Keratin composition

The amino acid composition of keratins. Composition of gorgonin, spongin, turtle scutes, and other keratins. J. Biol. Chem., 127, 685 (1939). With D. Bolling. 

Keratin Structure. Keratin is a nonspecific term applied to various insoluble aggregations in hair, nail, skin, and mucosa. Rothberg (33) says of skin,. . what has been called and analyzed as keratin in the past is the total products of epidermal metabolism which are not returned to the metabolic pools but are instead excreted with the cornified epidermal cells. Much has been learned by selective extraction and analysis of these complex products, but the question often arises— what was analyzed Biologists have tried to determine keratin composition by observing synthesis, assembly, and diflFerentiation of the composite parts. 

Flores-Hernandez et al. (2014) studied by DSC the chitosan-starch film and chitosan-starch/keratin composites showed in Fig. 15.15. They observed an endothermic peak that was approximately at 90-100°C, that was associated with loss of water,... 

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. 

The essential genetic material ofthe original vegetative bacterium is retained in the core or protoplast around this lies the thick cortex which contains the murein or peptidoglycan already encountered as a cell wall component (see Fig. 1.2). The outer coats which are protein in composition are distinguished by their high cysteine content. In this respect they resemble keratin, the protein of hair and horn. 

The hair fibers derived from furry mammals are mainly made up (over 80%) of the structural protein keratin. The distinction between wool and hair is not compositional, but related to size wool fibers are generally fine and short, whereas those of hair are usually thicker and longer. The molecule of keratin consists essentially of a combination of amino acids about 18 amino acids make up the keratin molecule (see Textbox 67). The nature of the amino acids, their relative amounts, and their sequence and arrangement within the molecule of keratin vary from one animal species to another but are characteristic of any variety of wool or hair (Asquith 1977) (see Table 89). 

Isotretinoin (Accutane) decreases sebum production, changes sebum composition, inhibits P. acnes growth within follicles, inhibits inflammation, and alters patterns of keratinization within follicles. 

The Formation, Composition, and Properties of the Keratins Wilfred H. Ward and Harold P. Lundgren... 

General formula iGoH OisN Sh. Chemical composition is keratin. 

The amino acid composition of keratin, the protein of hair and wool, includes a greater-than-average proportion of the sulphur-containing amino acid, cystine. Since this is the least soluble of the protein amino acids it can readily be isolated after carefully neutralising an acid hydrolysate of hair (Expt 5.187). Protein hydrolysis is usually effected by boiling for about 10-20 hours with 20 per cent hydrochloric acid. The hydrolysis of hair for the isolation of cystine is, however, best achieved using a mixture of hydrochloric and formic acids. 

Dermal and transdermal delivery requires efficient penetration of compounds through the skin barrier, the bilayer domains of intercellular lipid matrices, and keratin bundles in the stratum corneum (SC). Lipid vesicular systems are a recognized mode of enhanced delivery of drugs into and through the skin. However, it is noteworthy that not every lipid vesicular system has the adequate characteristics to enhance skin membrane permeation. Specially designed lipid vesicles in contrast to classic liposomal compositions could achieve this goal. This chapter describes the structure, main physicochemical characteristics, and mechanism of action of prominent vesicular carriers in this field and reviews reported data on their enhanced delivery performance. 

In 1975, Michaels et al.33 presented a conceptual model of the arrangement of corneocytes and lipids in stratum corneum. They envisaged stratum corneum as a brick and mortar structure with the keratin filled corneocytes as bricks and the intercellular lipids as mortar. This model was further explored by Elias and co-worker.34-37 This model does not per se include a structure-function perspective on the barrier but has had a tremendous impact on the research on stratum corneum and its composition, function, and the regulation of homeostasis. 

From a materials science perspective, the SC is a laminated composite membrane comprised of two distinct domains, specifically, proteins (corneocyte cells with embedded keratin bundles) and lipid bilayers. Corneocyte cells have covalently attached lipids, which makes them compatible with the surrounding lipid matrix. In addition, corneocytes in different layers are held together by protein staples called desmosomes. SC has been designed to exfoliate dead cells in an orderly fashion where the upper layers come off in a layer-by-layer fashion. For this to happen, the desmosomes have to be cleaved by proteolytic enzymes in the SC as the cells approach the outermost layers. 

Although a helices are abundant in proteins, the average length is fairly short, that is, 17 A long containing about 11 amino acids or three turns. Therefore, a helices are typically found in short domains within proteins and not as continuous stretches. Keratins that make up hair and the most superficial layer of skin contain a central domain with an a helical component of 310 amino acids or about 46.5 nm in length. Keratin is an example of a protein with a fairly long a helix. The amino acid composition that favors a helix formation is fairly broad with the exception of proline and serine. 

The composition of keratins. Amino acid composition of hair, wool, horn, and other eukeratins. Ibid., 128, 181 (1939). With cooperation of D. Bolling, F. C. Brand, and A. Schein. 

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