Table 1.

Kinetic parameters for experimental ThT and NMR elongation data

NMR	cseed = 1 μM	cseed = 2 μM	cseed = 5 μM	cseed = 9.5 μM
y0	0.599 ± 0.001	0.250 ± 0.001	0.086 ± 0.001	0.093 ± 0.001
Aslow	0.333 ± 0.001	0.542 ± 0.001	0.720 ± 0.001	0.32 ± 0.01
Afast	0.084 ± 0.001	0.201 ± 0.001	0.223 ± 0.001	0.65 ± 0.01
kslow/h−1	0.031 ± 0.001	0.032 ± 0.001	0.139 ± 0.001	0.236 ± 0.005
kfast/h−1	0.66 ± 0.02	0.321 ± 0.005	0.739 ± 0.005	0.659 ± 0.008
tmidpoint/ha	13	9.3	3.0	1.1
ThT
y0	1.019 ± 0.002	0.992 ± 0.001	0.987 ± 0.001	0.987 ± 0.001
Aslow	−1.01 ± 0.01	−0.919 ± 0.006	−0.367 ± 0.009	−0.231 ± 0.003
Afast	n.d.	−0.085 ± 0.006	−0.631 ± 0.008	−0.764 ± 0.003
kslow/h−1	0.084 ± 0.001	0.135 ± 0.001	0.156 ± 0.002	0.141 ± 0.002
kfast/h−1	n.d.	0.76 ± 0.09	0.579 ± 0.008	1.08 ± 0.01
tmidpoint/h	8.3	5	2	1

Results of fitting a double exponential function y(t) = y₀ + A_slow exp(–k_slowt) + A_fast exp(–k_fastt) to the experimental data determined by ThT fluorescence and NMR spectroscopy of samples with 100 μM aS monomers and varying concentration of preformed fibers (seeds), at T = 310 K. The midpoints, t_midoint, are plotted in Fig. S3. In Fig. 2, the amplitudes of the two phases are reported as percent of total amplitude. Amplitudes and rate constants for the fast and the low phases are plotted as a function of added seed concentration in Fig. 2. n.d.: not detected.

^aTo determine midpoints of NMR kinetics, the time dependence of integrals obtained in 1D ¹H NMR spectra (Fig. 1 B) were converted into the concentration of aS monomers. Thus, t_midpoint has been obtained at c^aS= 50 μM. To determine the final amount of aS monomers after seeded elongation reactions, samples were spun down, and monomers left in solution were determined by absorption spectroscopy.