ABSTRACT
KERATINS are proteins found in hair, wool, feathers, nail, horns, and other ep-ithelial coverings (MacLaren and Milligan, 1981; Feughelman, 1985; Fraser et al., 1986; Husken, 1986; Heid et al., 1986). In wool, keratins are main constituents of long cortical cells (Figure 10.1) and weigh 30-60% of the total fiber. Keratins are distinguished from collagen, silk fibroin, and other structural proteins by their high content of cysteine and half-cystine residues (7-20 mol% of all amino acid residues). The ratio of cysteine to half-cystine in wool is about 0.2 to 0.8 (Arai et al., 1996). Because the aforementioned biological materials are constructed from keratins interconnected three-dimensionally through cystine disulfide (S-S) bonds, they may be disassembled into basic fragments by chemically reducing S-S bonds to sulfhydryl (SH) groups (of cysteine residues). Then, SH groups in the blocks may be re-associated by oxidative S-S bond formation to produce new polymeric proteinaceous materials, which may be useful as biomaterials. This recycling reduction/oxidation approach is not feasible with proteins, such as collagen and silk fibroin, that lack cysteine and cystine residues. Here, we discuss keratin films produced by oxidation of a reduced form of keratins (referred to hereafter as “reduced keratins”). This chapter deals mainly with the preparation and characteristics of the reduced keratins and the properties and potential uses of their films.
