Here we studied the flexibility of the binding loops of the αβ TCR A6 using crystallographic, spectroscopic, and computational methods. A significant role for flexibility in binding and cross-reactivity was indicated only for the CDR3α and CDR3β hypervariable loops. Examination of the energy landscapes of these two loops indicated that CDR3β possesses a broad, smooth energy landscape, leading to rapid sampling in the free TCR of a range of conformations compatible with different ligands. The landscape for CDR3α is more rugged, resulting in more limited conformational sampling that leads to specificity for a reduced set of peptides as well as the major histocompatibility complex protein. In addition to informing on the mechanisms of cross-reactivity and specificity, the energy landscapes of the two loops indicate a complex mechanism for TCR binding, incorporating elements of both conformational selection and induced fit in a manner that blends features of popular models for TCR recognition.     

The double-length tyrosyl-tRNA synthetase from the eukaryote Leishmania major forms an intrinsically asymmetric pseudo-dimer

The single tyrosyl-tRNA synthetase (TyrRS) gene in trypanosomatid genomes codes for a protein that is twice the length of TyrRS from virtually all other organisms. Each half of the double-length TyrRS contains a catalytic domain and an anticodon-binding domain; however, the two halves retain only 17% sequence identity to each other. The structural and functional consequences of this duplication and divergence are unclear. TyrRS normally forms a homodimer in which the active site of one monomer pairs with the anticodon-binding domain from the other. However, crystal structures of Leishmania major TyrRS show that, instead, the two halves of a single molecule form a pseudo-dimer resembling the canonical TyrRS dimer. Curiously, the C-terminal copy of the catalytic domain has lost the catalytically important HIGH and KMSKS motifs characteristic of class I aminoacyl-tRNA synthetases. Thus, the pseudo-dimer contains only one functional active site (contributed by the N-terminal half) and only one functional anticodon recognition site (contributed by the C-terminal half). Despite biochemical evidence for negative cooperativity between the two active sites of the usual TyrRS homodimer, previous structures have captured a crystallographically-imposed symmetric state. As the L. major TyrRS pseudo-dimer is inherently asymmetric, conformational variations observed near the active site may be relevant to understanding how the state of a single active site is communicated across the dimer interface. Furthermore, substantial differences between trypanosomal TyrRS and human homologs are promising for the design of inhibitors that selectively target the parasite enzyme.     

喀斯特石漠化区不同小生境常见灌木种叶片δ13C值特征

测定了喀斯特石漠化区不同小生境内5种常见灌木（鼠李、火棘、粉枝莓、竹叶椒和烟管荚蒾）的叶片δ¹³C值,探讨喀斯特石漠化对植物水分利用空间异质性的影响.结果表明： 不同小生境植物的δ¹³C均值大小顺序为：石面>石沟>石缝>土面.土面生境中多数灌木种植株叶片δ¹³C值较其他生境偏轻;灌木叶片δ¹³C值大小顺序为：烟管荚蒾＞粉枝莓＞竹叶椒＞火棘＞鼠李.各小生境内灌木叶片δ¹³C均值和主要灌木种叶片δ¹³C值均随着石漠化加深而增大,且不同小生境间差异显著.随着石漠化的加剧,喀斯特生境结构和功能受损,小生境逐渐分异,环境逐渐向着干旱化发展.     

Effects of biodrying process on municipal solid waste properties

In this paper, the effect of biodrying process on municipal solid waste (MSW) properties was studied. The results obtained indicated that after 14 d, biodrying reduced the water content of waste, allowing the production of biodried waste with a net heating value (NHV) of 16,779 ± 2,074 kJ kg⁻¹ wet weight, i.e. 41% higher than that of untreated waste. The low moisture content of the biodried material reduced, also, the potential impacts of the waste, i.e. potential self-ignition and potential odors production. Low waste impacts suggest to landfill the biodried material obtaining energy via biogas production by waste re-moistening, i.e. bioreactor. Nevertheless, results of this work indicate that biodrying process because of the partial degradation of the organic fraction contained in the waste (losses of 290 g kg⁻¹ VS), reduced of about 28% the total producible biogas.     

人类疾病动物模型是医药创新研究的前沿

人类疾病动物模型对医药研究起着支撑作用,是进行医药研究的必备工具之一.本文阐述了人类疾病动物模型在医药研究中所能发挥的作用,以及在医药研究的历史中所做出的贡献.最后,对疾病动物模型在医药创新研究中应用的前沿进行了展望.     

