The two-phase chloramine-T method was applied in the radioiodine-labeling of polyethylene glycol modification of recombinant human interleukin-6 (PEG-rhIL-6). The iodine incorporation was determined by trichloroacetic acid (TCA) and a γ-ray survey meter. The labeled compound was purified by ultrafiltration. The purity of the labeled PEG-rhIL-6 was determined by TCA. The fragmentation of labeled protein was determined by SDS-PAGE-electrophoresis. The labeling efficiencies under different reaction conditions were compared

and the results demonstrated that the optimal conditions for total volume

pH

dosage of added protein

volume of chloramine-T

reaction time and temperature are 100μL

pH=7.4

25μg

15μL (20g/L)

40─50 min and room temperature

respectively.