Catalyzes the ATP- as well as probably the pyrophosphate-dependent phosphorylation of 'Ser-46' in HPr, a phosphocarrier protein of the phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS). HprK/P also catalyzes the pyrophosphate-producing, inorganic phosphate-dependent dephosphorylation (phosphorolysis) of seryl-phosphorylated HPr (P-Ser-HPr). The two antagonistic activities of HprK/P are regulated by several intracellular metabolites, which change their concentration in response to the absence or presence of rapidly metabolisable carbon sources (glucose, fructose, etc.) in the growth medium. Therefore, by controlling the phosphorylation state of HPr, the HPrK/P is a sensor enzyme that plays a major role in the regulation of carbon metabolism and sugar transport: it probably mediates carbon catabolite repression (CCR), and regulates PTS-catalyzed carbohydrate uptake and inducer exclusion. [HPr protein]-L-serine + ATP = [HPr protein]-O-phospho-L-serine + ADP + H(+) [HPr protein]-O-phospho-L-serine + H(+) + phosphate = [HPr protein]-L-serine + diphosphate Kinase activity is inhibited by inorganic phosphate (Pi). In contrast to many other bacteria, neither kinase activity nor phosphorylase activity is affected by fructose 1,6-bisphosphate (FBP). Optimum pH is 7.0 for both kinase and phosphorylase reactions. Activity decreases to less than 10% of the maximal activity at pH 5.5. Homohexamer. Constitutively expressed. Transcription of S.bovis hprK is not significantly altered by growth rate or energy source. The Walker A ATP-binding motif also binds Pi and PPi. Both phosphorylation and phosphorolysis are carried out by the same active site and suggest a common mechanism for both reactions. Belongs to the HPrK/P family. PubMed:12610726 presented the dephosphorylation reaction catalyzed by HPrK/P as a phosphatase activity, but it is most likely a phosphorylase activity as shown in B.subtilis.