A comparative study of tropomyosin from vertebrate ventricles

A comparative study of vertebrate ventricle tropomyosin has been carried out from the viewpoint of molecular evolution. The ventricles containing one-component tropomyosin were generally known, and in this paper those containing two components were also found in 8 species among mammals, reptiles, amphibia, and fish, but not among birds. The two components were concluded to be authentic tropomyosin and not artifacts since they showed lower electrophoretic mobilities in the presence of urea, and they were precipitated at pH 4.5 and bound to F-actin. Studies on cysteine contents and cyanogen bromide cleavage peptide patterns revealed that the characteristics of the two tropomyosin components from pig, turtle, amphibia and carp ventricles varied increasingly in that order from typical alpha- and beta-characteristics as seen in rabbit skeletal muscle tropomyosin. The single component of chicken ventricle tropomyosin showed alpha component characteristics in its electrophoretic mobility and cysteine content, and beta component characteristics in cyanogen bromide cleavage peptide pattern. The two components of carp ventricle tropomyosin seemed to be the most primitive, having two cysteine residues per molecule and a cyanogen bromide cleavage peptide pattern different from those of the two components of rabbit skeletal muscle.