Significance of tryptophan residues in the D-domain of the fibrin molecule in fibrin polymer formation.

The modification of fibrin monomer with H2O2 caused reduction of the association activity of fibrin monomer. The association activity was not reduced even by modification of approx. 16 out of the total 64 tryptophan residues in the fibrin molecule; it was then abolished by further modification of the following several residues. Fragment D obtained by proteolysis of fibrinogen with plasmin, inhibited the association activity of fibrin monomer and the modification of approx. six out of the total 21 tryptophan residues in the fragment led to the complete loss of the inhibitory effect. It was concluded from these studies that about six tryptophan residues in the D-domain of fibrin are important for the association of fibrin monomer.