Absence of phosphates from the myosin heavy chains of striated muscles

This work aimed to determine whether the heavy chains of myosin from different striated muscle were phosphorylated. Myosin and its heavy chains were prepared from cardiac and skeletal muscles of rats injected in vivo with radioactive phosphates. The results for radioactive phosphate localization indicate the absence of phosphate from pure heavy chains and from any of their purified fragments, whatever the striated muscle used. In addition, phosphates are present in the myosin phosphorylated light chain and in a contaminating protein closely associated to the myosin heavy chain.