Isolation and partial characterization of intermediate filament protein (skeletin) from cow heart Purkinje fibres.

The intermediate filament protein skeletin from cow heart Purkinje fibres was purified to homogeneity by a selective extraction procedure and gel chromatography in the presence of sodium dodecyl sulphate. Monospecific antibodies were obtained by immunisation of rabbits with the sodium dodecyl sulphate-skeletin complex, and rocket electrophoresis made it possible to quantify the concentration of protein. The skeletin monomer has a molecular weight of 55 000. Amino acid analysis revealed that skeletin has a high content of glutamic acid, aspartic acid, alanine and leucine, together constituting more than 50% of the molecule. The isoelectric point is determined as 6.35. Skeletin is insoluble at pH 4--6 in the absence of detergent and shows increasing solubility at higher and lower pH. The biochemical characteristics are discussed in relation to the cytoskeletal function of the filaments. Comparison with intermediate-sized filament protein of other tissues show certain important similarities suggesting that the filaments may share a common evolutionary ancestry.