Effect of Disulfide Bonds in Human Hair Fibers on the Melting Behavior of Their Crystalline Structure

In the study titled "Effect of disulfide bonds in human hair fibers on the melting behavior of their crystalline structure," researchers Osaki, Okada, Yamamoto, and Joko explored the role of disulfide bonds in the structure of human hair fibers. They specifically examined the relationship between the melting behavior of alpha-crystallites during thermal analysis and the structural orientation of hair fibers when disulfide bonds were oxidized using a 1.5 wt% peracetic acid solution. The study found that oxidative treatment with peracetic acid caused cystine residues to dissociate into cysteic acids, but the alpha-crystalline structure of the oxidized hair fibers was maintained despite the breaking of disulfide bonds. High-pressure differential scanning calorimetry showed that the endothermic peak associated with the melting of alpha-crystallites split into two separate peaks, one melting at a lower temperature and the other at a higher temperature than untreated hair. Additionally, the sum of the areas of these two peaks decreased. Polarized light microscopy revealed that the orientation of intermediate filament-associated proteins (IFAP) persisted even after the orientation of intermediate filaments (IFs) disappeared. These results suggest that some disulfide linkages at the interface between IFs and IFAP dissociated with the peracetic acid treatment, indicating that regions of IFs are stabilized by disulfide bonds and others by hydrophobic interactions for their thermostability.