Dissociation of the subunit structure of fibrin stabilizing factor during activation of the zymogen

Summary Calcium ions play an essential role in the zymogenic conversion of the fibrin stabilizing factor (FSF; Factor XIII of plasma) in that they cause a dissociation of the two types of subunits ( a′ from b ) of the thrombin-activated factor (FSF′). Disc gel electrophoresis carried out under non-denaturating conditions and utilizing a newly developed fluorescent activity staining procedure is eminently suited for demonstrating changes in the quaternary structure of this protein. Also, kinetic evidence is presented to show that the b type of subunit, though enzymatically inactive, plays a role in regulating the rate of the calcium dependent activation of the zymogen.