Which buffer is used to cause GFP to unbind from the column?

The correct buffer used to cause GFP to unbind from the column is an elution buffer. Elution buffers are specifically designed to disrupt interactions between the target protein, in this case, GFP, and the matrix of the chromatography column. This disruption allows the protein to be released or "eluted" from the column into the collected fractions.

Typically, elution buffers often contain higher concentrations of salt, different pH values, or specific ligands that induce changes in the binding interactions, enabling the target protein to detach effectively. In the context of GFP purification, the elution buffer chosen would have a composition that supports the stable release of GFP while ensuring that its structure and function are preserved.

The other buffers listed serve different functions in the purification process: equilibration buffers prepare the column for binding by establishing the proper ionic conditions, and binding buffers provide the appropriate conditions to promote the attachment of GFP to the column. Thus, they do not facilitate the unbinding process necessary for elution.