Consider an experiment where your goal is to isolate Bruton’s tyrosine kinase (BTK) enzyme from a whole‑cell lysate. You have an affinity chromatography column with a tyrosine kinase inhibitor molecule covalently attached to the beads. The tyrosine kinase inhibitor binds and inhibits BTK. As a result of the experiment, you are able to elute BTK from the column, but in a mixture of other tyrosine kinases. Why are tyrosine kinases other than BTK present in the eluate?

Kinase inhibitor has low specificity

Explanation:

In humans, Bruton's tyrosine kinase (BTK) is a protein tyrosine kinase encoded by the BTK gene, which plays key functions in the mechanisms of development, differentiation, and signaling of B-lymphocytes. In the last years, many BTK inhibitor drugs have been developed, including Ibrutinib, Acalabrutinib and  Zanubrutinib. It has been shown that kinase inhibitors may have low specificity because these molecules exhibit a high conservation level in the ATP binding pocket, which is known as 'inhibitor promiscuity'.