Figure 2.

Representative size exclusion chromatograms of 140 μM of Aβ in 0.4 M, 2 M, 4 M, and 6 M urea (solid line, from top to bottom). The mobile phase was matched to that of the sample buffer. Molecular weight of Aβ peak was determined by calibration of column at each urea concentration using insulin chain B (3.5 kDa), ubiquitin (8.5 kDa), ribonuclease A (13.7 kDa), ovalbumin (43 kDa), and BSA (67 kDa). The letters M and D represent monomer and dimer, respectively. Arrows represent elution times of ubiquitin at different urea concentrations. The shift in elution times with different urea concentrations in mobile phase is likely due to urea-induced volume expansion. In 4 M urea, dimeric species were observed in four of six replicates; in the remaining two samples, initially only monomer was observed, but there was subsequently complete conversion to dimer within ~2–3 h. In 6 M urea, seven of nine replicates showed a purely monomeric peak initially, shown as a dotted line, followed by a complete switch to purely dimer within ~2–3 h. Only dimer was detected in remaining 2/9 replicates.