The action of prothrombin activated by Ecarin on fibrinogen.

Highly purified human prothrombin was activated by Ecarin, a prothrombin activating principle of Echis carinatus venom and the generated thrombin-like activity was investigated. Kinetics of the release of fibrino-peptides A and B (FPA, FPB) from human fibrinogen was estimated using radioimmunoassay technique. The direct proteolytic action of Ecarin on fibrinogen was studied by means of polyacrylamide gel electrophoresis and by radioimmunoassay for fragment B beta 15-42 of fibrinogen. In a system containing Ecarin, fibrinogen and prothrombin both fibrinopeptides were cleaved off at a rate that was essentially similar to that observed with thrombin, the cleavage off of FPB being in the initial stage always slower than the release of FPA. At physiological concentration of prothrombin and at low concentration of Ecarin all FPB were liberated while less than 1% of B beta 15-42 immunoreactivity was released. It was possible to accelerate the release of FPB when prothrombin was activated by Ecarin in the presence of Fibrin I gel (formed from fibrinogen by Batroxobin which liberates FPA only) instead of fibrinogen. Fibrin I thus constituted a more favourable substrate than fibrinogen with regard to release of FPB. The results indicate that the coagulant activity generated from prothrombin by Ecarin is thrombin-like. No intermediate product capable of marked cleavage off of FPA only was detected.