[Effect of phosphorylation of myosin light chains on the interaction of myosin minifilaments with F-actin].

The effect of phosphorylation of light chains-2 (LC2) of rabbit skeletal muscle myosin on the interaction of myosin minifilaments with F-actin as well as on the actin-stimulated Mg2+-ATPase of minifilaments was studied. It was shown that in the absence of KCl the degree of F-actin-induced stimulation of myosin minifilament Mg2+-ATPase with phosphorylated LC2 exceeds 2-4-fold that with unphosphorylated LC2. Phosphorylation of LC2 considerably increases the rate of actin-stimulated Mg2+-ATPase reaction of myosin minifilaments but exerts only a very weak influence on the affinity of minifilaments for F-actin. After addition of KCl the differences in the actin-stimulated Mg2+-ATPase activity disappear in a great degree; in the presence of 50 mM KCl they do not exceed 50%. It was assumed that the observed specific influence of LC2 phosphorylation on the kinetic parameters of actin-stimulated Mg2+-ATPase reaction of myosin minifilaments is due to unique properties of the minifilaments (e.g., their ability to ordered self-assembly as a result of interaction between the heads of myosin molecules) which reflect their structural peculiarities.