Figure 6.

Photo-excited MB inhibits the Aβ₄₂ aggregation by means of the binding affinity of MB and the photo-oxidation of Aβ₄₂. (a) Change in fluorescence spectra of 0.2 μM MB upon addition of various concentrations of the Aβ₄₂ monomer. (b) Fluorescence binding affinity assay between Aβ₄₂ and MB. The fluorescence of MB (0.2 μM) at 670 nm was measured with increasing concentration of Aβ₄₂ from 0 to 100 μM. Binding constant K_d was derived from the fitted curve. (c) DNPH assay to monitor a carbonyl content in the Aβ₄₂ peptide. DNPH reacts with the carbonyl groups in oxidized peptides, resulting in the formation of a DNP hydrazone product, which shows an absorption maximum of near 380 nm. (d) The kinetics of Aβ₄₂ fibril formation monitored at 30 °C by ThT fluorescence in the absence and presence of MB under dark or light conditions. For the light condition, the MB-treated Aβ₄₂ samples were irradiated with LED light for 30 min at 4 °C before the measurement. Each point is an average of the fluorescence signal of at least four wells containing the same solutions. Lines indicate fits of a sigmoidal growth curve.