Tick salivary thrombin inhibitor that plays an important part in the anti-hemostatic strategy of ticks. Inhibits thrombin-induced platelet aggregation, but has no effect on ADP- or collagen-induced aggregation (PubMed:10502470). Is a competitive, slow-, tight-binding inhibitor of thrombin (Ki=4.89 pM) (PubMed:10502470). It requires thrombin fibrinogen-binding exosite for optimal inhibition, as its affinity for thrombin lacking the exosite is much lower (Ki=22.3 nM) (PubMed:10502470). Its N-terminal amino acid residues may bind inside the active site cleft of thrombin, while its C-terminal domain may interact with the basic fibrinogen recognition exosite of thrombin (PubMed:12044499). It does not inhibit plasmin, factor Xa (F10), and trypsin (PubMed:10502470). Expressed in salivary glands.