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Morphology and Properties of Hair
Published in Dale H. Johnson, Hair and Hair Care, 2018
Hair fibers form a major component of the outer covering for most mammals. They create a physical barrier between the animal and its environment, and have evolved as a result of their necessary exposure to harsh conditions and the need to be stable over long periods of time to quite severe treatment. All mammalian hairs, together with wools, horns, claws, nails, and quills, mainly consist of a protein material known as α-keratin. As a protein, alpha keratin is a biological polymer consisting of polypeptide chains formed by the condensation of amino acids. In the general formula for a polypeptide chain,
Structure and function of skin
Published in Roger L. McMullen, Antioxidants and the Skin, 2018
In the last two decades, great progress has been made in the elucidation of keratin structure in hair—there are at least fourteen different types of alpha-helical keratins that constitute the crystalline phase of cortical cells in animals.40 It is universally accepted that the great tensile strength of hair is due to the hierarchal organization of the crystalline phase alpha-keratins. While much attention is owed to alpha-keratin, it is intriguing to understand better the important role played by the amorphous matrix, which is believed to be largely composed of proteins belonging to the family of keratin-associated proteins. Also located in the cortex is a cell membrane complex that separates cortical cells from each other and from the overlaying cuticle cells. The cell membrane complex of the cortex is biologically distinct to that of the cuticle, which is discussed in the following.
Antigenic and Cytoarchitectural “Markers” of Differentiation Pathways in Normal and Malignant Colonic Epithelial Cells
Published in Leonard H. Augenlicht, Cell and Molecular Biology of Colon Cancer, 2019
Cytokeratin-type intermediate filaments represent major detergent-resistant cytoskeletal elements the expression and organization of which are regulated in colonic epithelial cells as a function of differentiation and/or transformation.4,29 The cytokeratins are part of (and in fact, comprise the largest subunit grouping) an extensive multigene family of intermediatesized filament proteins. Included in this category are 4 groupings of nonkeratinous polypeptides (vimentin, glial filament proteins, neurofilament polypeptides, and desmin), approximately 20 epithelial cytokeratins, and 8 distinct alpha-keratins of hair-forming cells.153 Filaments constructed of such proteins are “intermediate-sized” (7 to 11 nm in diameter) compared to filaments which comprise the two other major fibrous networks of eukaryotic cells, i.e., the actin-containing microfilaments (6 nm in diameter) and the tubulin-containing microtubules (25 nm in diameter). Under most circumstances, a subset of two to ten keratins is expressed in any particular epithelium with simple epithelia expressing two to four out of a potential set of five, simple epithelial keratins.154 Overall, therefore, the specific composition of epithelial keratins is considerably heterogeneous and can vary significantly according to cell type, phase of embryonic development, cellular growth status, specific disease state, or stage of differentiation/maturation.154-156 The available evidence supports the contention that intermediate filaments are not involved in fundamental cellular housekeeping functions but, instead, participate in specific events related to cell differentiation.153
Occupational exposure assessment with solid substances: choosing a vehicle for in vitro percutaneous absorption experiments
Published in Critical Reviews in Toxicology, 2022
Catherine Champmartin, Lisa Chedik, Fabrice Marquet, Frédéric Cosnier
In addition to effects on water and lipid content, vehicles can also denature intracellular keratin or modify its conformation in the SC, leading to swelling and increased hydration. As previously explained for hydration of the SC, the proteinaceous intracellular region takes up water. At high water levels, the proteins become disordered and water starts competing for hydrogen binding sites on the proteins, decreasing interactions between them (Barry 1987). Water is not the only chemical enhancer that interacts with keratin fibrils. Aprotic solvents such as DMSO and N-methyl-2-pyrrolidone (NMP), some glycols like propylene glycol (PG) and polyethylene glycol (PEG), or anionic surfactants such as SLS also interact with keratin, binding to its positively charged and hydrophobic sites (Morris et al. 2019). This binding potentially disrupts its ordered arrangement (Barry 1987; Moghimipour et al. 2013; Salimi et al. 2015; Haque and Talukder 2018). DMSO interacts with keratins even when present at low concentrations (20%). In addition, SLS causes the alpha keratin filaments to uncoil – denaturing them to produce beta keratin – and thus opens up the polar pathway. As a result, the presence of anionic surfactants in the vehicle enhances water-absorption by the skin. The degree of enhancement depends on the surfactant (Morris et al. 2019).