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The 10-nm filaments of baby hamster kidney (BHK-21) cells, when examined either in the form of native filament caps or polymerized in vitro, are long tubes of protein 8--10 nm in diameter. They contain about 42% alpha-helix, which, on the basis of x-ray diffraction data, is arranged in a coiled-coil conformation characteristic of proteins of the alpha type. The known structural properties such as morphology, dimensions, subunit composition, and ultrastructure of this fibrous protein are very similar to those of the mammalian epidermal keratin filament, to which it may therefore be related.
Steinert et al. (Fri,) studied this question.