Photooxidation of fibrinogen in the presence of methylene blue and its effect on polymerization.

Human fibrinogen was illuminated in the presence of methylene blue. The resulting photooxidized fibrinogen was devoid of polymerization activity and thrombin-induced coagulability. The initial rate of the thrombin catalysed release of fibrinopeptides from photooxidized fibrinogen was normal. It was shown that illumination of photooxidized fibrinogen and photooxidized fragment N-DSK caused the modification of histidine residues. Tryptophan residues were also modified. When fibrinogen was photooxidized immediately after the addition of thrombin, the capacity to polymerize was lost. The inhibition of polymerization was less marked when oxidation was initiated at the time when polymerization began or thereafter. Photooxidized fibrinogen acts as an inhibitor of the polymerization of fibrin monomers. Photooxidized fibrinogen has affinity for thrombin-activated fibrinogen-Sepharose and thrombin-activated fragment N-DSK-Sepharose. When the former conjugate is illuminated in the presence of methylene blue its affinity for fibrinogen is decreased. It is concluded that the fragment N-DSK domain of fibrinogen is affected by photooxidation.