SURFACE-INDUCED DENATURATION OF PROTEINS DURING FREEZING AND ITS INHIBITION BY SURFACTANTS

In this study, we found that the denaturation of proteins during freez ing is closely related to surface-induced denaturation. Several protei ns with varying sensitivities to freezing were tested, and the results were compared with susceptibilities to surface denaturation in unfroz en aqueous solution. Also, the influence of the surfactant Tween 80 on the denaturation of each of the proteins was examined during freeze-t hawing, as were the effects of Tween 80 and several other surfactants on the stability of lactate dehydrogenase. Proteins formed insoluble p recipitates when they were subjected to a quench cooling by dipping in liquid nitrogen, although freezing followed by supercooling caused le ss precipitation. A strong correlation (r = 0.99) was observed between the tendency of a protein to freeze denature and its tendency to surf ace denature. Also, the addition of small amounts of surface-active ag ents protected proteins from both freeze- and surface-induced denatura tion. Freeze-induced denaturation of IL-1ra at the ice-water interface during freeze-drying was effectively prevented by adding a small amou nt of Tween 80. These results suggest that the denaturation of protein s during freeze-thawing can be ascribed primarily to the increase in t he area of the ice-water interface during freezing.