Brain and systemic glucose metabolism in the healthy elderly following fish oil supplementation

Cerebral metabolic rate of glucose (CMRg) is lower in individuals affected by cognitive decline and dementia, especially in Alzheimer's disease. However, as yet there is no consensus as to whether CMRg decreases during healthy aging. Epidemiological studies show that weekly consumption of fish abundant in ω3 fatty acids has a protective effect on cognition during aging. Thus, the primary objective of this human study was to use positron emission tomography analysis with (18)F-fluorodeoxyglucose to evaluate whether supplementation with a fish oil rich in ω3 fatty acids increases cerebral glucose metabolism in young or elderly adults. Healthy young (23±5y old; n=5) and elderly (76±3y old; n=6) women and men were included in the study. Semi-quantitative expression of the data as 'standardized uptake values' showed that elderly participants had significantly lower cerebral glucose metabolism compared with the young group. However, when expressed quantitatively a CMRg, there was no effect of age or ω3 supplementation on glucose metabolism in any of the brains regions studied. Higher plasma triglyceride levels and higher plasma insulin levels were associated with lower CMRg in several regions, suggesting that a trend towards the metabolic syndrome may be associated with cerebral hypometabolism. We conclude that under these experimental conditions, ω3 supplementation did not affect brain glucose metabolism in the healthy elderly. Future studies in this area should address whether glucose intolerance or other conditions linked to the metabolic syndrome impact negatively on brain glucose metabolism and cognition.     

Secure Similar Image Search and Copyright Protection over Encrypted Medical Image Databases

The recent advances in digital medical imaging and storage in cloud are bringing about more demands for efficient and secure image retrieval and management. Typically, medical images are very sensitive to changes where any modifications in its content may bring about an erroneous medical diagnosis. Therefore, securing medical images is a very essential process and the major task is, the medical image must maintain their sensitive contents at the time of reconstruction. The proposed methodology executes a secure image encryption and search of medical images proficiently over encrypted image database without leaking any sensitive data. It also ensures medical data integrity by introducing an efficient recovery mechanism on ROI of the image. The proposed scheme obtains recovery information about the image from the ROI of the medical data and embeds it in the RONI region using IWT transform which act as a reversible watermarking. If any alterations or tampers are caused to ROI at the third-party end, then it can be identified and recovered from the obtained recovery data. Besides, the model also executes a Copyright protection scheme to locate the authorized users, who illegally duplicate and distribute the retrieved image to unauthorized entities.     

Anatomy dissections and student experience at Irish universities, c.1900s-1960s

Utilising the unique source of articles, poems, stories and cartoons from student magazines from all of the Irish universities, in addition to the memoirs of Irish doctors, and the accounts of correspondents, this paper will discuss the Irish student’s experience of anatomy in the early twentieth century. For many medical students, anatomy dissections were seen as a rite of passage, while one student at Queen’s College Belfast claimed that ‘the dissecting-room is to the student a club, a smoke room, common room research room—one in all.’ However, the dissecting rooms of Irish medical schools were often rife with bawdy conversation, sexual undertones and black humour. Recognising this, following the admission of women to Irish medical schools from the 1880s, university authorities constructed separate dissecting rooms for the women students, and part of this paper will investigate why this separation occurred.I will examine the Irish dissecting room as a centre of learning and integral part of student experience in the period. The paper will suggest that the black humour and pranks that were commonplace within the context of the dissecting room acted as a means for students to reconcile their fears and anxiety about dissecting.     

Dr. Auzoux's botanical teaching models and medical education at the universities of Glasgow and Aberdeen

In the 1860s, Dr. Louis Thomas Jérôme Auzoux introduced a set of papier-mâché teaching models intended for use in the botanical classroom. These botanical models quickly made their way into the educational curricula of institutions around the world. Within these institutions, Auzoux’s models were principally used to fulfil educational goals, but their incorporation into diverse curricula also suggests they were used to implement agendas beyond botanical instruction. This essay examines the various uses and meanings of Dr. Auzoux’s botanical teaching models at the universities of Glasgow and Aberdeen in the nineteenth century. The two main conclusions of this analysis are: (1) investing in prestigious scientific collections was a way for these universities to attract fee-paying students so that better medical accommodation could be provided and (2) models were used to transmit different kinds of botanical knowledge at both universities. The style of botany at the University of Glasgow was offensive and the department there actively embraced and incorporated ideas of the emerging new botany. At Aberdeen, the style of botany was defensive and there was some hesitancy when confronting new botanical ideas.