The obtained supernatant (≈500 μl) was transferred to each new 1.5 ml Eppendorf tube with 350 μl of isopropanol, mixed by pipetting and centrifuged at 15,000 g for 10 min. The pellet was rinsed with 1 ml of ice-cold 70% ethanol, centrifuged at 15,00 0 g for 5 min and dried at room temperature. Dried pellet was resolved in 100 μl of 20mM Tris–HCl, pH 8.0.