Mechanism of Ancrod Anticoagulation A DIRECT PROTEOLYTIC EFFECT ON FIBRIN

tilase, or thrombin was reduced by P-mercaptoethanol and examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It was found that ancrod progressively and totally digested the a-chains of fibrin monomers at sites different than plasmin; however, further digestion of fibrin monomers by either reptilase or thrombin was not observed. Highly purified ancrod did not activate fibrin-stabilizing factor (FSF); however, the reptilase preparation used in these experiments, like thrombin, ac-tivated FSF and thereby promoted cross-link formation. Fibrin, formed by clotting purified human fibrinogen with ancrod, reptilase, or thrombin for increasing periods of time in the presence of plasminogen, was incubated with urokinase and observed for complete lysis. Fibrin formed by ancrod was strikingly more vulnerable to plasmin di-gestion than was fibrin formed by reptilase or thrombin. The lysis times for fibrin formed for 2 hr by ancrod, rep-tilase, or thrombin were 18, 89, and 120 min, respectively. Evidence was also obtained that neither ancrod nor rep-tilase activated human plasminogen. These results indi-cate that fibrin formed by ancrod is not cross-linked and has significantly degraded a-chains; as expected, ancrod-formed fibrin is markedly susceptible to digestion by plasmin