The localization of myosin and paramyosin in the myofilaments of the byssus retractor muscle of Mytilus edulis

Glycerinated fibers of the byssus retractor muscle of Mytilus edulis were extracted under various conditions of pH and ionic strength. The results indicate that in the myofilaments, the myosin forms an outer layer of fine filaments surrounding the paramyosin core. Consequently, only after removing the myosin could the paramyosin be extracted. After extraction of myosin and paramyosin, a periodic “beaded” structure of 740 A spacing was left in place of the myofilaments. These “beads” resisted extraction in everything but 8 M urea. It is not known at this point what the nature and function of this structure is.