plate lets to collagen nor the ca 2 dependent adhesion of platelets to fibrinogen is affected by this peptide furthermore fn 312 326 also appears to be specific in its ability to inhibit the divalent cation independent component of platelet adhesion to fn inhibiting only about half of the total platelet adhesion in the presence of ca 2 neither the peptide fn 312 333 which lacks the initial four amino acids tavt seq id no 13 in the 15 amino acid peptide fn 312 326 nor the peptide tavtqty seq id no 2 which represents the first seven amino acids of fn 312 326 inhibit platelet adhesion to the 45 kda gelatin binding domain of fn thus while the sequence tavtqty seq id no 2 is important for recognition of the peptide it appears that at least some of the succeeding five amino acids ggnsngep seq id no 10 are required for peptide binding to the receptor removal of the carboxy terminal three amino acids gep from fn 312 326 on the other hand reduces the apparent affinity of the peptide by approximately 10 fold compared to the parent peptide but does not abolish its ability to inhibit divalent cation independent platelet adhesion to 45 kda thus the entire sequence of fn 312 326 appears to be necessary for the maximum inhibition of this adhesive.