ORTHO-AMINOBENZOIC ACID AS A FLUORESCENT-PROBE FOR THE INTERACTION BETWEEN PEPTIDES AND MICELLES

Ortho-aminobenzoic acid (o-Abz) has been used as a fluorescent probe i n internally quenched fluorescent peptides for continuous protease ass ays. We investigated the fluorescent properties of the probe in order to verify if it can be used to monitor the interaction of peptides wit h micelles. Abz-aminoacyl-monomethyl amides (Abz-Xaa-NHCH3, where Xaa = Arg, Phe, Leu and Glu) were synthesized. Quantum yield, spectral pos ition, anisotropy and lifetime decay were analyzed in the presence and absence of sodium dodecyl sulfate (SDS) micelles. Significant changes in the fluorescence parameters were observed for Abz-Arg-NHCH3 in com parison to Abz-Glu-NHCH3, indicating a strong electrostatic component in the compound's interaction with the negative charged micelles. The change in fluorescence parameters, observed when the probe is bound to hydrophobic amino acids Abz-Phe-NHCH3 and Abz-Leu-NHCH3, is probably due to insertion of those compounds into micelles. Abz-NHCH3 fluoresce nce is less affected by the presence of micelles, indicating that the occurrence of interaction is dependent on the properties of the amino acid to which the fluorophore is attached. The quenching data with acr ylamide confirmed these results. Titration curves allowed the estimati on of association constants between Abz compounds and SDS, according t o a single partition model. Although the results cannot be strictly ap plied to the titration with charged compounds, it was verified that th e association constant for the isolated Abz-NHCH3 is significantly low er than those for Abz-Phe-NHCH3 and Abz-Leu-NHCH3. It is concluded tha t the Abz group is a sensitive and convenient fluorescent probe to mon itor peptide binding to amphiphilic aggregates. That conclusion is sup ported by measurements with the peptide Abz-Leu-Arg-Phe-NH2. (C) 1998 Elsevier Science B.V. All rights reserved.