The resulting kinetics of the parallel β-sheet fractions (fpara; Figure ) show that initially a 1:1 mixture of parallel and antiparallel β-sheets is adopted in both cases, the tMLM and the tBLM systems. However, while the fraction does not change on tMLMs, on tBLMs the fraction of parallel β-sheets increases suddenly after 1 h towards 100% parallel β-sheets. Sigmoidal shaped kinetics typically occur for cooperative or autocatalytic mechanisms, and we have observed such cases previously during investigations of antimicrobial peptides. For instance, when investigating the ion channel-forming alamethicin, we observed that monomeric species that bind initially had to overcome a threshold in surface density. This delayed the oligomerization and incorporation of alamethicin as transmembrane ion channels. Similarly, the transmembrane penetration of the ionophore enniatin followed a mechanism where a slow spontaneous incorporation was followed by an autocatalytic burst mediated by already incorporated species. In both cases, the temporal delay was on a similar order as observed herein. As such, our data implies that transmembrane-incorporated Aβ structures have a cooperative and/or autocatalytic effect towards the formation of parallel βsheets, but this is not the case for species adsorbed on the membrane interface.