Structure of the prothrombin- and blood clotting factor X-membrane complexes

The configuration of the prothrombin- and factor X-membrane complexes was investigated by the technique of quasielastic light scattering. It is concluded that the fragment 1 region of prothrombin is located at one end of the prothrombin molecule and that the membrane binding site is at the tip of the fragment 1 region. Prothrombin binds to the surface of the membrane with no detected penetration into the lipophilic region of the membrane. The remainder of the prothrombin molecule extends radially from the membrane surface with maximum protrusion into solution. Factor X also binds to the membrane at one end of the molecule and extends into solution. Based on the evidence presented here and in other communications [Nelsestuen, G. L., and Lim, T. K. (1977), Biochemistry 16, and Nelsestuen, G. L., and Broderius, M. (1977), Biochemistry 16 (respectively the first and second in a series of three papers in this issue)] a model for prothrombin-membrane interaction is given. Quasielastic light scattering appears to be a valuable new method for studying protein-membrane interactions.