Enzyme II of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system: protein-protein and protein-phospholipid interactions

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Abstract
The mannitol-specific enzyme II (EII), purified free of phospholipid, exhibits a concentration dependence in its specific activity with P-HPr and mannitol as the donor and acceptor substrates, respectively. This concentration dependence, previously observed only in the case of the mannitol .dblarw. mannitol phosphate exchange reaction, indicates that an oligomeric form of the enzyme is responsible for catalyzing the phosphorylation reaction (P-HPr + mannitol .fwdarw. mannitol-P + HPr) as well as the exchange reaction. Kinetic analysis revealed that the monomeric enzyme has a much lower specific activity than the associated species. The specific activity can be increased by raising the steady-state level of phosphorylation of EII and also by adding phospholipid, demonstrating that phosphorylation and the binding of phospholipid facilitate the association process. Kinetic measurements and fluorescence energy transfer measurements demonstrate a strong preference of EII for phospholipids with specific head group and fatty acid composition.