*3.7. Effect of Metal Ions on Mal-mPEG5000-SPA and SPA*

Incubation of the enzyme was carried out by 10 mM of metal ions salts (chlorides including Ca2+, Mg2+, Cu2+, Zn2+, Mn2+, K+, NH4+, Hg+, Al3+, Fe3+, Ba2+ and Cd+), AgNO3 and EDTA at 40 ◦C for 30 min, and the residual activities were determined respectively. An enzyme that did not contain metal ions was chosen as control (100%).
