beta-Cyclodextrin inhibits the sweet taste suppressing activity of gurmarin by the formation of an inclusion complex with aromatic residues in gurmarin

Our recent study in mice revealed that the inhibitory activity of gurmarin on the sweet taste responses was reduced significantly by the presence of b eta -cyclodextrin (beta -CD). To investigate the mechanism involved in the action of beta -CD, physicochemical experiments were performed on the inter action of CDs with gurmarin examining the effect of CDs on the UV absorptio n spectrum of gurmarin and on the elution behavior in gel filtration (or ex clusion) chromatography. Among the three kinds of cyclodextrins tested, bet a -CD induced significant changes in the UV absorption spectrum of gurmarin that were characteristic of those found in the inclusion complex formation of tyrosine and tryptophan with beta -CD. The abnormal retention behavior of gurmarin in gel filtration resulting from hydrophobic interaction with t he gel matrix reverted to normal in the presence of beta -CD in the elution buffer. These results suggest that the unique domain of gurmarin, in which five aromatic amino acid residues are all directed outwardly and form a hy drophobic cluster, is a possible site of interaction with the gurmarin-sens itive sweet taste receptor molecules in rodents.