Myosin relaxation phase

In the relaxation phase of muscle contraction, the S-1 head of myosin hydrolyzes ATP to ADP and Pj, but these products remain bound. The resultant ADP-Pj-myosin complex has been energized and is in a so-called high-energy conformation. 

Somewhat similar considerations were also applied to acto-myosin systems, for which enhanced fluidization was predicted due to actin-driven sliding of filaments.For actin networks, it has long been known that the addition of myosin motors can cause network contraction and eventually a macroscopic phase separation, a process dubbed super-precipitation. Under certain conditions, however, enhanced fluidization due to an increased rate of stress relaxation was foimd in solutions of non-CTOss-linked actin that was activated by minifilaments of skeletal muscle myosin II. The gels were foimd to soften at low frequencies. This can be explained by an increase in the rate of stress relaxation in the entangled networks when motors actively slide the filaments arormd the obstacles. This sliding can also lead to the formation of bundled or oriented/polar-ized states of actomyosin gels. There bave been a number of hydrodynamic-like theories developed for such fluidlike active gels. "... 

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