Myosin is a protein that binds to F-actin and has ATPase activity that is activated by F-actin. Myosin II heavy chain is two-headed. It self-assembles into filaments. Hexamer of 2 heavy chain subunits (MHC), 2 alkali light chain subunits (MLC) and 2 regulatory light chain subunits (MLC-2). The rodlike tail sequence is highly repetitive, showing cycles of a 28-residue repeat pattern composed of 4 heptapeptides, characteristic of alpha-helical structures. This region is interrupted by a hinge and joined by a nonhelical tailpiece where the regulatory phosphorylation sites reside. The hinge region may play a key role in mediating the effect of heavy chain phosphorylation on enzymatic activity. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family.