Quantitation of myosin in muscle

The amount of myosin per gram of cardiac and skeletal muscle was determined in sodium dodecyl sulfate-solubilized tissue homogenates by radioimmunoassay and by isotope dilution. In the rabbit ventricle, there was an average of 27 mg myosin/g wet wt of tissue. In chickens, the myosin content of typical "red" (anterior latissimus dorsi) and "white" (posterior latissimus dorsi) skeletal muscles was higher than that of ventricular muscle, averaging 36 and 48 mg/g of tissue, respectively. The stoichiometry of the heavy and light chains in cardiac myosin was also determined from the quantitative binding of 125I-labeled Coomassie blue to each subunit after separation of the subunits by sodium dodecyl sulfate-gel electrophoresis. With this procedure, we found that the combined light-chain subunits contributed 19% of the myosin mass. After adjustment for the light-chain contribution, the myosin heavy-chain content of the rabbit ventricle averaged 22 mg/g wet wt of tissue.