We report the structural requirements of the C-terminal tripeptide derivative of Fas (Ac-Ser- Leu-Val-OH, 1) for the inhibitory activity of Fas/FAP-1 binding. The presence of a carboxyl group and a l-Val residue at the C-terminus is essential for the inhibitory activity, and the hydroxyl group of Ser plays an important role as the donor of a hydrogen bond. The introduction of hydrophobic groups to the N-terminal region of 1, especially the ...