Schematic representation of the extracellular aminoterminal domain of the thrombin receptor with the potential cleavage sites generated by HLE, Cat G, and PR3. The sequence of the thrombin receptor located between Asn35 and Pro⁸⁵ is represented using the single-letter code for amino acids.15 Synthetic peptides used in this study and mapping over this domain are located by thin lines. Bold lines represent the putative sequences Gln⁸³-Ser⁹³ and Ile²⁴⁴-Ala²⁶⁸ involved in the binding of the tethered ligand.19-21 Large arrowheads indicate cleavage sites observed as soon as 1 minute of proteolysis in MALDI-TOF mass spectrometry studies, whereas the small arrowhead shows a cleavage detected after 30 minutes (Cat G, ; HLE, ▴; PR3, ). The white arrowhead (▵) indicates the cleavage site determined for thrombin.15