Segmental flexibility in the myosin molecule: evidence from binding studies of myosin fragments with actin.

From comparative studies of the association with polymeric actin of the bifunctional species heavy meromyosin and its monofunctional constituents, information about the relative freedom of these paired elements can be derived. An isotherm for the former binding process is presented which involves, as an experimentally determinable parameter, the local concentration of second segment after the first of a pair is attached to the lattice. From combined data for these two association reactions a value of 10(-4) M is obtained for this quantity. The large degree of segmental flexibility reported for the free heavy meromyosin is still manifested in the association with actin.