FIG. 4.

Initial rates of aggregation of Aβ40 monomers into filaments in the presence of 21 µM seeds; initial monomer concentrations ranging from 3.5 µM to 70 µM. Data taken from Ref. 10. The initial rates in the presence of such high seeds should depend only on the elongation rate; if saturation effects are present in the elongation reaction, the initial aggregation should have a sublinear dependence on initial monomer concentration [see the cyan curve in Fig. 2(a)]. Instead, an approximately linear dependence on the monomer concentration is observed, demonstrating the absence of significant saturation in elongation at the monomer concentrations studied. This supports the tentative conclusion from Fig. 3 that the saturation effects additional to those from secondary nucleation, visible at the upper end of the concentration range studied, originate from primary nucleation and not from elongation.