Motors in muscle: the function of conventional myosin II

Solution measurements indicate that actin and myosin alternately bind and dissociate during one ATP hydrolysis cycle. Crystallographic studies indicate at least two basic conformations of the myosin head exist in which the regulatory domain swings through an angle of about 70 degrees. Actin must further modulate these conformations, but high-resolution information about the actomyosin interface is lacking. One-to-one coupling between the ATPase cycle and a mechanical cycle involving myosin-head bending could account for about a 10 nm stroke size. At high sliding velocities, discrepancies remain which suggest that a myosin head may undergo repetitive interactions with actin for each ATP hydrolysed.