Ca2+-sensitive transition in the molecular conformation of molluscan muscle myosins

Filament assemblies of myosin molecules purified from scallop adductor muscles were stabilized by Ca2+ in the presence of ATP or ADP. Electron micrographs showed that the tail part of monomeric myosin molecules was folded in the absence of Ca2+, but was extended in the presence of Ca2+ at physiological ionic strength.