Physicochemical studies have been carried out on tropomyosins isolated by Bailey’s method from the skeletal and heart muscles of the sheep and ox, and from the muscle of fowl gizzard. Equilibrium sedimentation at high ionic strength showed all the tropomyosins to be heterogeneous and the molecular weight concentration plots suggest a system of macromolecules which dissociates on dilution. However the results do not conform to the requirements of a rapidly polymerizing system in that the molecular weights as a function of concentration in the centrifuge cell for different initial concentrations do not overlap to form a continuous smooth curve. The possibility of heterogeneity arising from a slow self-association or the presence of contaminating proteins is discussed. The ultracentrifuge and viscosity results indicate that tropomyosins from the various sources exist in different states of aggregation. High-speed sedimentation equilibrium experiments at high ionic strength indicate that the minimum molecular weight for tropomyosins from all sources is close to the value of 68,000 previously found for rabbit tropomyosin. Molecular weight determinations in 8 m urea gave values about one-half of the minimum found in salt solution. Within the limits of the experimental methods of molecular weight determinations all the tropomyosins consist of subunits similar in mass and identical with the recent figure of 33,500 ± 2,000 reported for rabbit tropomyosin. The homogeneity of the subunits was examined by gel filtration, chromatography on DEAE-cellulose, and gel electrophoresis. Optical rotatory dispersion measurements and ultraviolet absorption data are reported. Quantitative amino acid analyses showed small differences between the tropomyosins, that for fowl gizzard tropomyosin showing the same trends as reported by other investigators for smooth muscle tropomyosins. Proline was absent from fowl gizzard tropomyosin and from a column-purified preparation of rabbit skeletal tropomyosin. The variable proline figures in other tropomyosins may arise from preparation impurities. © 1969, American Chemical Society. All rights reserved.
