Kinetics and thermodynamics studies of β-amyloid peptide aggregation in aqueous solutionKinetics and thermodynamics studies of β-amyloid peptide aggregation in aqueous solution
| Autor: | Hui-Ting Tsai, 蔡蕙婷 |
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| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 In this study, we investigated the aggregation of Aβ（1-40） in various conditions including different incubated temperature、salt concentration and pH. The objectives of this investigation went in two fold and were achieved by the following studies : First, we used Circular Dichroism (CD) to observe the secondary structure transition during Aß aggregation, and we used Thioflavine T（ThT）fluorescence probe and AFM to monitor the fibrils’ formation and morphology. Second, we use Isothermal Titration Microcalorimetry (ITC) to obtain the dilution heat at different Aß aggregate states. The thermodynamic information during Aβ aggregation was then discussed with the CD and fluorescence data. The variations of secondary structure of Aβ（1-40） obtained by CD exhibite a temperature and salt concentration dependent behavior. The transition from random coil to ß-sheet can be described by a two-state model. It indicates that the hydrophobic interactions is important for the intermolecular ß-sheet structure stability of Aβ（1-40） in solution. Besides, from the time dependent CD spectrum fitting, we found that the rate constant of nucleation is much smaller than that of elongation in the process of aggregation of Aβ（1-40）, indicating nucleation is the rate-determining step. From thermodynamic analysis, the dilution heat（ΔHdil） of Aß(1-40) monomer obtained by ITC is an endothermic reaction, and as temperature increases, the ΔHdil increases. The results demonstrate that hydrophobic interactions play a central role in the nucleation process of Aß(1-40). Moreover, we also observed that the mechanism of Aβ（1-40）aggregation in various salt concentration is different. In low salt concentration, monomer deposition is only on the ends of fibrils and resultes in long and thin fibrils. In contrast, monomer and fibril and fibril and fibril association occures in high salt concentration due to the reduced electrostatic repulsive forces, and the association involves lateral interactions resultes in short and thick fibrils. These results were demonstrated by AFM observation. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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