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 addition of G1-β-CD lowered the thermal stability of RNase A to occur an irreversible denaturation of RNase A in the aqueous solution. The α- and γ-cyclodextrin gave less effect on the lowering of thermal stability. The ellipticity at 220 nm of the thermally denatured RNase A scarcely recovered with the re-cooling process with the addition of G1-β-CD. The temperature dependency of the fluorescence intensity at 309 nm arising from six tyrosine residues of RNase A was significantly affected by the addition of G1-β-CD. The effect of the addition of CDs was larger in the order of G1-β-CD > γ-CD > α-CD.