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CROSS-BRIDGE FORMATION
(THE "ATTACH" STAGE)
When available, a Ca2+
ion binds to the troponin complex, which causes
the troponin to change shape. This change in shape
displaces the attached tropomyosin protein, exposing
the active site.
Myosin is an ATPase that catalyzes
the hydrolysis of the ATP into a molecule each
of ADP and Pi. The hydrolysis of the
ATP causes the myosin head to bend/flex about
45 degrees into its "cocked" position.
The myosin head then binds to
the exposed active site on the actin molecule,
forming a cross bridge.
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