Keratin reduction

Keratinization Reduction in the production of mucus of epithelial cells, particularly in the conjunctiva and cornea of the eye due to vitamin A or retinol deficiency. 

The differences in the amino acid chemistry of the hide coUagen and the hair keratin are the basis of the lime-sulfide unhairing system. Hair contains the amino acid cystine. This sulfur-containing amino acid cross-links the polypeptide chains of mature hair proteins. In modem production of bovine leathers the quantity of sulfide, as Na2S or NaSH, is normally 2—4% based on the weight of the hides. The lime is essentially an unhmited supply of alkah buffered to pH 12—12.5. The sulfide breaks the polypeptide S—S cross-links by reduction. Unhairing without sulfide may take several days or weeks. The keratin can be easily hydrolyzed once there is a breakdown in the hair fiber stmcture and the hair can be removed mechanically. The coUagen hydrolysis is not affected by the presence of the sulfides (1—4,7). 

Similar keratin filaments are found in hair. In a single wool fiber with a diameter of about 20 pm, millions of filaments are bundled together within dead cells. The individual keratin helices are cross-linked and stabilized by numerous disulfide bonds (see p. 72). This fact is exploited in the perming of hair. Initially, the disulfide bonds of hair keratin are disrupted by reduction with thiol compounds (see p. 8). The hair is then styled in the desired shape and heat-dried. In the process, new disulfide bonds are formed by oxidation, which maintain the hairstyle for some time. 

In the tanning process hides are first washed or soaked, hair and keratinous debris are removed, bated (enzymes are used to break down non-collagenous components, which are washed out) and the hide is acid-pickled to prepare for the addition of the chromium salt. Contemporary processes are exclusively based on one-bath procedures and utilize chromium(III). The older two-bath process is now obsolete, mainly because it involved the in situ reduction of chromate, a major environmental and toxicological hazard (cf. chromate toxicity p. 947) to chromium(III) on the hide. A useful review of the history of chromium tannage processes is available.1205... 

The intestinal mucosa shows a reduction in the number of goblet cells without keratinization. Alterations in intestinal epithelium and metaplasia of pancreatic ductal epithelium are common. They may be responsible for the diarrhea occasionally seen in vitamin A deficiency. 

Sulfitolysis occurs simultaneously with Keratin denatured through direct reduction... 

A weakening of the binding forces between the keratinized epithelium and the layer of grease via the reduction of the surface tension between the water and the water-resistant oil/grease. Because of this reduced surface tension, water (and surfactant molecules) can penetrate into the finest wrinkles of the skin. In this way, more and more interface is occupied by surfactant, and the adhesiveness of the soil-containing layer is further weakened, a process facilitated by mechanical rubbing. 

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. 

Reduction in the water holding capacity of the corneum can also make the corneocyte proteins brittle and vulnerable to cracking. Keratins in the corneum have a glass transition temperature just below the body temperature28 and this is sensitive to humidity levels. Glass transition temperature is the point below which the material is brittle. As the humidity/water content of the SC decreases, glass transition temperature increases to values above the body temperature thus making the corneocytes brittle at body temperature. 

Reduction in Neutral Solution. Several methods have been described for extracting protein from keratins following reduction in neutral solution. Urea-thioglycolate was used for this purpose by Jones and Mecham (1943-1944) when comparing the proteins from a variety of keratins. Thompson and O Donnell (1962b) reduced wool proteins in neutral solution and then... 

Reduction of the disulfide bonds of keratin has been much studied not only because of its use for preparation of soluble derivatives (Section... 

II, A,1), but also because it is the basis of some setting methods (Section VI,A,2). To the chemist interested in solubilizing keratins for fractionation studies the major concern is to achieve complete and specific reduction of the cystine. 

An interesting aspect is that moths only thrive on keratin which contains disulphide bonds. If these are ruptured by reduction with sodium hydrosulphite and thioglycoUic acid and new links are built by methods such as joining primary amino groups with glyoxal, the wool is immune from attack by moths. 

The major producers of this amino acid are presently Chinese companies. The usual production process is the extraction of the dimer form cystine from keratin hydrolysates, mainly human hair, and the electrochemical reduction to cysteine. As the raw material human hair is not well accepted by the end consumer, especially not by vegetarian people, there is a big demand for alternative production processes. One company succeeded in a synthetic route to produce cysteine, but this route is quite expensive. In addition to that synthetic starting materials are not really the favorites in the food industry. Attempts to establish a fermentation process as common for other amino acids, like glutamate or lysine, have failed so far. 

Microemulsions have also been investigated for the use in chemical hair treatment [14]. Permanent wave products are based on the reduction of hair keratine cystine, which weakens the protein structure and allows a manipulation of the hair shape. Savelli et al. compared the cystine reduction obtained by thioglycolic acid in water with that obtained by a microemulsion. The microemulsion is based on the anionic surfactant sodium dode-cylsulphate, the co-surfactant pentanol and dodecane as the unpolar oil component. The cysteine formation is evaluated over a time period of 5 min. The experimental data are... 

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