Comparison of 10 nm filaments from three bovine tissues

Enriched fractions of 10 nm filaments were isolated from three bovine tissues and were compared using morphological biochemical, and immunological techniques. We studied keratin filaments from hoof epidermis, 10 nm filaments from corneal epithelium, and 10 nm filaments from brain white matter. The parameters of comparison and results were as follows.

1. 1. Corneal epithelial filaments and keratin filaments repolymerized after a buffered 8 M urea extract of the tissue was dialyzed against a low ionic strength (0.005 M) buffer. However, a greater yield of repolymerized corneal epithelial filaments was obtained if the urea-soluble fraction was dialyzed against the same buffer containing 0.17 M NaCl. Brain filaments harvested by cell fractionation did not repolymerize when similarly treated.

2. 2. Electrophoretic patterns of proteins of filament-enriched fractions from the three sources were different in sodium dodecyl sulphate (SDS) polyacrylamide gels, except for one co-migrating band.

3. 3. Peptide mapping by limited proteolysis of the eluted co-migrating proteins showed few similarities.

4. 4. Amino acid analysis of the co-migrating proteins revealed numerous differences.

5. 5. Antibodies to the co-migrating corneal epithelial filament and brain filament proteins reacted only with their own antigen and whole filament type, and antibody to total keratin filament protein cross-reacted only with keratin filaments.