Dissociation of recombinant tumor necrosis factor-alpha studied by gel permeation chromatography

The structure of tumor necrosis factor-alpha (TNF-alpha) was studied using gel permeation chromatography. At an initial protein concentration of 0.4 mg/ml, the TNF-alpha exists as a compact trimer with a Stokes radius of 2.3 +/- 0.1 nm. This trimer dissociates as the protein concentration is decreased, and this dissociation is effected by pH. At the lower protein concentrations at pH 6.0 a species with a Stokes radius of 1.9 +/- 0.1 nm, possibly monomer, is evident. This species is not obvious at pH 7.0, but instead a species with a Stokes radius of 2.2 +/- 0.1 nm appears.