Myosin binds actin in this extended conformation ... required for the contraction of muscle cells. ATP supplies the energy, as described above, but what does calcium do? Calcium is required ...

The authors point out that, in low concentrations of ATP, when the myosin heads both remain bound to the actin filament ... cross-bridge model of muscle contraction proposed in 1969.

These highly efficient and specialized proteins are responsible for a wide range of essential cellular processes, including muscle contraction ... domain contains the catalytic site for ATP hydrolysis ...