To create an immobilized PKA fusion protein, we selected the HaloTag protein, a modified haloalkane dehalogenase that catalyzes the formation of covalent links to a solid support material functionalized with HaloTag-specific chloroalkane ligands . Prior research demonstrates that HaloTag has proven to be a compatible fusion partner with multiple enzyme classes, resulting in immobilized enzymes possessing the desired characteristics of robust activity and reusability .