Inhibition of bradykinin-induced contraction of isolated smooth muscle tissue preparations by oligopeptide thiobenzyl ester substrates for serine proteases.

Synthetic peptide substrates containing various chromophores and fluorophores have been utilized in the quantitation of serine protease activities. Recently, amino acid thiobenzyl esters containing arginine and lysine have also been used to evaluate the serine proteases. In an attempt to develop specific peptide thiobenzyl substrates, we have screened D-Pro-Phe-Arg-S-CH2-C6H5, D-Phe-Phe-Arg-S-CH2-C6H5, D-Gly-Pro-Arg-S-CH2-C6H5, and D-Val-Leu-Lys-S-CH2-C6H5 to determine the enzymatic activity of serine proteases. Since we found that D-Pro-Phe-Arg-pNA is a potent inhibitor of the bradykinin induced contractile action of isolated smooth muscle preparations such as the guinea pig ileum and rat uterus, we screened D-Pro-Phe-Arg-S-CH2-C6H5 at a 5 X 10(-5) M and found that it completely blocked the bradykinin (1 ng) induced contraction of the isolated rat uterus preparation. Other peptide thiobenzyl esters produced somewhat weaker effects, however, none of the free peptides not C6H5CH2SH, at concentrations of up to 10 microns, produced any significant contraction or inhibition of the isolated smooth muscle preparation. These observations suggest that peptide thiobenzyl esters are effective blockers of bradykinin induced contraction of the isolated smooth muscle preparations and the amino acid sequence of the peptides plays an important role in the determination of relative potency of each of these peptide derivatives. Moreover, the result of this investigation provides the basis for a new approach to further design specific inhibitors of the pharmacologic actions of biologically active peptides.