Hard keratin IFs

In modem usage, the observed filaments in fiber sections are strictly called hard keratin IFs. Traditionally, these IFs— known as microfibrils—have probably received more intensive study over the years than other fiber stmctural components. The range of the various... 

Parry, D. A. D. (1995). Hard u-keratin IF A structural model lacking a head-lo-lail molecular overlap but having hybrid features characteristic of both epidermal keratin and vimentin IF. Proteins 22, 267-272. 

Solubility of hard keratin proteins may also be lowered markedly with such fiber treatments as mild heating, exposure to sunlight, and mild alkaline solution [206-208], However, extended exposures to the above treatments presumably causes peptide bond cleavage resulting in higher solubilities. Most soluble proteins originate from cortical IF-matrix components, and minor structural components appeared to have lower solubility [34]. 

Epithelial cells express acidic and basic keratins. They associate in a 1 1 ratio to form heterodimers, which assemble into heteropolymeric keratin filaments neither type alone can assemble into a keratin filament. The keratins are the most diverse classes of IF proteins, with a large number of keratin isoforms being expressed. These Isoforms can be divided into two groups about 10 keratins are specific for hard epithelial tissues, which give rise to nails, hair, and wool and about 20, called cytokeratins, are more generally found In the epithelia that line Internal body cavities. Each type of epithelium always expresses a characteristic combination of acidic and basic keratins. 

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