Sites of phosphorylation in recombinant human interferon-gamma

Recombinant human interferon-gamma was phosphorylated with ATP and c-AMP-dependent protein kinase. After phosphorylation, interferon-gamma was separated from the adenosine phosphates and the kinase and analyzed by SDS-PAGE, reverse phase HPLC, and HPLC peptide mapping. Comparison of the S. aureus V8 protease maps of intact and phosphorylated interferon-gamma showed that the maps were identical except that one peptide fragment elutes earlier in the map of the phosphorylated sample. This peptide was identified as the C-terminal fragment containing two serinyl phosphorylation sites at positions 132 and 142. This phosphorylated interferon-gamma exhibited a slightly higher specific antiviral activity than the intact protein.