Conformational change of human prothrombin induced by calcium ions: an X-ray scattering study

The scattered X-ray intensities from dilute solutions of prothrombin and Ca2+-prothrombin at 21 degrees C in 0.1 M Tris-HCl buffer of pH 7.4 indicate that the prothrombin molecule attains a more extended conformation when Ca2+ ions are bound. This is indicated from the distance distribution function: the largest distance within the prothrombin molecule increases from 130 to 150 A when Ca2+ ions are bound; the radius of gyration increases from 35.5 to 39.5 A. A comparison of the experimental scattering curves with theoretical scattering curves calculated for various triaxial bodies shows that the shape of the prothrombin molecule can be represented by two ellipsoids and that the effect of Ca2+ binding can be represented by a change in the angle between their major axes.