In pET sytem manual, it is stated that after protein expression and during harvesting cells of BL21 (DE3), you should wash the pellet with 20mM Tris-HCl pH 8. Does anyone know the reason for this?
This is a helpful step to get high protein purity because not only your protein is inside the solution, but there are many kinds of protein and not useful compounds, so you want to reduce unwanted material inside your solution.