K-3-rh inhibits polymerization, fibril extension and secondary structural transformation of Aβ42. A. Inhibition of Aβ42 polymerization. Aβ42 (20 μM) was incubated in PBS at 37°C in the presence of 0 (open circle), 5 (closed circle), 10 (open triangle), 20 (closed triangle), 40 (open square) and 50 (closed square) μM K-3-rh for 0–6 h. IC50 was calculated as 30 μM. B. Logarithmic plot of F(t)/A−F(t) versus reaction time obtained from polymerization assay. C. Inhibition of Aβ42 fibril extension. Fresh Aβ42 (20 μM) was added to 1.1 μM preformed seed and incubated at 37°C in the presence of 0 (open circle), 10 (open triangle), 20 (closed triangle), and 40 (closed square) μM K-3-rh. IC50 value was calculated as 20 μM. D. Logarithmic plot of A−F(t) versus reaction time obtained from the fibril extension assay. E. Effect of Aβ42 concentrations on the initial rate of Aβ42 fibril extension. F. Inhibition of β-sheet transformation of Aβ42. The peptide (20 μM) alone or in the presence of K-3-rh (40 μM) was incubated in PBS at 37°C for 0 or 12 h as indicated. Spectra were obtained by subtracting buffer background as described in Materials and Methods section.