Effect of Chaotropic Salts and Protein Denaturants on the Thermal Stability of Mouse Fibroblast Interferon

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Abstract
Altering the aqueous environment, especially with agents that affect hydrogen bonds, markedly affects the stability of mouse [fibroblast] L cell interferon. Low pH stabilizes interferon; 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; 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-.gtoreq. Cl- = Cl04- = 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 MW from 25,000 to 42,000. Unlike most proteins, the unfolded conformation of interferon appears to be more stable to heat than the molecule with a smaller Stokes'' radius.

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