Abstract
First, we quantitatively determined the ultrasonic power using both calorimetry and KI oxidation.
Under the properly calibrated ultrasonic power, we investigated the ultasonication-induced amyloid formation
process of mouse prion protein (mPrP). Intriguingly, the nucleation time of the amyloid fibrils was found to be
shortened almost proportionally to the ultrasonic power, indicating that the probability of the occurrence of
nucleus formation increases proportionally to the ultrasonic power. While at the strong ultrasonic power larger
than 2.0 W, amyloid fibrils were formed early, but simultaneously fine fragmentation of fibrils occurred.
Subsequently, we examined the aggregate reaction during continuous horn-type ultrasonication. During
continuous ultrasonication, the mPrP aggregation was observed to have rapidly occurred within 1 h. Electron
microscopy revealed that twisted fibrils, β-oligomers and amorphous aggregates were formed at pH 2.2, 4.0
and 9.1, respectively. Under the same conditions, hen egg white lysozyme also aggregated readily. We found
that these phenomena could be sufficiently explained by assuming a narrow reaction field around the
cavitation bubbles formed during the ultrasonication. These cavitation bubbles may act as catalysts that
decrease the activation free-energy that leads to aggregate formation.
