In the present study, myoglobin (Mb) and casein were investigated as representative proteins with α-helix-rich and random-coil structures, respectively. Conformational changes of hydrated proteins induced by gradual dehydration were monitored by vibrational circular dichroism (VCD) spectroscopy. In myoglobin and casein, representative α-helix-rich and random-coil proteins, respectively, an increase in left-handed optical activity in the amide I band was detected at the initial stage of dehydration, followed by an increase in opposite right-handed activity in both the amide I and II bands with further dehydration. Because the second step was observed with an increase in the turbidity of the proteins, it can be attributed to their aggregation. In contrast, because the increase in left-handed optical activity is induced by the conformational change of the proteins and is followed by the aggregation, it may derive from the increase in the regularity of the local structure in individual myoglobin or casein that triggers the aggregation.

7As another intermediate structure, an α-helix-rich crystalline Silk I structure was also observed by X-ray scattering 2015 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. Agriculture and Technology, Koganei, Japan We investigated the structural transition from liquid silk to silk fibers with vibrational circular dichroism spectroscopy. Liquid silk showed a major right-handed optically active band at around 1650 cm -1 and a minor one at around 1680 cm -1 . The former disappeared over time, while the intensity in the latter increased. With the former wavenumber, liquid silk mainly adopted a random-coil structure. In contrast, the latter may reflect an intermediate structure in the transition. Furthermore, two right-handed bands at around 1630 and 1660 cm -1 appeared with the disappearance of the major band, and then the wavenumber of the former shifted to around 1620 cm -1 . The shift results from the decrease in the frequency of the CO stretching mode due to the stacking of the β-sheet that comprises fibers. The band at 1660 cm -1 may reflect another intermediate structure due to its strong correlation with that at 1620 cm -1 in terms of their temporal change in intensity.