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 beta-peptide (A beta) fibril formation. Starting from monomeric peptide in a pure buffer system without cosolvents, we find that the kinetics of A beta aggregation vary strongly with peptide concentration in a highly predictable manner. The free A beta 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 A beta concentration was linear up to ca. 0.2,mu M, after which free A beta decreased with total A beta toward an asymptotic value. Our results imply that A beta fibril formation arises from a sequence of events in a highly predictable manner.