The Effects of Cyclodextrins on the Thermal Denaturation and Renaturation Processes of Bovine Pancreatic Ribonuclease A in an Aqueous Solution Studied by Circular Dichroism and Fluorescence Spectroscopy.

Circular dichroism and fluorescence spectroscopic measurements showed that the thermal denaturation and renaturation processes of bovine pancreatic ribonuclease A (RNase A) in an aqueous solution at pH 7.0 are greatly affected by the addition of glucosyl-β-cyclodextrin (G1-β-CD). The result of circular dichroism measurements revealed that G1-β-CD lowered the thermal stability of RNase A to result in an irreversible denaturation of RNase A in the aqueous solution. The α- and γ-cyclodextrin gave less effect on the thermal stability. The ellipticity at 220 nm of the thermally denatured RNase A scarcely recovered with the re-cooling process in the presence of G1-β-CD. The temperature dependency of the fluorescence intensity at 309 nm due to six tyrosine residues of RNase A was significantly affected by the addition of G1-β-CD. The effect of the addition of CDs on the thermal stability was larger in the order of G1-β-CD > γ-CD > α-CD.