The effect of mechanical stretching of the myosin rod component (fragment [formula omitted] S-2) on the ATPase activity of myosin

Abstract

The binding myosin to nylon fiber gives immobilized myosin with a considerable ATPase activity. Treatment of immobilized enzyme with papain results in the entire ATPase activity (known to be concentrated in myosin heads (fragment HMM S-1)) being replaced from the fiber into the solution; this means that myosin is chemically bound to the fiber via its rod part (fragment LMM + HMM S-2). When nylon fiber is mechanically stretched, the ATPase activity of myosin attached to it sharply decreases; after relaxation of the fiber the enzymatic activity returns to the initial level. The detailed study of this phenomenon has shown that reversible inactivation of myosin upon fiber stretching is not the result of an altered microenvironment of the enzyme. The discovered regulatory effect is ascribed to deformation of myosin molecules induced by support stretching. Thus deformation of the myosin tail (not indispensable for ATPase since its cleaving-off does not alter the enzymatic activity) leads to decrease in the ATPase activity of the enzyme. The possible role of the above phenomenon in the mechanism of muscle contraction is discussed.