[Equilibrium system consisting of soluble forms of fibrin and the specific anticoagulant D fragment of the firbinogen molecule].

According to the authors' observations, mixtures of fibrin monomer and fibrinogen-derived D fragment are gradually transformed into an equilibrium system when fibrin exists partly in a solid clot form and partly as a soluble material made unclottable by the influence of fragment D. The amount of such a soluble fibrin proved to be a linear function of the D fragment concentration. Three fibrin monomer preparations obtained in different ways were used. All of them showed similar properties as to the modifications with D fragment. The solubilzing activity of D fragment in the equilibrium system could sharply be raised by increasing ionic strength or pH. It is known that these medium changes produce the same stimulation effect on D fragment, being examined as an inhibitor of fibrin monomer polymerization. But the concentration dependences of the two activities of D fragment differ in principle.