Mechanochemical model for myosin II dimer that can explain the spontaneous oscillatory contraction of muscle

The spontaneous oscillatory contraction (SPOC) of myofibrils is the essential property inherent to the contractile system of muscle. Muscle contraction results from cyclic interactions between actin filament and myosin Ⅱ which is a dimeric motor protein with two heads. Taking the two heads of myosin Ⅱ as an indivisible element and considering the effects of cooperative behavior between the two heads on rate constants in the mechanochemical cycle, the present work proposes the tenstate mechanochemical cycle model for myosin Ⅱ dimer. The simulations of this model show that the proportion of myosin Ⅱ in different states periodically changes with time, which results in the sustained oscillations of contractive tension, and serves as the primary factor for SPOC. The good fit of this model to experimental results suggests that the cooperative interaction between the two heads of myosin Ⅱ dimer may be one of the underlying mechanisms for muscle contraction.