I am wondering what really powers the myosin head to undergo the power stroke to push the actin filaments towards the M-line. I have 2 thoughts:
when ATP in the myosin head gets hydrolyzed, the energy released is stored in the head. This energy powers for the power stroke.
when ATP is hydrolyzed, inorganic phosphate and ADP leave accordingly (90deg--> 50deg --> 45deg), the conformational changes of myosin head proteins cause the power stroke.
I think (2) is more plausible as the order of actions (moving actin filaments by 6.7nm + 1.3nm in order) is more 'conventional'(wiki), rather than a single action (using energy by ATP hydrolysis, a 1-step boost of energy).
However, if (2) is really correct, then may I ask what is the energy released in (1) used for in the myosin head, does it just simply fade away as heat energy?
thank you very much.