The data highlights a distinctive feature of Φ-value analysis of fibril growth, namely its concentration dependence. While protein folding is generally a unimolecular process and Φ-values are concentration-independent, for a bi-molecular reaction, such as fibril growth, they will depend on concentration. This is because the forward reaction, i.e. fibril growth, depends on monomer concentration, whereas the back-reaction, i.e. fibril dissociation, does not. The ∆∆G ‡-U values are derived from the relative elongation rates (Table ) that were measured by QCM, as the slope of the third overtone frequency during incubation of a sensor with immobilized WT fibrils with variant monomer concentrations of 5 and 20 µM. Each elongation rate is normalized to a WT injection prior to variant injections. The ∆∆G A-U values were obtained from a global fit to all chemical depolymerization data sets, including several WT references (Table ).