DISSOCIATION EQUILIBRIUM OF HUMAN RECOMBINANT INTERFERON-GAMMA

The biologically active form of interferon gamma is a dimer composed o f two noncovalently bound identical polypeptide chains of 17 kDa each. In this study, it was found that dissociation of the dimer into monom ers significantly reduced the fluorescence quantum yield and the effic iency of the intermolecular Tyr to Trp radiationless energy transfer. The same process caused significant changes in the fluorescence decay and in the fluorescence anisotropy decay. The kinetic and thermodynami c parameters of the dimer-monomer equilibrium were determined by fluor escence measurements at different temperatures and by a theoretical ma thematical model. Dissociation of the dimers into monomers was an endo thermic process and was favored by concentrations of the protein lower than 1 mu M and by increasing the temperature. It was accompanied by formation of aggregates, a slow and partially reversible process leadi ng to inactivation of the interferon. It is suggested that certain mon omeric conformers are competent for aggregation.