Physical Mechanism for Regulation of Phosphoenolpyruvate-Dependent Glucose Transport Activity in Escherichia coli

The activity of the phosphoenolpyruvate-dependent glucose phosphotransferase system (PTS) in Escherichia coli is coupled to the oxidation-reduction potential. It is inhibited when the redox potential is increased above -300 mV either via substrate oxidation or via direct addition of oxidizing agents. Depending on the point of addition, dithiothreitol either blocks or reverses these effects. Inhibition occurs at the level of sugar binding to EII. A sulfhydryl group associated with EII activity undergoes reversible oxidation to, presumably, a disulfide, resulting in the conversion of EII from a reduced, high-affinity form to an oxidized, low-affinity form which has a 10^2-10^3 times lower affinity for the sugar. An identical change in affinity occurs as the result of the generation of a Δµ¯H+ during the oxidation of reduced N-methylphenazonium methosulfate or nicotinamide adenine dinucleotide. In this case, uncouplers and ionophores reverse the change. A mechanism is proposed in which the electrical potential difference across the membrane regulates the glucose PTS by shifting the midpoint potential of the EII-associated redox transition to more negative values. As a result, EII is converted to the oxidized, low-affinity state in the presence of a Δµ¯H+