Using the PKA coupled assay with Kemptide as substrate, we compared the activity of the unbound Halo-PKA fusion with that of non-Halo fused PKA catalytic subunit (Fig. ). Activity of the fusion protein was significantly lower than that of the fusion protein), indicating that the fusion negatively impacted enzyme kinetics. This was not an unexpected result given numerous literature examples of impacts of fusions on enzyme activity . We also investigated the immobilization of our protein fusion onto magnetic HaloTag binding beads, and found that our construct was efficiently bound, up to a maximum concentration of 1.34 mg Halo-PKA/mL of a 20% resin suspension; a loading titration study performed with non-magnetic HaloLink Resin produced a similar result (data not shown; loading capacity = 1.13 mg Halo-PKA/mL of a 20% resin suspension). Having confirmed that the protein fusion was active in its free form and could be immobilized, we then proceeded to investigate its activity in its immobilized form.