Phosphagen (guanidino) kinases are enzymes that transphosphorylate a high energy phosphoguanidino compound, such as phosphocreatine (PCr) or phosphoarginine, which is used as an energy-storage and -transport metabolite, to ADP, thereby creating ATP. This subfamily is specific to bacteria and lacks an N-terminal domain, which otherwise forms part of the substrate binding site. Most of the catalytic residues are found in the larger C-terminal domain, however, which appears conserved in these bacterial proteins. Their functions have not been characterized.
Jiyao W et al.(2023). "The conserved domain database in 2023.",