Figure 3. Determination of relative enzyme activity of SS-mPEG-GPx1M. Temperature (A) and pH (B) profiles of GPx1M and SS-mPEG-GPx1M. (C) GPx1M and SS-mPEG-GPx1M were incubated in 50 mM PBS at 4°C for a period ranging from 1 to 150 days. (D) GPx1M and SS-mPEG-GPx1M were incubated in 50 mM PBS at −20°C for a period ranging from 1 to 90 days. (E) The resistance of SS-mPEG-GPx1M to protease hydrolysis. All values were converted to a relative value, and the highest enzyme activity was set as 100%. *p < 0.05, **p < 0.01, and ***p < 0.001 vs. GPx1M.