Figure 1.

Conjugation of PEG to GCSF prevents precipitation at pH 7, 37°C. (A) GCSF (filled circles) and 20kPEG-GCSF (open circles) at 5 mg/mL and pH 6.9 were incubated at 37°C for time periods indicated, prior to measurement of protein solubility by absorbance of supernatant at 280 nm. (B) Effect of free PEG on GCSF precipitation. GCSF (black bar), 20kPEG-GCSF (gray bar), and GCSF + free 20kPEG (white bar) were incubated at 5 mg/mL, pH 6.9, and either 29°C or 37°C for 48 h. At the end of the incubation period, the samples were assessed for turbidity by measuring optical density at 600 nm. (C) Photographs of solutions of GCSF (left panel), free 20kPEG + GCSF (middle panel), and 20kPEG-GCSF after the 37°C incubation in B.