Protein kinases are enzymes that modify the function of other proteins by attaching phosphate groups to them. Since they are often involved in the regulation of the cell cycle, cell migration and cell signaling, they are popular drug targets.

Kinases function intracellularly and thus in a reducing environment, their cysteine residues have to be maintained in the reduced state. Therefore, it is recommended to supplement the assay buffer with Reducing Agents (we advise 1-5 mM GSH or DTT). The affinity towards ATP and analogues is typically in the µM range, and binding to nucleotides often requires Mg2+ ions.