Keratin fibers

The homy layer consists of about 10% extracellular components such as lipids, proteins, and mucopolysaccharides. Around 5% of the protein and lipids form the cell wall. The majority of the remainder is present in the highly organized cell contents, predominantly as keratin fibers, which are generally assigned an a-helical structure. They are embedded in a sulphur-rich amorphous matrix, enclosed by lipids that probably he perpendicular to the protein axis. Since the stratum comeum is able to take up considerably more water than the amount that corresponds to its volume, it is assumed that this absorbed fluid volume is mainly located in the region of these keratin structures. 

Alpenfels and coworkers studied the hydrolysis of glycoproteins and keratin fibers with 1 or 2 M hydrochloric acid for various periods of time at 100°. These investigators found that the concentration of neutral monosaccharides from hard keratin reached a maximum after hydrolysis with 2 M hydrochloric acid for 2 h at 100°, and the yield of the neutral monosaccharides was linear up to 25 mg of hair per mL of hydrochloric acid solution. The latter fact shows that a relatively large amount of protein does not interfere with the analysis of a relatively small amount of carbohydrate. 

Keratin filaments are visible here in an epithelial cell. Keratin fibers belong to the group of intermediate filaments (see pp. 70, 204 d = nucleus). 

The hair matrix possesses a large monitoring window (months/years) that allows a retrospective analysis and the study of past history. Hair is also characterized by a high stability and a minimum possibility of adulteration [41, 42], The structure of the hair can be considered as a repeated network of keratin fibers. There are also melanins, lipids, and all the compounds of cells that led to the formation of the stem. The growth of hair is in the range of 0.6-1.4 cm/month [43,44],... 

The general mechanisms by which the NMF components influence SC functionality have been studied extensively. From a physical chemistry perspective the specific ionic interaction between keratin and NMF, accompanied by a decreased mobility of water, leads to a reduction of intermolecular forces between the keratin fibers and increased elastic behavior. Recent studies have emphasized that it is the neutral and basic FAA36 in particular that are important for helping keratin acquire and maintain its elastic properties. Consistent with these observations Sakai et al.37 reported that the ratio of acidic amino acids to total amino acids correlated to the resonant frequency a measure of skin stiffness. 

A furylmethyl group has been incorporated into a dye developer-coupler combination which has been shown to be useful for the oxidative dyeing of keratin fibers, especially human hair <2002W02072568>. The regioisomeric furans 29 and 30 belong to this class of compounds and are easily synthesized from the corresponding aldehydes and a previously generated aminophenyl carbamate. 

Fibrous protein structure investigations applying X-ray diffraction and electron microscopy were reviewed by Blakely (31). Keratin fibers are made of three main structural components the cuticle, the cortex, and the medulla. The medulla is only present in coarse fibers. The cortex forms the bulk of the fiber. Various morphological models have been proposed to explain the mechanical properties of keratin fibers. It is generally agreed that the cortex consists of fibrils in which protein molecules exist in helical and nonhelical regions. 

The ability of keratin fibers to assume a more or less permanent change in shape or length when steamed under stress has been exploited in the clothing and hairdressing trades for centuries. The term setting is used to describe this property. 

Hence the changes which take place during supercontraction of keratin fibers are similar to those occurring when collagen or aligned crystalline polymers are converted to their elastomeric form (Mandelkern, 1959). 

C. Effects of Chemical Modification on Physical Properties of Keratin Fibers... 

Fiq. 20. Relationship between supereontraction of keratin fibers and time of treatment in SAM LiBr at 89°C (Haly and Feughelman, 1957). 

The curves relating residual disulfide of /S-methylated fibers and strain at the end of the yield region are identical within experimental error for a number of different keratin fibers. This suggests that disulfide bonds in both high-sulfur and low-sulfur proteins contribute to the properties of the fiber in the post-yield region. 

Most of the filaments in basal cells lie perpendicular to the skin surface, but in the stratum spinosum they gradually shift into a perinuclear network (31, 64). The above concept is diagrammed in Figure 10. As cells become fiattened, the radial pattern of filaments about the nucleus (31, 34) is preserved but the keratinized fibers come to lie parallel with the skin surface, like spokes in a bicycle wheel (31, 64). Collapse of the fibrous cage produces tension on desmosomes and deforms the cell envelope so that, the deep interdigitations formed between... 

---