Detection and molecular weight determination of polyethylene glycol-modified hirudin by staining after sodium dodecyl sulfate-polyacrylamide gel electrophoresis

This article describes a general method for detecting pegylated proteins directly after SDS-PAGE. The proteins to which polyethylene glycol (PEG) molecules are attached are stained with a barium iodide solution. The staining is based on the formation of a barium iodide complex with PEG. The described method combines a specific staining of PEG molecules with the high resolution of the SDS-PAGE method. It is shown that pegylated protein is detectable on SDS-PAGE as well as on IEF at concentrations that are not detectable by Coomassie protein staining. This paper also describes the determination of the molecular weight of pegylated hirudin by calibrating SDS-PAGE with polyethylene glycol of different molecular weight. Under the conditions used, PEG showed linear mobility during electrophoresis. However, the use of nonpegylated proteins as standards resulted in incorrect molecular weight values due to the lower mobility of the pegylated protein during electrophoresis. The method described might reflect a general method for determining molecular weight of pegylated proteins.