Light-chain movement and regulation in scallop myosin.

Photo-cross-linking techniques show that when scallop myosin or myofibrils are subjected to experimental conditions that cause relaxed muscles to go into rigor, the N-terminal portion of the regulatory light chain of myosin moves towards the essential light chain while the C-terminal portion stays in place. These changes occur on the myosin before combination with actin. Cross-linking of the N-terminal region to the essential light chain in rigor locks the myosin into a conformation such that calcium sensitivity of the actin-activated Mg-ATPase is lost.