Keratin molecular composition

Table IL Amino Acid Composition of Wool Keratin (Molecular Weight 68,000 kD) (18,19)...

The keratins are a specialized group of structural fibrous proteins that are characterized by their high cystine content and can be classified according to the amount of sulfur present in the protein. Structures such as wool, hair, hooves, horns, claws, beaks and feathers are classified as hard keratins because the sulfur concentration in these proteins is greater than 3%. Keratin proteins containing less than 3% sulfur, such as the stratum corneum (the outermost layer of skin), are classified as soft keratins. Although these keratin proteins have a similar molecular composition major spectral differences have been observed in the intensities of the C-S and S-S stretching vibrations the conformation of the disulfide bond and the position, line shape and bandwidth of vibrations associated with the proteins secondary structure. 

Characterization of the keratinized cells by classical histological and biochemical approaches has been difficult because of the intractable nature of the tissue. Yet it is precisely these properties of mechanical strength, insolubility, macromolecular character, and lack of metabolic activity along with its ease of isolation which makes stratum corneum amenable to analysis by physical methods. The extreme complexity of composition, molecular structure, and organization of stratum corneum make interpretation of these macroscopic properties in terms of molecular structure and events dependent heavily on analogous studies of model synthetic polymer systems and the more thoroughly characterized, keratin-containing wool. 

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