Infrared absorption spectrum of keratin. II. Deuteration studies

A number of new bands have been found in the spectra of deuterated α- and β-keratin. In particular, the deuteration difference spectrum has been useful for the determination of frequencies of previously unsuspected bands. Thus it is found that the amide A and II frequencies of the nonhelical component in α-keratin occur at 3310–3320 and 1520 cm.^?1, respectively, and that both bands exhibit dichroism consistent with polypeptide chains which have a measure of alignment parallel to the fiber axis. The parallel dichroism of the amide II′ band of this phase at about 1435 cm.^?l also indicates some alignment. A nondichroic residual band at 1513 cm.^?1 in highly deuterated α-keratin is assigned to the tyrosine residue, as a sharp band near this frequency is found in the spectrum of polytyrosine. The ν‖(o) component of the α-helix is weak or absent in α-keratin, and the relatively sharp band observed near this frequency is thought to be due to the tyrosine residue, while its dichroism is caused by the presence of dichroic nonhelical material. A band near 1575 cm.^?1 in deuterated α- and β-keratin is tentatively assigned to the deuterated guanidinium group of arginine. This band becomes progressively more prominent during deuteration, which indicates that some arginine side chains arc slow to exchange, possibly because their environment prevents interaction with D₂O. The deuteration difference spectrum also shows that, contrary to earlier views, helical material in α-keratin exchanges significantly during the early stages of deuteration, although at a slower rate than the nonhelical material, while part of the nonhelical phase does not exchange as rapidly as had been thought and makes a contribution even after many hours or days.