Effect of Substrate on the Conformation of Myosin

In order to resolve conflicting reports in the literature, the optical rotatory dispersion and far ultraviolet absorption spectrum of myosin, and in particular heavy meromyosin, have been examined in the presence and absence of ATP and the specific inhibitor, pyrophosphate. By neither criterion is there a measurable change and it is concluded that any change in the α-helix content is less than 0.2%; i.e. it involves fewer than about 6 residues per molecule of myosin. Changes in the binding capacity for bromothymol blue are observed when ATP or pyrophosphate is added to myosin or heavy meromyosin, which supports the view that a small conformational change occurs. The absence of any gross deformation of the myosin molecule by substrate or inhibitor has been established by a difference sedimentation method. Some implications of the findings in relation to current concepts of myosin function are considered.