Synthesis and use of an aminoquinolinone derivative for the fluorometric determination of oxytocinase

Abstract

A new fluorogenic substrate for the determination of the activity of human serum oxytocinase-cystine aminopeptidase (EC 3.4.11.3), H-Cys(Bzl)-NH-Meq, has been synthesized. The affinity of H-Cys(Bzl)-NH-Meq to oxytocinase was by two orders higher than that of the usually employed chromogenic substrates. The Michaelis constant of oxytocinase for this substrate was within the range of the optimum pH (7.0–7.5) 2.3.10-6 mol l-1, i.e. in the region of the affinity of the natural substrate, oxytocin. The concentration of dimethylsulfoxide used for the solubilization of H-Cys(Byl)-NH-Meq (<0.4%) did not influence adversely the course of the enzyme reaction as in the case of chromogenic substrates, where the concentrations of the organic solvent exceeded 3%.