Increased stability of PEG-PPG conjugated human urokinase against autolysis

Human urokinase (UK) was easily degraded during the incubation at 37 degrees C in a time-dependent manner. The degradation was also observed in the presence of trypsin inhibitors, suggesting that UK was not degraded by exogeneous trypsin-like serine protease but by autolysis. In this cases, the A-chain of UK was selectively degraded. Polyethylene glycol-polypropylene glycol conjugated urokinase (PEG-PPG-UK) was not degraded after prolonged incubation at 37 degrees C. These results demonstrated that PEG-PPG modification completely blocked the degradation of UK by autolysis.