The effect of inorganic phosphate on the activity of bacterial ribokinase

Ribokinase and adenosine kinase are both members of the PfkB family of carbohydrate kinases. The activity of mammalian adenosine kinase was previously shown to be affected by pentavalent ions (PVI). We now present evidence that the catalytic activity of E. coli ribokinase is also affected by PVI, increasing both the velocity and affinity of the enzyme for d-ribose. The K_m for ribose decreased from 0.61 mM to 0.21, 0.25, and 0.33 mM in the presence of 20 mM phosphate, arsenate, and vanadate, respectively. The activity of ribokinase was stimulated in a hyperbolic fashion, with the maximum velocity increasing 23-fold, 13-fold, and 11-fold under the same conditions, respectively. Activity was also affected upon the addition of phosphoenolpyruvate, suggesting that phosphorylated metabolites could be involved in enzymatic control. The similar effect of PVI on distantly related enzymes suggests that a common mechanism for activity is shared among PfkB family members.