Fluorescence spectroscopic determination of the critical aggregation concentration of the GnRH antagonists Cetrorelix, Teverelix and Ozarelix.

The fluorescence spectroscopic behavior of three 2-naphthylalanine containing Gonadotropin-releasing hormone (GnRH) antagonists Cetrorelix, Teverelix and Ozarelix has been investigated concerning their aggregation process in comparison to the non-aggregating peptide D-Phe(6)-GnRH. The aim of the present investigation consisted in developing a method to determine the critical aggregation concentration for these decapeptides. This was achieved by monitoring the incorporation of the fluorescent probe 1-anilino-8-naphthalene sulfonate (ANS) into aggregates and utilizing the modification of band shape and intensity of the intrinsic peptide fluorescence emission depending on the analyzed peptide concentrations. Finally an approach for the explanation of the observed band characteristics is presented analyzing the fluorescence of fragments Cetrorelix(1-4) and Cetrorelix(1-6).