The peptide YFLLRNP is an antagonist to thrombin and SFLLRNP (thrombin receptor agonist peptide) in human platelets. YFLLRNP can induce partial activation of human platelets, visible by shape change; but it is unable to fully activate the platelets.
Rasmussen, UB. et al. J Biol Chem 268, 14322 (1993).