The Sequence γ-(312-324) Is a Fibrin-Specific Epitope

Fibrin accelerates the activation of plasminogen catalyzed by tissue-type plasminogen activator much stronger than fibrinogen. Detailed studies showed that (part of) this rate-enhacing effect of fibrin is brought about by two sites in the fibrin molecule: one in Aα-(148-160) and one in the γ-chain stretch 311-379 (also known as FCB-5). During the fibrinogen-to-fibrin conversion, Aα-(148-160) appears to become accessible, because a monoclonal antibody against synthetic Aα-(148-160) reacts with fibrin, but not with fibrinogen. Because a similar situation may exist for (at least parts of) FCB-5, we have prepared a monoclonal antibody against a part (ie, γ-[312-324]) of FCB-5, and found that this is fibrin-specific and does not bind fibrinogen. We conclude that γ-(312-324) is hidden in fibrinogen and is exposed by the formation of fibrin.