Hair keratin is a composite structure in which intermediate filaments (IF) are 
embedded in a protein matrix. During the early stages of development in the hair 
follicle the redox potential is such that the cysteine residues in the IF are 
maintained in a reduced form. However, at a late stage of development the redox 
potential changes to produce an oxidizing environment and the IF undergo a 
structural transition involving both molecular slippage and radial compaction. 
In our earlier study the changes in the molecular parameters were estimated from 
knowledge of the sites of artificially induced crosslinks, and it was noted that 
the changes in these parameters realigned many of the cysteine residues to 
positions more favorable to disulfide bond formation. As the energy involved in 
the formation of disulfide bonds is much greater than that of hydrogen bonds or 
van der Waals interactions the structural transition is likely to be dominated 
by the requirement that the bonded cysteine residues occur at closely equivalent 
axial positions. This criterion was used in the present study to obtain more 
precise values for the molecular parameters in the oxidized fiber than has 
hitherto been possible. A comparison of the sequences of hair keratins and 
epidermal keratins suggests that the slippage observed in trichocyte IF during 
keratinization does not occur in epidermal IF.