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The effects of five polyethylene glycol (PEG) compounds of different molecular weight on the thermal stability of penicillin
G acylase (PGA) obtained from a mutant ofEscherichia coli ATCC 11105 have been investigated. The molecular weights of PEG compounds were 400, 4000, 6000, 10,000, and 15,000. The thermal
inactivation mechanisms of both native and PEG-containing PGA were considered to obey first order inactivation kinetics during
prolonged heat treatments. Optimal concentrations of PEGs at molecular weights of 400,4000, 6000,10,000, and 15,000 were found
to be 250,150,150,100, and 50 mM, respectively. The greatest enhancement of thermostability was observed with PEG 4000 and
PEG 6000, as a nearly 20-fold increase above 50°C. PGA showed almost the same temperature activity profile and optimal temperature
values both in the presence and absence of PEG. The addition of PEGs did not cause any change in the optimal temperature value
of PGA, but the parametersV
m
,K
m
, the activation energy, and thek
cat
values of enzyme were markedly decreased because of the mixed inhibition by PEG compounds. The type of inhibition was found
to be hyperbolic uncompetitive. 相似文献
3.
Altan Kara Perihan Ünak Cenk Selçuki Özlet Akça E. İlker Medine Serhan Sakarya 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):807-813
This research aims to investigate the interaction between phytohemagglutinin-L (PHA-L) and sialic acid, which is abundant on the breast cancer cell (MCF-7) surface and displays monosaccharide characteristics, by experimental and computational methods. Experimentally, CdSe/CdS nanoparticles (QDs) were synthesized; PHA-L was conjugated with QDs and labeled with 125I. Radiolabeling yield was found to be 97 ± 1.2 %. Afterwards, in vitro bioaffinities of radiolabeled PHA-L conjugated QDs have been investigated on MCF-7 cells and it has been observed that the cell incorporation increased with time. The results indicated that 125I labeled QD-PHA-L conjugates represent significant affinity on MCF-7 cells. In the second step of the study, the crystal structure of carbohydrate interaction surface of PHA-L was extracted from the crystal structure of PHA-L. The interactions between this surface and sialic acid were calculated by computational tools. These calculations revealed specific interactions between PHA-L and sialic acid. Semi-empirical methods, PM3 and AM1, were used in these calculations. Significant outcomes have been obtained from the experimental and computational studies and these results demonstrated that PHA-L may be an effective agent for imagining MCF-7 cells. 相似文献
4.
The Ramanujan Journal - Answering a question of Erdös, Komlós proved in 1968 that almost all $$n\times n$$ Bernoulli matrices are nonsingular as $$n\rightarrow \infty $$ . In this paper,... 相似文献
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Bregman H Williams DS Atilla GE Carroll PJ Meggers E 《Journal of the American Chemical Society》2004,126(42):13594-13595
Replacing natural products with kinetically inert metal complexes may lead to a new class of therapeutics in which a metal center plays the role of an innocent bystander, organizing the orientation of the organic ligands in the receptor space. As an example of this approach, a ruthenium complex is described that copies the binding mode of indolocarbazole protein kinase inhibitors and serves as a reversible, low-nanomolar inhibitor for glycogen synthase kinase 3 (GSK-3). 相似文献
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In this paper, the singular second order differential operators are considered defined on the multi-interval. Some boundary and transmission conditions are imposed on the maximal domain functions with the spectral parameter. After constructing the differential operators associated with the boundary value transmission problems on the suitable Hilbert spaces, it is proved that these operators are the maximal dissipative operators. Finally constructing the model operators which are established with the help of the scattering functions, it is proved that all root vectors of the maximal dissipative operators are complete in the Hilbert spaces. 相似文献
9.
Mayté Paredes Zaldivar Norma Galego Fernández Cristina Gastón Peña Manuel Rapado Paneque Sonia Altanés Valentín 《Journal of Thermal Analysis and Calorimetry》2011,106(3):725-730
A new polyacrylic acid/polyhydroxybutyrate semi-interpenetrating polymer network hydrogel, the s-IPN/PAA-PHB, was prepared
by a gamma radiation-induced polymerization. Thermal behavior was studied by thermogravimetric analysis (TG) and Differential
scanning calorimetry (DSC), while the s-IPNs composition, FTIR spectra, and swelling kinetics were also determined. It was
found that the DSC curve showed a melting point which is attributed to polyhydroxybutyrate. The TG curves showed various stages
of degradation which are in correspondence of the presence of crosslinked polyacrylic acid and confirmed the higher thermal
stability of the polymer network. The s-IPN/PAA-PHB composition was 10% of PHB and 90% of PAA. Moreover, the network reached
approximately 600% of swelling in water, so it behaves like a superabsorbent hydrogel. 相似文献
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