THE BINDING OF FREE OLIGOPEPTIDES TO CYCLODEXTRINS - THE ROLE OF THE TYROSINE GROUP

The formation of alpha-cyclodextrin (alpha-CD) and beta-cyclodextrin ( beta-CD) inclusion complexes with free tyrosine and the tyrosine resid ues within two free oligopeptides were investigated using steady-state fluorescence spectroscopy. The oligopeptides consist of five amino ac ids (pentapeptide) and the tyrosine residues are located at the n-term ini. The two peptides used in this study have well-known biological fu nctions and are known to bind selectively to specific cell receptors. Cyclodextrins were used to model this receptor-peptide (protein-ligand ) interaction. Equilibrium binding constants and the enthalpy and entr opy of binding were recovered. Molecular size of the tyrosine-containi ng species and pH (7.0 vs. 10.0) were found to have little affect on a lpha-CD binding. However, tyrosine binding to beta-CD was dependent on the size (free tyrosine vs. peptide), structure, and pentapeptide con formation.