An Inhibitor of Activated Factor XIII, Inhibiting Fibrin Cross-Linking but not Incorporation of Amine into Casein

Abstract

The inhibitor was quantitatively separated together with the Ig[immunoglobulin]G fraction of plasma [human], but attempts to neutralize the purified inhibitor by commercial anti-IgG sera gave inconstant results, possibly due to anti-factor XIII activity demonstrable in these sera. The inhibitor prevented crosslinking by activated factor XIII, even when tested on preformed fibrin, but was inactive when assayed by the use of a synthetic substrate (monodansylcadaverine). Since the inhibitor remained in the supernatant after defibrination, and was not associated with the clottable proteins, the present findings suggest inhibition of activated F XIII and not blockade of cross-linking sites on fibrinogen.