Isolation and some properties of a new fiber-forming protein from Tetrahymena pyriformis.

Isolation and characterization of a fibrous protein component which might be associated with contractile ring of a dividing Tetrahymena cell were attempted by making use of coprecipitation of the protein with rabbit skeletal muscle myosin. The protein was purified to homogeneity by ammonium sulfate fractionation between 40--70% saturation and column chromatography of Sephadex G-200, starting from KCl-extract of Tetrahymena acetone powder. Its molecular weight was calculated to be 38,000, based on the electrophoretic mobility in sodium dodecyl sulfate (SDS)-polyacrylamide gel, whereas molecular weight of its native state was determined to be 140,000 by gel filtration on Sephadex G-200, and its sedimentation coefficient was about 9S as estimated by sucrose density gradient centrifugation. The latter was a particle of 7.7 nm in diameter under an electron microscope and supposed to be a tetramer of the 38,000-dalton protein. The protein is considered to be a new, unique protein, since it is definitely different from the ubiquitous non-muscle actin in molecular weight, polymerizability in KCl solution and amino acid composition, and it also different from tropomyosin and tubulin in immunological characteristics and amino acid composition.