The calcium-induced dissociation of human plasma clotting Factor XIII

Abstract

1. Large quantities of human Factor XIII were prepared from ethanol precipitates of outdated human plasma. 2. Material homogeneous after chromatography on DEAE-cellulose was further resolved into two proteins, A and B, after filtration on Sepharose 6B. 3. Protein A has a molecular weight of 350000 and a subunit structure a(2)b(2) and is activated by thrombin and calcium. Protein B is inactive and probably has a subunit structure b(2). 4. Calcium causes protein A, after thrombin cleavage, to fragment to give protein B and a protein, containing only a' subunits, which is catalytically active. The latter protein slowly forms a misty precipitate which is still active and not cross-linked covalently. This confirms the suggestion of Schwartz et al. (1971) that catalytic activity is only associated with a' subunits. 5. Iodoacetate, which inhibits the enzyme, does not inhibit dissociation and aggregation of protein A. 6. The existence of two proteins and the fragmentation are possible explanations for the wide range of molecular weights given for Factor XIII in the literature.

Primary structure of blood coagulation factor XIIIa (fibrinoligase, transglutaminase) from human placenta.

“…By measurement of the incorporation of iodo[14C]acetic acid, Chung et al (17) concluded that all of the free -SH groups of plasma FXIII are in the a chains and that each a chain has six -SH groups and no disulfide bonds. Others showed that there is a single reactive cysteine per a chain (3,12,20 (3,5,10,12).…”

“…On the basis of our studies and earlier data, we propose a molecular model for FXIIIa that shows the sites of activation and inactivation by thrombin and the location of the reactive thiol center and of a putative Ca2+-binding domain. (12), in which a TSK G4000SW column (7.5 mm i.d. x 60 cm, 8020 Biochemistry: Takahashi et al…”

Identification of the Calcium Binding Site and a Novel Ytterbium Site in Blood Coagulation Factor XIII by X-ray Crystallography

“…In the blood, activation of circulating fXIII requires thrombin cleavage, calcium ions (1.5 mM) (12)(13)(14), and fibrin(ogen) (15). High levels of calcium (Ͼ50 mM) can activate fXIII without the use of thrombin (15), and it has recently been shown that platelet fXIII can be activated nonproteolytically in vivo (16).…”

Differences between Type I Autoimmune Inhibitors of Fibrin Stabilization in Two Patients with Severe Hemorrhagic Disorder

“…As such, these inhibitors should be classified as Type I within the context of inhibitors giving rise to hemorrhagic disorders of fibrin stabilization (2). Conversion of the plasma zymogen to the active transamidase is known to occur in two distinct steps (21)(22)(23)(24). The first is catalyzed by thrombin and the second depends rather specifically upon the presence of Ca21 ions.…”

“…The first is catalyzed by thrombin and the second depends rather specifically upon the presence of Ca21 ions. Modification of the ab ensemble in the zymogen by thrombin affects only a and, while converting this subunit to a somewhat smaller a' component (25,26), it allows the two different subunits to remain associated within an a'b protomer (21)(22)(23)(24). Furthermore, the hydrolytically altered species still has no measureable transamidase activity (21,22 and while IgG Warsaw produced a complete inhibition (as long as it was applied bef'ore adding Ca2+; vertical broken line), remarkably IgG San Juan had no effect whatsoever on the platelet factor (Fig.…”