Prothrombin domains: circular dichroic evidence for a lack of cooperativity

Abstract

The far-UV circular dichroism spectra of bovine and human prothrombin, prothrombin fragment 1, prethrombin 1, prothrombin fragment 2 and prethrombin 2 (prethrombin 2des(1-13)) were determined. The method of Chen et al. was used to calculate the apparent .alpha.-helix, .beta.-sheet and random-coil contents of each protein. Prothrombin and its activation components contained a large amount of aperiodic secondary structure and there was little species difference between the spectra and, thus, secondary structures. The hypothesis that the prothrombin activation components exist as relatively noncooperative domains within the prothrombin molecule was tested by comparing the circular dichroism spectrum of prothrombin with the sum of the spectra of the components. In support of the hypothesis, no gross occurred upon activation.