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Effects of trace elements in polymerization of keratin proteins and destruction of the filaments by processing techniques for electron microscopy.

Keratin extracted from keratinized cells of newborn rats polymerizes into filaments in vitro and this polymerization has been shown to be greatly stimulated by addition of divalent cations. In this study we investigated the optimum conditions for filament formation by use of CaCl2, ZnCl2, and GdCl3, a trivalent lanthanide. It was found that a concentration about 10 times higher was required for elongation and formation of wider filaments with CaCl2 when compared with that for ZnCl2, GdCl3 caused enhanced polymerization with an even lower concentration. Effects of fixation(s) and other processing techniques used for routine electron microscopy on the polymerized keratin filaments were also examined by electron microscopy and SDS polyacrylamide gel electrophoresis. Degradation of keratin protein was detected in various steps involved in handling of the keratin filaments. These results indicate that ultrastructural studies of keratin in epidermal cells in situ may be improved by re-evaluation of presently used experimental procedures.