Lever-arm motion. Two forms of the S1 fragment of scallop-muscle myosin. Notice the dramatic conformational changes when the identity of the bound nucleotide changes from the ADP–VO43− complex (A) to the nucleotide-free form (B) or vice versa, including a nearly 90-degree reorientation of the lever arm.
[Drawn from 1DFL.pdb and 1SR6.pdb.]