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31.
32.
Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers 总被引:4,自引:0,他引:4
Controlled chemical modification of enzymes, targeting groups not involved
in the active site, can lead to modified catalysts that are intrinsically
more efficient and resistant to heat and denaturing agents. Bovine
pancreatic trypsin was covalently modified up to 75-85% with monomeric
glutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose and
oxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss in
activity occurred upon modification. Temperature optima of trypsin shifts
from 45-76 degrees C and T50 from 54-76 degrees C for the best modified
sample made with OSP. The efficiency of the modifiers in stabilization was
ranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T >
Sucrose-T. Half-life of modified enzymes also followed the same trend. Both
stabilization factor and t1/2 decreased with increasing temperatures. The
free energy of activation for inactivation delta(deltaG*) varies from 12-20
kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsin
by 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsin
by urea is less noticeable. The character of the two-step inactivation
process of trypsin changes with the degree of stabilization in that the
duration of phase I one increased noticeably as stabilization increases.
Native trypsin fluoresces less intensely showing a red shift under the
influence of denaturation. Such a fluorescence change is not so obvious for
the modified enzymes indicating conformational stability acquired by
modification.
相似文献
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35.
Suddhasattwa Ghosh S. Vandarkuzhali Nibedita Gogoi P. Venkatesh G. Seenivasan B. Prabhakara Reddy K. Nagarajan 《Electrochimica acta》2011,(24):8204
The anodic dissolution of U and Zr metal was studied in LiCl–KCl–UCl3 and LiCl–KCl–ZrCl4, respectively, at 773 K by cyclic voltammetry and compared with their respective dissolution behaviour in blank LiCl–KCl eutectic. The anodic dissolution of U–Zr alloy in LiCl–KCl–UCl3 was also studied at 773 K to compare with the dissolution of U and Zr. The transfer coefficients evaluated by Tafel analysis and the method of Allen–Hickling for U and Zr dissolution were found to be in fair agreement with each other. U dissolution in LiCl–KCl–UCl3 and Zr dissolution LiCl–KCl–ZrCl4 were also studied by chronoamperometry and the diffusion coefficient value of U3+ was calculated to be in the range of 2.9 × 10−5 to 3.3 × 10−5 cm2 s−1 which is in agreement with those reported in literature. Convolution voltammetric analysis of Zr4+/Zr2+ redox couple in LiCl–KCl–ZrCl4 was carried out for the first time to have a comprehensive understanding of the electrode kinetics. 相似文献
36.
Shahram Emami Venkatesh Meda Robert T. Tyler 《International Journal of Food Science & Technology》2011,46(2):421-428
The effect of micronisation (high‐intensity infrared heating) and microwave radiation of normal barley (NB), high‐amylose barley (HAB) and waxy barley (WB) on the physical and mechanical properties was studied. Samples were tempered to 42–45% moisture content and then subjected to infrared or microwave radiation to reduce the moisture content to approximately 10%. The grain surface temperature during radiation was maintained at 100 °C. The changes in physical and mechanical properties were compared with unprocessed samples. Thermal radiation increased slightly the volume of the kernels because of the diffusion of water vapour from inside to the outer surface. These changes resulted in a decrease in particle and bulk densities. Thermal radiation affected the Hunter colour values, as well. The mechanical properties including bio‐yield point, modulus of elasticity and breakage susceptibility were affected by micronisation and microwave heating. 相似文献
37.
Thin Nguyen Dinh Phung Brett Adams Svetha Venkatesh 《Knowledge and Information Systems》2014,39(3):667-702
We present a large-scale mood analysis in social media texts. We organise the paper in three parts: (1) addressing the problem of feature selection and classification of mood in blogosphere, (2) we extract global mood patterns at different level of aggregation from a large-scale data set of approximately 18 millions documents (3) and finally, we extract mood trajectory for an egocentric user and study how it can be used to detect subtle emotion signals in a user-centric manner, supporting discovery of hyper-groups of communities based on sentiment information. For mood classification, two feature sets proposed in psychology are used, showing that these features are efficient, do not require a training phase and yield classification results comparable to state of the art, supervised feature selection schemes; on mood patterns, empirical results for mood organisation in the blogosphere are provided, analogous to the structure of human emotion proposed independently in the psychology literature; and on community structure discovery, sentiment-based approach can yield useful insights into community formation. 相似文献
38.
In the processing of multilayer ceramic multichip modules (MCM's), a ceramic substrate, such as alumina, along with a polymer, such as poly(methyl methacrylate) (PMMA), solvents, plasticizers, flocculants, is thermally degraded before sintering. The thermal degradation of PMMA from the green body of oxide ceramics leaves behind some amount of residual carbon in the ceramic. Carbon concentration above 100 ppm has a deleterious effect on the physical properties such as fkxural strength, density, breakdown voltage and dcnsification behavior of the ceramic. This paper discusses the kinetics of oxidation of carbon formed by the thermal degradation of poly(methyt methacrylate) in alumina. Pellets of 5 urn and I urn size alumina were made at 6000 psig in a single step change. Kinetic runs were made in the temperature range of 673 to 993 K with steam as the oxidant at a flow rate of 9.96E-03 g/cm2 sec. The organics (polymethyl methacrylate, methyl ethyl ketone, methanol) concentration was varied from 5 to 20 by weight%. The oxidation products were analyzed using a Varian 3700 gas chromatograph coupled with CDS 111 integrator, and by volumetric analysis. Carbon analysis was carried out at the IBM Fishkill center using a Leco analyzer. Kinetic rates and activation energies are evaluated. 相似文献
39.
Single crystalline silver nanoparticles have been synthesized by thermal decomposition of silver oxalate in water and in ethylene glycol. Polyvinyl alcohol (PVA) was employed as a capping agent. The particles were spherical in shape with size below 10 nm. The chemical reduction of silver oxalate by PVA was also observed. Increase of the polymer concentration led to a decrease in the size of Ag particles. Ag nanoparticle was not formed in the absence of PVA. Antibacterial activity of the Ag colloid was studied by disc diffusion method. 相似文献
40.
Venkatesh Balasubramanian Kanagasabai Adalarasu Rahul Regulapati 《人机工程学与制造业中的人性因素》2008,18(6):666-677
The purpose of this investigation was to evaluate two different standing postures, intermittent walking (dynamic) and stationary, on 11 volunteers. While performing the activity in a stationary posture, volunteers worked barefoot for 25 minutes at a particular workstation, taking up to five passive breaks. The dynamic standing postural activity was similar in every respect with the exception of the nature of the breaks that were spent walking from one workstation to the other. Foot pressure was analyzed using a static evaluation variable (contact area) and a dynamic evaluation variable (area pressure change root mean square [aPcrms]). Foot center of pressure (COP) was analyzed using two of its features: excursion length (LEN) and root mean square velocity of excursions (VEL). In addition, a psychophysical study was used to distinguish the comfort levels of various muscles between the two postures. The quantifications of the four physiological variables revealed a lower comfort index (p < 0.05) in stationary standing compared to dynamic standing during assembling duties. This significant distinction was further corroborated by the results of the psychophysical test. Such a positive influence of the dynamic standing posture on standing comfort can be used to improve industrial productivity. © 2008 Wiley Periodicals, Inc. 相似文献