Biochemical characterization of a thrombin inhibitor from the bloodsuckingbug Dipetalogaster maximus

From the bloodsucking bug Dipetalogaster maximus, a protein with anticoagul ant activity was isolated and biochemically characterized. The isolated pro tein, named dipetalogastin, possesses an average molecular mass of 11.8 kD. Its N-terminal sequence shows homology to rhodniin, a thrombin inhibitor i solated from the bug Rhodnius prolixus. The in vitro anticoagulant activity of dipetalogastin occurs via the inhibition of thrombin. The anticoagulant and thrombin inhibitory potency of dipetalogastin is comparable to that of recombinant hirudin, Its specific thrombin inhibitory activity is 9,300 an tithrombin units/mg protein. dipetalogastin forms only 1:1 molar complexes with thrombin, It is a right-binding inhibitor of thrombin possessing a dis sociation constant of 125 fM. It does not inhibit factor Xa or alpha-chymot rypsin and only weakly inhibits trypsin. Copyright (C) 2000 S. Karger AG, B asel.