Keratin chemical composition

Chemical Composition. From the point of view of leathermaking, hides consist of four broad classes of proteins coUagen, elastin, albumen, and keratin (3). The fats are triglycerides and mixed esters. The hides as received in a taimery contain water and a curing agent. Salt-cured cattie hides contain 40—50% water and 10—20% ordinary salt, NaCl. Surface dirt is usuaUy about 2—5 wt %. Cattie hides have 5—15% fats depending on the breed and source. The balance of the hide is protein (1). 

Wool belongs to the family of proteins (qv) called keratins. However, morphologically the fiber is a composite and each of the components differs in chemical composition. Principally the components are proteinaceous, although wool cleaned of wax, suint, and other extraneous materials acquired during growth contains small amounts of Hpids (stmctural and free), trace elements, and, in colored fibers, pigments called melanin. 

General formula iGoH OisN Sh. Chemical composition is keratin. 

Keratins - ot-Keratins are the major proteins of hair and fingernails and a compose a major fraction of animal skin, oi-keratins are classified in the broad group of intermediate filament proteins, which play important structural roles in nuclei, cytoplasm, and cell surfaces. Their secondary structure is composed predominantly of -helices. Figure 6.11 shows the coiled-coil structure of the ot-keratin in hair. The chemical composition of the cysteine residues in ot-keratin affects its macromolecular structure and function. For example, hair has relatively few cysteine cross-links, whereas fingernails have many such cross-links, / -keratins, on the other hand, contain much more pleated sheet secondary strucure than ot-keratins and are found in feathers and scales. 

When all impurities have been removed, keratin remains. This is prepared in a chemically pure state in the laboratory by extracting dry wool in a soxhiet with ether to remove the oil and fat, and then with alcohol to take away the soaps. The residue is next dried and immersed in warm distilled water to dissolve the suint, after which it is soaked in a 1 per cent solution of hydrochloric acid to decompose any calcium or magnesium soaps which may be present. After rinsing in distilled water the wool is dried and extracted again with ether to remove the fatty acids which have been liberated, and finally rinsed in dilute ammonia till free from acid before drying. Keratin which has been purified in this way has the following average composition. 

Alpha keratin is found in sheep wool. The springy nature of wool is based on its composition of alpha helices that are coiled around and cross-linked to each other through cystine residues. Chemical reduction of the cystine in keratin to form cysteines breaks the cross-links. Subsequent oxidation of the cysteines allows new cross-links to form. This simple chemical reaction sequence is used in beauty shops and home permanent products to restructure the curl of human hair—the reducing agent accounts for the characteristic odor of these products. Beta keratin is found in bird feathers and human fingernails. The more brittle, flat structure of these body parts is determined by beta keratin being composed of beta sheets almost exclusively. 

The composition of protein and lipid in chemically modified keratin fibers was analyzed on silica with chloroform-methanol (80 2, v/v). A rapid immimochromatographic method for the analysis of protein antigens, based tm a sandwich assay format, uses monoclonal antibodies of two distinct specificities, one covalently immobilized to a defined detection zone on a porous membrane, while the other serves as a label. The sample is mixed, and is then passed along the porous membrane by capUlary action, giving a blue color with the antibodies in the detection zone. The detection limit can be below the nanomolar range for the antigen, as in the case of the human chorionic gonadotropin. 

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