Breaking down of ATP or of the ATP returns the myosin molecule to the high energy conformation.

Hydrolysis

Explanation:

Actin is a protein that forms thin filaments which are part of the contractile apparatus in muscle cells. In these cells contraction is triggered by the interaction between actin filaments and myosin filaments that produces their movement relative to one another, a process that requires adenosine triphosphate (ATP). In the first place, myosin-ATP binding causes myosin heads to release actin. Subsequently, ATP hydrolysis induces a conformational change in the myosin filament, thereby myosin 'walks on the actin filament' as the muscle is contracted. After ATP hydrolysis, myosin filaments return to its high-energy configuration.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

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