Abstract
Altering the aqueous environment, especially with agents that affect hydrogen bonds, markedly affects the stability of mouse L cell interferon. Low pH stabilizes interferon whereas high pH labilizes it; heavy water further enhances interferon thermostability at pH 2 but not at pH 9. Exposure to the protein denaturants, 4 M-guanidine hydrochloride and 6 M-urea, significantly decreases the activity of interferon at pH 2 and pH 9; however, the residual interferon activity is relatively thermostable. Certain chaotropic salts protect interferon against thermal destruction, and in terms of effectiveness, their sequence is in the order SCN- > I- Cl- = ClO4- = Br- > NO3-. Interferon becomes more stable to heat as the NaSCN concentration is increased from 0.25 M to 2.0 M. Molecular sieve chromatography of interferon in the presence of 1.5 M-NaSCN at pH 7 shows a shift in its apparent mol. wt. from 25000 to 42000. Unlike most proteins, the unfolded conformation of interferon appears to be more stable to heat than the molecule with a smaller Stokes' radius.