Imidazole

''The high affinity of Ni2+ to histidine is suited very well for the purification of recombinant proteins, which are fused to a His-tag (usually 6 histidine residues at the N- or C-terminus of the protein). This modified protein can be expressed in Tetrahymena and other organisms as well and purified by nickel resin/columns. The bound protein can be eluted by imidazole, which competes with the histidine residues of the His-tagged protein for the nickel ions. The optimal concentration of imidazole differs depending on the protein, but ranges very often from 40 to 300 mM. We commonly use 250 mM imidazole.''

''Solutions of imidazole are stable for several years (at least 6 years). Buffers containing imidazole will turn to yellow. These solutions are still suitable to elute His-tag proteins.''

It is not necessary to autoclave the solution and to store it protected from light.

Materials

 * Imidazole
 * ddH2O

Method (makes 100 mL of 5 M solution)

 * 1) Dissolve 34.04 g of imidazole crystals in 90 mL of ddH2O and stir/shake continuously.
 * 2) Adjust volume to 100 mL.
 * 3) Sterilize by filtration using a 0.22 µ filter disc.
 * 4) Store at room temperature.