Circular Dichroism and Fluorescence Spectroscopy Studies of the ffect of Cyclodextrins on the Thermal Stability of Chicken Egg White Lysozyme in Aqueous Solution

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Circular dichroism spectroscopy revealed that the thermal stability of chicken egg white lysozyme in an aqueous buffer solution is significantly lowered by the addition of 6-O-α-D-glucosyl-β-cyclodextrin (G1-β-CD), whereas it is raised by the addition of methyl α-D-glucopyranoside. The α- and γ-cyclodextrin also lowered the thermal stability, although the effects were less prominent than that of G1-β-CD. Fluorescence spectroscopy suggested that cyclodextrins include the side chains of tryptophan residues within their internal cavities to lower the thermal stability of lysozyme. The fluorescence intensity of a sample, re-cooled to 25℃ after thermal denaturation at 75℃ in the presence of G1-β-CD, was stronger than that observed for native lysozyme. The fact that the fluorescence intensity of the re-cooling sample was stronger than that of the native one indicates that G1-β-CD persists in binding to the side chains of tryptophan residues of the re-cooled lysozyme.