HprK/P, the bifunctional histidine-containing protein kinase/phosphatase, controls the phosphorylation state of the phosphocarrier protein HPr and regulates the utilization of carbon sources by gram-positive bacteria. It catalyzes both the ATP-dependent phosphorylation of Ser-46 of HPr and its dephosphorylation by phosphorolysis. The latter reaction uses inorganic phosphate as substrate and produces pyrophosphate. Phosphoenolpyruvate carboxykinase (PEPCK) and the C-terminal catalytic domain of HprK/P are structurally similar with conserved active site residues suggesting these two phosphotransferases have related functions. The HprK/P N-terminal domain is structurally similar to the N-terminal domains of the MurE and MurF amino acid ligases.