Dynamic viscoelastic study of the effect of beta-actinin on the interaction between F-actin and heavy meromyosin.

Beta-Actinin, a regulatory protein of muscle, greatly decreased the dynamic rigidity modulus of an acto-heavy meromyosin solution. However, it was found that the mechanical mixing procedure used resulted in fragmentation of the decorated F-actin particles and beta-actinin inhibited the reassociation of the fragmented particles. This was the reason for the decrease of the dynamic rigidity modulus of the acto-heavy meromyosin complex caused by beta-actinin. When beta-actinin was added to the acto-heavy meromyosin solution in the presence of ATP, it did not affect the visco-elasticity. F-actin particles dissociated by ATP were not fragmented by the mixing procedure, which was responsible for the apparent inactivation of beta-actinin in the presence of ATP.