Dissociation of Pi

Actin absence: The dissociation of Pi is very slow. Actin addition: raises the rate of Pi dissociation 300 fold to approximately 10 ATP molecules per myosin per sec . The dissociation of Pi also induces the “power stroke” for myosin action. The release of Pi causes small conformational changes in the head (motor) domain. This is amplified by a “converter” region at the base of the head which acts as a fulcrum to cause the leverlike neck to rotate. This in turn is amplified by the rodlike lever arm, which constitutes the neck domain, so the actin filament moves by a few nanometers.