Reversibility of acid denaturation of recombinant interferon-gamma.

It has been shown that interferon-gamma (IFN-gamma) loses activity after acid treatment and this property can be used to distinguish it from other types of interferons. Therefore, reversibility of acid denaturation of IFN-gamma was examined using the recombinant human protein. The fluorescence spectra showed that conformation of the protein is similar before and after acid treatment, suggesting reversibility of the acid denaturation. The antiviral activity of the protein was also identical in the same treatment. However, the antiviral activity was significantly reduced when it was determined by directly diluting the acidic samples into the assay medium containing high salts and serum proteins. Similar results were obtained with the recombinant murine IFN-gamma. This observation demonstrates that acid denaturation of the IFN-gamma is dependent on the way the protein is renatured, and hence that the difference in response to acid treatment between IFN-gamma and other interferons is quantitative rather than qualitative.