Search results for "SUBSTANCES"
showing 10 items of 1122 documents
Detection of Amyloid-β Fibrils Using Track-Etched Nanopores: Effect of Geometry and Crowding
2021
Several neurodegenerative diseases have been linked to proteins or peptides that are prone to aggregate in different brain regions. Aggregation of amyloid-β (Aβ) peptides is recognized as the main cause of Alzheimer's disease (AD) progression, leading to the formation of toxic Aβ oligomers and amyloid fibrils. The molecular mechanism of Aβ aggregation is complex and still not fully understood. Nanopore technology provides a new way to obtain kinetic and morphological aspects of Aβ aggregation at a single-molecule scale without labeling by detecting the electrochemical signal of the peptides when they pass through the hole. Here, we investigate the influence of nanoscale geometry (conical an…
Polymorphism of amyloid-beta fibrils and its effects on human erythrocyte catalase binding.
2009
The Alzheimer's amyloid-beta (Abeta) peptide exists as a number of naturally occurring forms due to differential proteolytic processing of its precursor molecule. Many of the Abeta peptides of different lengths form fibrils in vitro, which often show polymorphisms in the fibril structure. This study presents a TEM based analysis of fibril formation by eighteen different Abeta peptides ranging in length from 5 to 43 amino acids. Spectrophotometric analysis of Congo red binding to the fibrillar material has been assessed and the binding of human erythrocyte catalase (HEC) to Abeta fibrils has also been investigated by TEM. The results show that a diverse range of Abeta peptides form fibrils a…
The kinetic behavior of insulin fibrillation is determined by heterogeneous nucleation pathways
2005
When subjected to acidic conditions and high temperature, insulin is known to produce fibrils that display the common properties of disease amyloids. Thus, clarifying the mechanisms of insulin fibrillation can help the general understanding of amyloidal aggregation. Insulin fibrillation exhibits a very sharp time dependence, with a pronounced lag phase and subsequent explosive growth of amyloidal aggregates. Here we show that the initial stages of this process can be well described by exponential growth of the fibrillated proteins. This indicates that the process is mainly controlled by a secondary nucleation pathway.
Secondary nucleation and accessible surface in insulin amyloid fibril formation.
2008
At low pH insulin is highly prone to self-assembly into amyloid fibrils. The process has been proposed to be affected by the existence of secondary nucleation pathways, in which already formed fibrils are able to catalyze the formation of new fibrils. In this work, we studied the fibrillation process of human insulin in a wide range of protein concentrations. Thioflavin T fluorescence was used for its ability to selectively detect amyloid fibrils, by mechanisms that involve the interaction between the dye and the accessible surface of the fibrils. Our results show that the rate of fibrillation and the Thioflavin T fluorescence intensity saturate at high protein concentration and that, surpr…
Characterization of poly(4-vinylpyridine 1-oxide) by free-solution capillary electrophoresis and micellar electrokinetic chromatography
2008
The migration characteristics of poly(4-vinylpyridine 1-oxide) (PVP-NO) in phosphate buffers of acidic pH (20 mM H 3 PO 4 or NaH 2 PO 4 ) have been studied using both free-solution capillary electrophoresis (FSCE) and MEKC. To inhibit adsorption, 250 mM o-phosphoethanolamine (2-aminoethyl dihydrogen phosphate) was used. In FSCE, PVP-NO showed a narrow peak and a broader band, both having anionic behavior. These peak and band were attributed to the free and aggregated or micellized PVP-NO forms, respectively. According to surface tension measurements, the CMC of SDS in the BGE was 1.8 and 0.48 mM in the absence and in the presence of 1000 μpg/mL PVP-NO, respectively, and the association of t…
Characterization and determination of poly(vinylpyrrolidone) by complexation with an anionic azo-dye and nonequilibrium capillary electrophoresis
2009
Using capillary zone electrophoresis in nonequilibrium conditions, the complexes of poly(vinylpyrrolidone) (PVP) with anionic azo-dyes dissociate following a first-order kinetics. Two peaks due to the remaining PVP-dye complexes and the equilibrium concentration of the free dye, plus an exponential region due to the dye liberated by the complexes during the electrophoretic run, are obtained. This behaviour was closely similar to that described in the literature for protein-probe and DNA-protein mixtures, upon application of the technique known as nonequilibrium capillary electrophoresis of equilibrium mixtures or NECEEM. Using Congo Red and Acid Blue 113, information about the maximal stoic…
Formation of a new cell wall by protoplasts of Candida albicans: effect of papulacandin B, tunicamycin and Nikkomycin.
1987
SUMMARY: Incorporation of polysaccharides into the walls of regenerating protoplasts of Candida albicans was followed in the presence of papulacandin B, tunicamycin and nikkomycin. With the first drug, chitin was incorporated normally whereas incorporation of glucans and mannoproteins was significantly decreased. Tunicamycin decreased incorporation of all wall polymers when added at the beginning of the regeneration process but blocked only mannan and alkali-insoluble glucan incorporation when added after 5 h. Nikkomycin inhibited chitin synthesis, and the walls formed by the protoplasts were enriched in alkali-soluble glucan. Pulse-chase experiments suggested that a precursor-product relat…
C4 Alpha-Chain Reference Typing Report
1990
Previously it was shown that C4A and C4B alpha-chains after separation on SDS-PAGE can provide valuable information on presence and absence, as well as the number of C4A and C4B genes expressed in an individual. All samples submitted for C4 reference typing were also subjected to C4 alpha-chain separation; the results were included in the Final C4 Reference Typing List [Complement Inflamm 1990;7:193-212]. In addition, in selected cases with assumed 'reversed antigenicity', Western blots of C4 alpha-chains with monoclonal anti-C4A and B antibodies were obtained. As a result, subtypic differences of C4B allotypes were detected by the comparison of monoclonal antibodies 1217 and 1228.
Beads of Acryloylated Polyaminoacidic Matrices Containing 5-Fluorouracil for Drug Delivery
2002
Spherical polymeric microparticles have been prepared by a reverse phase suspension polymerization technique. The starting polymer was alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA), partially derivatized with glycidylmethacrylate (GMA). PHEA-GMA copolymer (PHG) was crosslinked in the presence of N,N'-dimethylacrylamide (DMAA) or N,N'-ethylenebisacrylamide (EBA). 5-fluorouracil was incorporated into PHG-DMAA or PHG-EBA beads both during and after the crosslinking process. Swelling studies revealed a high affinity toward aqueous medium, influenced by the presence of 5-fluorouracil. The in vitro release study showed that the release rate depends on the chemical structure of the beads…
Tiliroside and gnaphaliin inhibit human low density lipoprotein oxidation.
2004
Two flavonoids, gnaphaliin and tiliroside, isolated from Helichrysum italicum, were studied in vitro for their capacity to inhibit Cu(2+)-induced human low density lipoprotein (LDL) and diluted plasma oxidation. LDL oxidation was monitored by conjugated diene, thiobarbituric acid-reactive substances (TBARS) formation and electrophoretic mobility on agarose gel. Gnaphaliin and tiliroside increased the lag-phase for diene conjugate production in a dose-dependent manner. The reduction of TBARS production confirmed the antioxidant activity of gnaphaliin and tiliroside with 50% inhibitory concentration (IC(50)) values of 8.0+/-3.9 microM and 7.0+/-2.6 microM respectively. Furthermore, the flavon…