Polymerization Sites in the D-Domain of Human Fibrin(ogen)

The present work deals with localization of previously unknown polymerization sites of the fibrin DD-fragment. D-dimer we obtained has a pronounced inhibitory effect on fibrin polymerization (IC₅₀ = 0.06 M). The inhibitory effect of the D-fragment disappeared after reduction and carboxymethylation. However, polypeptide chains _DD (B134-461) and _DD (63-411)₂ of the DD-fragment, isolated by preparative electrophoresis, displayed their inhibitory activity. For instance, the rates of fibrin protofibril lateral association were decreased twice in the presence of _DD and _DD chains at their molar ratios to fibrin of 0.40 and 0.15, respectively. The IC₅₀ values for _DD and _DD were 0.24 and 0.10 M, respectively. Highly specific inhibition of protofibril lateral association suggests that the protofibril lateral association sites are located in B134-461 and 63-411 regions of the fibrin D-domain. Our data confirm those reported by Doolittle et al. regarding the -chain and a hypothesis about -chain of fibrin D-domain (Yang, Z., Mochalkin, I., and Doolittle, R. F. (2000) Biochemistry, 97, 14156-14161).