Kinetics of actin-myosin binding. I. An exactly soluble one-variable model.

To treat the kinetics of actin-myosin binding as simply as possible, a one-variable model is developed and the notion of effectivity factors is introduced. An effectivity factor is a ratio of the reaction rate in the presence of cooperativity to that in the noncooperative case and is calculated by averaging cooperativity factors over all sites belonging to one seven-site actin unit. The technique is applicable to a variety of models involving cooperative association and dissociation processes. This averaging assumes the equivalence of all regulated actin units. The model may be solved exactly for arbitrary degrees of "preloading" of subfragment 1 (S1) on the regulated actin.