Actomyosin content of rabbit heart ventricle

The requirements for quantitative extraction of rabbit cardiac actomyosin were investigated. Extraction of the tissue was carried out at pH 6.5. Under these conditions, precipitation of actomyosin from the soluble tissue extract showed a plateau between pH 6.9 and 7.1. This precipitation zone allowed excellent reproducibility in determination of actomyosin. Precipitation of actomyosin below pH 6.9 resulted in a sharp rise in nonactomyosin protein. The optimum range of ionic strength for quantitative precipitation of actomyosin was 0.03–0.10 (pH 6.9–7.0). The mean cardiac actomyosin content of the ventricles of young growing rabbits was 3.84% of the wet tissue weight and showed little variation among the animals. The cardiac actomyosin content of the ventricles of one dog studied by the same procedure was 5.36%.