The effect of glucosyl-β-cyclodextrin on the hydrogen–deuterium exchange rate constant of the peptide bonds of chicken egg white lysozyme in a D 2O solution

Abstract

FT-IR spectroscopy revealed that the hydrogen–deuterium (H–D) exchange reaction rate of the peptide hydrogen atoms of chicken egg white lysozyme in a deuterated aqueous solution was significantly accelerated in the presence of glucosyl-β-cyclodextrin at 55 °C. The addition of methyl α- d-glucopyranoside, which has no inclusion ability, rather decelerated the H–D exchange reaction rate at the same temperature. The H–D exchange rate constant of lysozyme was evaluated by the time dependence of the absorbance ratio of the amide II infrared band against the amide I’. The H–D exchange rate constant was not influenced by the addition of glucosyl-β-cyclodextrin at 45 °C, however, it became twice larger than that in the absence of the cyclodextrin at 55 °C. These results strongly suggest that peptide bonds of lysozyme become exposed to the aqueous medium due to the inclusion by glucosyl-β-cyclodextrin to accelerate the H–D exchange rate.