2.7. Ammonium Sulfate Precipitation

Ammonium sulfate was added at more than one saturation ratio (20-80%), and to reach the best ratio of ammonium sulfate, salt was added progressively to each 10 ml enzyme solution in the ice bath and magneticstirrer for 1 h. The final solution was centrifuged at 10,000 rpm/min for 10 min. The precipitate was kept and the supernatant was discarded, 25ml phosphate buffer saline pH 7.2 was dissolved in the precipitate, and the activity of enzyme and protein concentration were calculated ( 12 ).