[Properties of 2 fibrin monomer forms which differ in the degree of thrombin activation. Relation of these 2 forms to specific polymerization inhibitors]

The inhibitory effect of fibrinogen and its fragment D on the clotting of two fibrin monomer species has been studied. One of them (f0) lacks peptides A and B, the other (fB) preserves peptides B. The inhibitors retard the clotting of f0 but fail to influence fB polymerization. This means that the peptide B removal and appearance of the active site B in the central (E) domain of the fibrin molecule is a prerequisite for the inhibitory effect of fibrinogen or fragment D. The specificity of this effect suggests that fragment D and the periferal D-domains of fibrinogen possess a special site (B') which reacts selectively with the fibrin active site B to block polymerization. The present investigation has demonstrated the importance of the H-bond system formation for B-B' sites interaction.