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

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Abstract
The scattered X-ray intensities from dilute solutions of prothrombin and Ca2+-prothrombin at 21.degree. 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 .ANG. when Ca2+ ions are bound; the radius of gyration increases from 35.5 to 39.5 .ANG.. A comparison of the experimental scattering curves with theoretical scattering curves calculated from various triaxial bodies shows that the shape of the prothrombin molecule can be represented by 2 ellipsoids and that the effect of Ca2+ binding can be represented by a change in the angle between their major axes.