Synthetic substrates for human factor VIIa and factor VIIa-tissue factor

A series of 100 tripeptide fluorogenic substrates has been synthesized. These substrates contain Arg in the P1 position, various amino acids in the P2 and P3 positions, and different 6-amino-1-naphthalenesulfonamides (ANSN) as the detecting group (P'). The 38 compounds possessing the highest initial rates of factor VIIa hydrolysis were evaluated for substrate kinetic parameters in the presence and absence of tissue factor (TF) and by factor Xa. Most of these substrates had a higher kcat/KM (keff) value for the factor VIIa-TF complex than for factor Xa. Substitution of different amino acids in the P2 position showed that substrates with bulkier amino acids such as Leu, Pro, and Val have higher values for KM and kcat than those with smaller amino acids (Gly or Ser). The highest second-order rate constants were found for substrates with Val or Pro in the P2 position. A decrease or increase in volume of the P2 substituent (Gly, Ser, or Leu) resulted in a decrease in this constant. Substrates with the highest keff values have Phe in the P3 position. As the hydrophobicity and volume of the amino acid in the P3 position decreased, the keff was reduced. The efficiency of substrates for hydrolysis by factor VIIa was enhanced by an increase of hydrophobicity in the P' structure. TF enhanced the amidolytic activity of the "family" of 38 substrates with ANSN in the P' position on an average of 58-fold.