2.6. Separation and purification of protease
The culture was harvested after 2 days’ growth at room temperature. The crude enzyme preparation was subjected to ammonium sulphate precipitation, and the harvested culture was filtered through Whatman no. 1 filter paper of pore size 125 mm and centrifuged (REMIC-24BL) at 5000 rpm for 30 min at 4 ◦C. Ammonium sulphate was added slowly to the cell-free culture filtrate at 75% saturation to precipitate the protein, with continuous shaking and a magnetic stirrer. The precipitated protein was separated by centrifugation at 5000 rpm for 30 min and was dissolved in 0.5 mmol/L phosphate buffer, pH 7, dialysed and stored. This source of crude enzyme was used for further enzyme characterization. At each step, the protease activity and total protein content were measured in an ultraviolet spectrophotometer.