Oxygen Exchange Reaction during ATP Hydrolysis by Glycerinated Muscle Fibers, Myofibrils, and Synthetic Actomyosin Filaments

Abstract

The oxygen exchange during ATP hydrolysis by glycerinated muscle fibers, myofibrils, and synthetic actomyosin filaments was studied from the distribution of the [¹⁸O]P₁, species produced by the hydrolysis of [γ-¹⁸O]ATP. The products were mixtures of two species, one with a low extent of oxygen exchange and the other with a high extent. The low and high extents of oxygen exchange in these two P¹, species were the same as those of the acto-S-1 ATPase reaction through the routes with and without the dissociation of actomyosin, respectively (Yasui, M., Ohe, M., Kajita, A., Arata, T., & Inoue, A. [1988] J. Biochem. 104, 550-559). During isometric contraction of glycerinated muscle fibers at 20°C, the fraction of ATP hydrolysis with low extent of oxygen exchange was 0.83 and 0.70, respectively, in 0 and 120 mM KC1. In myofibrils, the fraction of ATP hydrolysis with a low extent of oxygen exchange was 0.72-0.88 in 0-120 mM KC1 at 20°C. Therefore, in glycerinated muscle fibers and myofibrils ATP seems to be mainly hydrolyzed through a route without the dissocia-tion of actomyosin, especially at low ionic strength and at room temperature when the tension development is high. ATP hydrolysis through this route may be coupled with muscle contraction.