Structural changes in myosin in dystrophic, denervated and regenerating muscle in mice

Abstract The technique of sodium dodecyl sulphate-polyacrylamide gel electrophoresis was used to resolve the large and small polypeptide chains of mouse myosin and to determine their molecular weights. In myosin preparations from dystrophic, denervated and regenerating muscle a decrease in amount of the large sub-unit (molecular weight 200,000) was accompanied by an increase in smaller protein chains. There was evidence that some of the smaller chains in dystrophic myosin were due to proteolytic activity. These smaller chains repeatedly co-precipitated with myosin at low ionic strength and were not removed by gel filtration through Sephadex G-200, indicating that they were tightly bound to the myosin molecule. Normal myosin contained three low molecular weight proteins (26,500, 19,000 and 16,500). The 19,000 molecular weight protein was not detectable in myosin preparations from denervated muscle, regenerating muscle and normal muscle treated with extraction medium previously used to extract dystrophic muscle, but Ca 2+ -activated ATPase was unaffected. In dystrophic myosin both the 19,000 and 16,500 molecular weight proteins were undetectable and the level of Ca 2+ -ATPase was reduced.