Association and dissociation properties of natural human interferon gamma

The properties of natural human interferon gamma (IFN-gamma) molecules dissolved in protein-denaturing and non-denaturing solvents were examined by high-performance size-exclusion chromatography on a gel permeation column. IFN-gamma and tritium-labeled IFN-gamma molecules formed either dimers (>90.5%) with the molecular mass of 60 kDa or probably tetramers (<9.5%) with the molecular mass of approximately 100 kDa in non-denaturing solvents, and no monomer was detected. These oligomers were dissociated in protein-denaturing solvents such as 6 M guanidine hydrochloride, and IFN-gamma existed as monomers. There is no effect on formation of the monomer based on the dissociation of oligomers by acid treatment at pH 4.0. The monomers in protein-denaturing solvents formed dimers by association when applied to a column equilibrated with a non-denaturing solvent of phosphate buffer, pH 7.0. In conclusion, natural human IFN-gamma forms oligomers, particularly dimers, in non-denaturing solution, and this oligomer formation is a reversible reaction.