Striking susceptibility of a kinin-yielding pentadeca-peptide to tryptic hydrolysis

Hydrolysis of Lys-Arg-Pro-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Val-Gln-Val-Ser by trypsin (EC 3.4.21.4) yields lysyl-bradykinin by rupture of the Arg-Ser bond. The k_cat/K_m value found for this hydrolysis was 1.4 × 10¹⁰ M^?1 × sec^?1, which is 10^?5-fold higher than that obtained for the hydrolysis of bradykinyl-Ser-Val-Gln-Val-Ser. This effect was abolished by acetylation of the lysine amino groups of the pentadecapeptide. Contrarywise, the esterolytic activity of trypsin on bradykinin methyl ester was the same as in lysyl-bradykinin methyl ester. The high susceptibility of Lys-bradykinyl-Ser-Val-Gln-Val-Ser to trypsin catalysis is striking because: a) it constitutes the first example that an amino acid residue distant from the bond split may enhance trypsin catalysis; b) this pentadecapeptide is the best synthetic substrate so far described for trypsin and c) the value of k_cat/K_m for its hydrolysis is unusually high for proteases.