CHANGES IN THE CELLULAR-ENERGY STATE AFFECT THE ACTIVITY OF THE BACTERIAL PHOSPHOTRANSFERASE SYSTEM

The effect of different cellular free-energy states on the uptake of m ethyl a-D-glucopyranoside, an analogue of glucose, by the Escherichia coli phosphoenolpyruvate :carbohydrate phosphotransferase system was i nvestigated. The intracellular [ATP]/[ADP] ratio was varied by changin g the expression of the atp operon, which codes for the H+-ATPase, or by adding an uncoupler of oxidative phosphorylation or an inhibitor of respiration. Corresponding initial phosphotransferase uptake rates we re determined using an improved uptake assay that works with growing c ells in steady state. The results show that the initial uptake rate wa s decreased under conditions of lowered intracellular [ATP]/[ADP] rati os, irrespective of which method was used to change the cellular energ y state. When either the expression of the alp operon was changed or 2 ,4-dinitrophenol was added to wild-type cells, the relationship betwee n initial phospho-transferase uptake rate and the logarithm of the [AT P]/[ADP] ratio was approximately linear. These results suggest that th e cellular free-energy state, as reflected in the intracellular [ATP]/ [ADP] ratio, plays an important role in regulating the activity of the phosphotransferase system.