Amyloid β-protein aggregation produces highly reproducible kinetic data and occurs by a two-phase process

Protein aggregation can lead to major disturbances of cellular processes and is associated with several diseases. We report kinetic and equilibrium data by ThT fluorescence and enzyme-linked immunosorbent assay of sufficient quality and reproducibility to form a basis for mechanistic understanding of amyloid β-peptide (Aβ) fibril formation. Starting from monomeric peptide in a pure buffer system without cosolvents, we find that the kinetics of Aβ aggregation vary strongly with peptide concentration in a highly predictablemanner. The free Aβ concentration in equilibrium with fibrils was found to vary with total peptide concentration in a manner expected for a two-phase system. The free versus total Aβ concentrationwas linear up to ca. 0.2 μM, after which free Aβ decreased with total Aβ toward an asymptotic value. Our results imply that Aβ fibril formation arises from a sequence of events in a highly predictable manner.