Organic Chemistry MCAT Practice Exam 2025 – The All-in-One Guide to Master Your Test Preparation!

In metal ion affinity chromatography, Ni2+ ions play a crucial role by specifically binding to proteins that have been engineered to possess a histidine tag. This technique exploits the strong interaction between the divalent nickel ions and the imidazole side chains of histidine residues in the proteins.

When proteins containing these histidine sequences are introduced into the chromatographic column that has been pre-treated with Ni2+, they bind effectively due to this interaction. The presence of the Ni2+ ions allows for the selective purification of histidine-tagged proteins from a mixture, as these proteins will adhere to the column while non-tagged proteins are washed away.

Later, to elute the bound histidine-tagged proteins from the column, a solution containing a high concentration of imidazole can be used, which competes with the histidine for the binding sites on the Ni2+. This strategy makes use of the specific affinity of the Ni2+ for histidine, thereby achieving a targeted purification process that is highly efficient and specific for histidine-tagged proteins.