Boophilus microplus anticoagulant protein: An antithrombin inhibitor isolated from the cattle tick saliva

An anticoagulant was isolated from saliva of the cattle tick Boophilus micr oplus. Crude saliva prolonged both recalcification time and prothrombin tim e in assays with bovine plasma. It also inhibited thrombin, but not Ma, ami dolytic activity. We purified the antithrombin activity by a combination of gel filtration, anion exchange, and affinity chromatography. The purified inhibitor has a molecular weight of 60,000 Da, determined by SDS-PAGE. The anticoagulant IC50 varied from 100 nM to 1.1 muM, depending on the thrombin concentration and substrate used (fibrinogen or platelet receptor). The ex cess of inhibitor in relation to thrombin indicates that it is not a tight- binding inhibitor. Chromogenic assays using a panel of five serine-proteina ses suggest that the inhibitor is specific against thrombin. (C) 2000 Acade mic Press.