Temperature-induced structural changes in chicken egg white ovomucoid.

Abstract

Temperature-induced structural changes in chicken egg white ovomucoid were investigated by circular dichroism (CD) and ultraviolet absorption (UV). A major unfolding transition was brought about between 60 and 90°C with a rise in temperature, as monitored by variations in CD at 222 nm and UV at 287 nm. Thermal transition was reversible when there was no prolonged exposure to the denaturing condition. The Van't Hoff plot for the major unfolding process of the ovomucoid yielded the following thermodynamic parameters at pH 7.0 between 60 and 90°C: δHVH=73 kcal.mol-1 at 74°C and δSVH=209 cal.deg-1. mol-1 at 74°C, on the assumption of a two-state transition. The equilibrium CD spectra at various temperatures suggested that the secondary structure change caused by heating from 20 to 60°C was qualitatively different from that from 60 to 90°C. By prolonged exposure to high temperature of 90°C, the reversible denatured state was slowly transformed into an irreversible denatured state.