The redox state and the phosphorylation state of the mannitol-specific carrier of the E. coli phosphoenolpyruvate-dependent phosphotransferase system.

This review summarizes the recent developments in identifying the activity-linked cysteine as one of the phosphorylation sites on the mannitol-specific EII of the E. coli phosphoenolpyruvate-dependent mannitol transport system. Two phosphorylation sites have been identified, one being the HPr/P-HPr exchange site, the other being the mannitol/mannitol-P exchange site. The activity-linked cysteine and the second phosphorylation site are located in the same 14 residue peptide. Phosphorylation of the second site and phosphoryl group transfer to mannitol do not occur as long as the activity-linked cysteine is oxidized or alkylated. A kinetic scheme has been developed which accounts for the relationships between the redox state, the phosphorylation state and the activity of the carrier. Kinetics of the individual reactions determine whether the enzyme cycles through an oxidized/reduced state during a cycle of phosphorylation/dephosphorylation.