High affinity receptor for activated thrombin coupled to G proteins that stimulate phosphoinositide hydrolysis. May play a role in platelets activation and in vascular development. Platelets and vascular endothelial cells. The cleaved signal peptide may not be degraded and may function as an intracellular angiogenesis inhibitor peptide known as parstatin. Proteolytic cleavage by thrombin generates a new N-terminus that functions as a tethered ligand (PubMed:1672265, PubMed:7744748). Also proteolytically cleaved by cathepsin CTSG (PubMed:7744748). Cleavage at 41-Arg-|-Ser-42 by CTSG results in receptor activation while cleavage at 55-Phe-|-Trp-56 results in inhibition of receptor activation (PubMed:7744748). Phosphorylated in the C-terminal tail; probably mediating desensitization prior to the uncoupling and internalization of the receptor. Belongs to the G-protein coupled receptor 1 family.